Effects of different fertilization sources on Olea europaea (Oleraceae). Impact on olives and oil yield and quality. Considerations on environmental sustainability and soil use. A review
Revisión sobre los efectos de diferentes fuentes de fertilizantes en Olea europaea (Oleraceae). Impacto sobre el rendimiento y calidad de aceitunas y aceite. Consideraciones sobre la sustentabilidad ambiental y uso del suelo
Busso, Mariano A 1*
; Liliana G. Suñer 1,2
; Roberto A. Rodríguez 1
1Departamento de Agronomía, Universidad Nacional del Sur, provincia de Buenos Aires, (8000)
Bahía Blanca, Argentina.
2Comisión de Investigaciones Científicas de la provincia de Buenos Aires (CIC), (1900) La Plata,
Argentina.
* Autor corresponsal: mariano.busso29@gmail.com
ABSTRACT
This review highlights the importance of olive trees growing in the southwest of Buenos Aires, Argentina. It also discusses the importance (1) of the different fertilizations forms in the determination of the various soil physicochemical and leaf chemical properties, olives yield, oil yield and quality, and (2) oil quality parameters. Cover crops can be beneficial to soil properties. The incorporation of organic manures is also beneficial to improve plant and soil physical and biological properties, which allows a better root development and longevity, and nutrient absorption. Additionally, organic crops can increase the oil yield and quality in comparison to non-organic treatments. Foliar fertilization can be a very efficient system for supplying N, P and K to olive trees. However, several applications are required to meet the needs of the crop. Olive yield decreases significantly when soil fertilization with N is eliminated for several consecutive years in comparison to the fertilization that is carried out annually. Nutrient overfertilization can lead to several negative effects from the environmental point of view. Fertilization with P might be unnecessary due to the extensive root system of the olive trees. Olive have a high K requirement since large amounts of K are removed each year at harvest. However, fertilization with different levels of K had negligible effects on oil quality. Oil quality parameters were first associated with N concentrations in leaves and fruits. The phenolic content of the oil decreased linearly in relation to the increase of N in the leaves, which indicates a competition between the synthesis of proteins and the phenolic compounds.
Keywords: Fertilization; oil; olive; polyphenols; yield.
RESUMEN
Esta revisión (1) destaca la importancia del crecimiento de olivos en el sudoeste de Buenos Aires, Argentina, y de diferentes (2) formas de fertilización en la determinación de varias propiedades fisicoquímicas del suelo y químicas de las plantas, del rendimiento de aceitunas, y del rendimiento y calidad del aceite, y (3) parámetros de calidad del aceite. Los cultivos de cobertura pueden beneficiar las propiedades del suelo. Los abonos orgánicos al suelo pueden mejorar las propiedades físicas y biológicas de las plantas y del suelo, y permiten un mejor desarrollo y longevidad de raíces, y de absorción de nutrientes. Los cultivos orgánicos pueden incrementar el rendimiento y calidad del aceite en comparación a los tratamientos no orgánicos. La fertilización foliar puede ser un sistema muy eficiente para abastecer N, P y K a los árboles de olivo. Sin embargo, se necesitan varias aplicaciones para satisfacer las necesidades de la cosecha. El rendimiento de los olivos disminuye significativamente cuando la fertilización con N del suelo es eliminada por varios años consecutivos en comparación a la fertilización producida anualmente. La excesiva fertilización con nutrientes puede producir varios efectos negativos desde el punto de vista ambiental. La fertilización del suelo con P podría no ser necesaria debido al sistema radical extensivo del árbol de olivo. Los frutos del olivo tienen un alto requerimiento de K por lo que grandes cantidades de K son removidas cada año con la cosecha; sin embargo, la fertilización con diferentes niveles de K tuvo efectos despreciables en la calidad del aceite. Los parámetros de calidad del aceite se asocian mayormente con las concentraciones de N en hojas y frutos. El contenido de fenoles en el aceite disminuyó linealmente en función del incremento de N en las hojas, indicando una competencia entre la síntesis de proteínas y compuestos fenólicos.
Palabras clave: Aceite; fertilización; olivos; polifenoles; rendimiento.
Original recibido el 3 de mayo 2022,
aceptado el 23 de agosto 2022.
Publicado en línea el 2 de septiembre 2022.
INTRODUCTION
1.1. The olive in Argentina and in the southwest of the Buenos Aires Province
Currently, Argentina is the major producer and exporter of olive oil in South America and the tenth to a worldwide level (COI, 2015). The southwestern region of the province of Buenos Aires is made up of the semi-arid, arid and sub-humid-dry pampas, with 6,500,000 ha, divided into 12 districts. Its agricultural productivity is lower than that of the rest of the Pampas, a consequence of the prevailing agroecological conditions (Cincunegui, et al., 2019). The Region has competitive advantages derived from its proximity to the largest port in the country (Ingeniero White port), an adequate transport system and the provision of related services necessary for the commercialization and general development of the activity (Cincunegui et al., 2019).
The National University of the South (UNS) is linked to the group of regional olive growers in order to generate, in an interdisciplinary way, information of a technological nature. This information should provide a firm basis for the development of a modern olive growing, that promotes and supports the production of quality oil in the arid and sub-humid zones of the province of Buenos Aires. Therefore, a group characterized by its high capacity for innovation, adequate treatment of the fruit, search for quality and collaborative action by different agents has been formed in the region (Rueda, 2016).
The oil produced in the area is distinguished by an oleic acid content with values greater than 70%, widely higher than the national average percentage. If its low levels of campesterol and free acidity are added to this data, the extra virgin oil from the south of Buenos Aires is chemically among the best at the national level, having received several national and international awards for its high quality (Cincunegui et al., 2019). This is due to characteristics such as the type of soil, the proximity to the sea, cold winters and a temperature range that favor the slow ripening of the fruit, high levels of phenols and a high proportion of oleic acid. These factors definitely influence the aromatic and chemical profile of the oils.
1.2. Fertilization systems and challenges for southwestern Buenos Aires Province
A large part of the producers of olive groves in the southwest of Buenos Aires use foliar fertilization with macronutrients (N, P and K) as the only method to increase the production of olive groves. This type of application is only recommended, how- ever, for fertilizing with micronutrients (e.g., B, Fe, Mn, etc.). In addition, if one takes into account that: (1) depending on the quantities in which these nutrients are necessary for the olive tree (if high, their absorption must be via roots), (2) the very low absorption efficiency via the leaves (caused by the presence of leaves with pubescent undersides), (3) the large amount of fertilizer that is not absorbed due to dripping, evaporation, drift, etc., several foliar applications should be made throughout the cycle. Annually, most of the regional producers do not make more than two or three foliar applications, assuming that the crop is well nourished. In this framework, more efficient fertilization methods should be found that not only incorporate inorganic nutrients to the olive grove but also provide organic matter to the soils where this species is grown. This is important to not only have current fertility (inorganic nutrients), but also potential fertility (i.e., organic matter that slowly releases inorganic nutrients).
A study is currently being conducted at the Agronomy Department UNS to determine which of different fertilization sources is the best to improve (1) different soil physicochemical or leaf chemical properties, (2) fruit quantity, and (3) oil quantity and quality. The different fertilization sources include a (1) nitrogen-fixing grass-legume consociated cover crop (Avena sativa L. – Vicia villosa L.) between the rows of olive trees, (2) commercial organic fertilizer, or (3) an inorganic fertilization of the leaves or the soil with macronutrients (N, P and K). In addition, a zonal harvest time will be determined that optimizes the quantity and quality of the obtained oil. The originality of such study consists in using organic fertilizers and nitrogen fixation through cover crops (e.g., Vicia faba) in order to obtain alternative ways to foliar or soil fertilization with macronutrients.
The incorporation of alternative intensive crops such as olive trees by the producer will contribute to carbon sequestration and reduction of soil losses due to erosion, common in agricultural production, increasing sustainability and reducing the degradation of the agroecosystem. Although the SOB is characterized by developing agricultural and livestock activities, olive growing has become highly relevant, even more in times of drought. This is due to the great resistance to drought of Olea europaea (Mechri et al., 2019).
A review on the effects of different fertilization systems on soil and plant properties, olives yield, and oil yield and quality follows:
FERTILIZATION SYSTEMS ON SOIL AND LEAF. PLANT RESPONSES IN TERMS OF OLIVE AND OIL YIELD AND QUALITY
2.1. Soil management systems in olive orchards: Traditional system versus cover crops between the rows of olive trees
Soil tillage is the traditional soil management in olive orchards. The effect of tillage on infiltration varies according to the location and type of soil, and the methods used for tillage (Gómez et al., 1999). In many cases, the greatest infiltration of water only occurs for a short period of time immediately after the passage of the machinery (Pastor et al., 2000). Tillage, however, could result in the degradation of the soil structure which can significantly reduce the rate of water infiltration causing runoff and erosion processes (Abid & Lal, 2009). Such undesirable effects are especially evident in olive trees present on steep slopes (Romero et al., 2007; Gómez et al., 2009a). Therefore, the environmental, hydrogeological, and socioeconomic consequences can be serious at both farm and basin scales (Xiloyannis et al., 2008). In addition, the combination of intensive tillage and high air temperature induce an oxidative metabolism in the soil, determining a high rate of mineralization of organic matter.
A significant loss of soil organic carbon leads to a further deterioration of the soil and its hydraulic properties, precisely those that allow a better recharge and storage of rainwater within the soil (Strudley et al., 2008).
An alternative opportunity to manage the soil in olive orchards is given by the use of cover crops that eliminate most of the disadvantages of conventional tillage. This practice reduces runoff and soil erosion by interception of raindrops, thus reducing their erosive impact on the soil and accelerating the infiltration of excess surface water. Furthermore, soil cover, ensured by the resulting litter (cover crop residues left on the soil surface), conserves soil moisture and reduces water evaporation from the soil surface. Some studies indicated an increase in soil moisture in olive orchards with cover crops as a result of an increase in the infiltration rate and in the content of organic carbon in the soil (Durán-Zuazo et al., 2009; Gómez et al., 2009a, 2009b). At present, there are contradictory results on the effects of soil management on the productive performance of olive trees. Gomez et al. (1999), in a 15-year trial, did not observe differences in yield between mature olive plants that grew according to the conventional soil management systems and no-till (weed control using the herbicide simazine). The differences were recorded in a very dry experimental year (67% of the average annual rainfall) in which the non-tillage of the soil produced almost twice as much as the conventional soil management system. The authors suggested that the presence of roots in the topsoil in the no-tillage system favored water uptake by trees rather than evaporation of water from the soil. Ferreira et al. (2013) compared three management systems for mature olive orchards during 2002-2011: glyphosate, soil tillage, and sheep walking. These authors reported the highest cumulative olive yields in the glyphosate treatment applied once a year in April.
Different results were reported by Gucci et al. (2012) who obtained a higher fruit and oil yields in young olive orchards managed with soil tillage compared to orchards that grew with a permanent natural cover. However, the same authors suggested that the negative effect on yield could be attributed to an early establishment of the permanent cover and recommended delaying its adoption to the third or fourth year after orchard planting depending on tree growth Soil and water conservation are essential for ecosystems to be sustainable in the long-term (Mirsky et al., 2013). Cover crops are increasingly recognized as a critical part of a sustainable agricultural production, based on the combination of productivity with the reduction of environmental risks (e.g., less use of herbicides due to less presence of weeds) (Schipanski, et al., 2014). The inclusion of cover crops (e.g., legumes) can increase the amount of particulate organic matter in the soil (Restovich et al., 2011). As a result, it is expected that it will also affect the dynamics of N in the soil (Beltrán et al., 2014).
The organic matter of soils is their most important nutrient reserve (Rani Sarker et al., 2018). The availability of these nutrients is a function, at least in part, of soil pH (Mengel & Kirkby, 2001). Soils with a pH between 5.5 and 7.5 are those that determine a greater availability of macro and micronutrients (Mengel & Kirkby, 2001). Therefore, the reduction of soil organic matter directly affects its quality and productivity (Beltrán et al., 2018). Thus, a permanent or semi-permanent organic cover of the soil is necessary to ensure the maintenance of its quality (Fuentes et al., 2009). Cover crops increase carbon levels in the soil and enhance its accumula- tion in the first layer of the soil due to deposition of crop tissues. This represents a greater stability for the soils since higher levels of carbon on the surface reduce erosion processes (Duval et al., 2016). The scarce or null contribution of residues could cause negative balances of the organic matter of the soil (Mazzilli et al., 2014), reducing the contribution of nutrients (Cruzate & Casas, 2012) and increasing their losses. This is due to the erosive processes that determine the lack of a soil coverage (Duval et al., 2017). Cover crops are not incorporated as green manures or harvested, and can fulfill many functions such as: (1) physical protection of the soil from solar radiation, wind and rain, (2) weed control (Alonso-Ayuso et al., 2018), (3) a greater contribution of organic carbon (Álvarez et al., 2005), (4) prevention of erosion, (5) increase in infiltration, (6) promotion of the capture of mobile nutrients (N and S), (7) reduction of their losses by leaching and (8) pest and disease control (Quiroga et al., 2009; Rimski Korsakov et al., 2015). It should also be considered that the presence of cover crops stimulates microbial activity in the soil and thus affects the availability of some nutrients (Kunze et al., 2011) and their distribution in the soil profile. The latter is the result of the absorption of water and nutrients from deeper layers in the soil, and their re-incorporation into the soil at the surface once the cover crop tissues dry out and decompose, producing a marked stratification and an increased soil nutrient density (mainly those that are not very mobile) at the soil surface. For example, in the case of phosphorus (P) and potassium (K), due to their low mobility, cover crops have an effect of stratifying their concentrations. As a result, there is an increase in them on the surface (Tiecher et al., 2012).
The cover crop fixes nitrogen during the autumn-winter season and releases it in spring-summer, after incorporating its biomass into the soil (Kramberger et al., 2009; Tosti et al., 2012). This situation allows the substitution of inorganic nitrog- enous fertilizers, which is very important from the environmental point of view, contributing to the sustainability of the production systems (Da Silva et al., 2007). Although a significant amount of N may exist in the aerial part of cover crops, the actual amount of N that will remain available will depend on the amount of waste that decomposes and the dynamics of mineralization/immobilization of each type and amount of waste contributed to the soil (Sá Pereira, 2013). The N maintained in the organic form is, compared to that provided by fertilizers, less prone to losses due to leaching, volatilization or denitrification, since it is made available slowly, accord- ing to the mineralization of plant residues (De Sá Pereira et al., 2014). Furthermore, N incorporated into the soil from plant biomass is more efficiently used by plants than N derived from fertilizers (Reicosky & Archer, 2005). The availability of N from cover crop residues will depend on their rate of decomposition, which is directly related to environmental conditions (e.g., water, light) and their C/N ratio.
If the C/N ratio is low, a high net mineralization will occur (Mengel & Kirkby, 2001). Soil fertility management requires an integrated strategy to maintain long- term nitrogen stocks while managing short-term nitrogen dynamics (Lawson et al., 2013). Species belonging to the Fabaceae family (e.g., vetch, Vicia spp.) are important sources of nitrogen used to meet these goals (Spargo et al., 2016). Vetch is an annual, winter species that is widely adapted to most areas and has a very satisfactory natural reseeding. In addition, it has a low C/N ratio (generally 10:1 to 15:1) that results in a rapid biomass decomposition, with most N mineralization occurring during the first 4 to 8 weeks of spring (Poffenbarger et al., 2015); it can produce more than 150 kg ha-1 of total N (Teasdale et al., 2012). Vetch has the ability to fix atmospheric N and recycle soil N, supplying it with very relevant amounts (Benincasa et al., 2008) and increasing crop productivity (Baigorria & Cazorla, 2009).
2.2. Soil commercial organic fertilizers
Organic production is a new agricultural production system that avoids the use of synthetic and chemical fertilizers applied to the soil. The environmental effects on human health encourage agricultural producers to replace the use of these chemical fertilizers with organic ones (Fayed, 2005). In addition, the incorporation of organic manures matter will help create favorable conditions for root development and nutrient absorption, since they provide elements that allow a better soil structure, managing to improve infiltration, drainage, aeration, moisture and nutrient retention (Bueno & Oviedo, 2014).
Relevant organic materials incorporated into olive orchards include chopped pruned material, raw organic manure, olive mill wastewater, compost and non-composted organic manures. Although the direct application of non-composted organic manures is common, it is not recommended because of the risk of spreading pathogens, parasites and weed seeds, all of which are eliminated during the composting process (Larney & Hao, 2007). Different composts have varying nutrient concentrations depending on the source materials used for their preparation (Cayuela et al., 2004). Concentrations of 1.4-2.5% total N, about 0.3-1% P and 2.1-2.9% K are common in the dry matter (Sánchez-García et al., 2016). In a study conducted by Cayuela et al. (2004), 40 kg compost tree-1 was applied in an irrigated orchard. The potential contribution of the compost to N, P and K tree nutrition in that study was 75-84, 11-17, and 100-120 kg ha-1, respectively. These amounts are about 50% of the recommended levels of 150 (N), 30 (P) and 250 (K) kg ha-1, respectively (Erel et al., 2018). In an orchard fertilized with compost there were increases in (1) organic matter content, (2) cation-exchange capacity, (3) soil hydraulic conductivity, (4) soil water retention (Cayuela et al., 2004), (5) the humic fraction of the soil, (6) aggregate stability (Whalen et al., 2003), (7) soil organic carbon content (Palese et al., 2014), and (8) mineral N content in compost was usually one order or magnitude lower than total N (Sánchez-García et al., 2016). Most of the N in the compost is in organic form, which makes it less liable to migrate downward through the soil because of heavy rains or irrigation (Dahan et al., 2014).
Organic matter is not only necessary for plant nutrition as slow-release fertilizer but also essential for efficient plant production systems (Steve, 2009). Composting is recommended for olive cultivation in arid and semi-arid regions, especially in sandy soils, which are limited by water resources (Abdel-Nasser & Harash, 2001).
The increase of soil organic matter is a slower and more complex process than its decomposition, making thus necessary the addition of organic manure if the main objective is a sustainable production (Diacono & Montemurro, 2010). The integrated nutrient management sustains an appropriate use of the combinations of organic and inorganic fertilizers, addressed to restore the soil organic matter, improve the availability and efficiency of soil nutrient use, and maintain or improve the soil biological, chemical and physical properties (Hernández et al., 2014).
The traditional organic fertilizers (residues of agricultural and feeding processes) have maintained the soil productivity for thousands of years. In the modern horticultural systems, friendly with the environment, organic fertilizers are often used to improve the soil physical and biological properties. Use of the organic matter in the fertilization of plants contribute to improve the soil chemical and biological properties. The organic matter increases the (1) organic carbon content, (2) soil biological properties (microflora and microfauna), (3) cation exchange capacity, and (4) soil structural stability (Giusquiani et al., 1995; Bravo et al., 2012), and reduce the (5) apparent density and (6) formation of crusts in the soil surface area (Chang et al., 2010). This improves the water retention, the water infiltration rate, and the soil hydraulic conductivity (Chang et al., 2010; Bravo et al., 2012) conducing to a greater harvest yield (Kwabiah et al., 2003; Chang et al., 2010; Jha et al., 2011; Marzouk & Kaseem, 2011). In addition, the organic manure can be beneficial to the harvest and soil on the long-term (Tirol-Padre et al., 2007). This is because the organic matter is mineralized during the growing season, gradually providing nutrients for plant uptake, more slowly than the mineral fertilizers. Baldi et al. (2010) observed that repeated applications of compost in a peach orchard increased root proliferation and longevity compared to soil without aggregates.
However, according to Aisueni et al. (2009), Amoah et al. (2012) and Bravo et al. (2012), the sole use of organic fertilizers as substitutes for chemical fertilizers is not enough to maintain the productivity of high-yielding crops. In turn, Lu et al. (2011) observed that the partial replacement of inorganic fertilizers with organic ones met the nutrient demands of crops and maintained the efficacy of macronutrients. This suggests that the combination of the organic and mineral fertilizers could be more efficient than the application of any of them separately.
Organic fertilizer application or compost amendment resulted in (1) lower pH values, (2) higher cation exchange capacity, (3) an increase of olive tree yields, (4) adequate mineral contents in leaves during the growing cycle of olive trees for obtaining an economical yield, (5) increases of the percentage of fruit establishment, (6) reductions in times of fruit fall, (7) increases in the soil N, P and K availabilities, (8) an increase of soil organic matter content, and (8) an increase in the soil water content and olive tree performance compared with the control (Roussos et al., 2017; Chehab et al., 2019).
Anastasopoulos et al. (2011) found that overall, olive oil from organic cultivation was of superior quality in comparison to the non-organic treatment. The utiliza- tion of compost improved significantly the oil yield by about 100% (Chehab et al., 2019). The organic olive virgin oil was of a superior quality in comparison to the conventional olive virgin oil: lower values of acidity and of peroxide index, greater stability and a greater value from the organoleptic point of view (Gutiérrez et al., 1999; AL-Kahtani & Ahmed, 2012).
The optimal pH values for olive cultivation are between 7 and 8.5 with respect to the availability of nutrients necessary for its correct growth and fruiting (Porta Casanellas & López Acevedo, 2005). Since the pH values found in the southwest of Buenos Aires are close to neutrality (Aguirre et al., 2011), they would not be restrictive for soil fertilization with macronutrients (N and K).
2.3. Inorganic foliar fertilizers
On numerous occasions, especially in dry years and very limestone soils, foliar fertilization can be a very efficient system for supplying nutrients to the olive tree. N and K are very well absorbed when applied by this method and P does so acceptably (Vega et al., 2018). However, such macronutrient fertilization is not recommended because these elements are needed in high quantities by the plant and the absorption by the leaves is not enough to supply the demand (Christensen, 2005). The amounts of macronutrients applied in this way is small, so several applications are required to meet the needs of the crop.
Foliar fertilization during plant growth has been a topic of recent research (Erel et al., 2013; Haytova, 2013). It is known that supplemental foliar nutrients can correct the mineral status of plants, improve fruit yields and quality, resistance to diseases, pests and drought tolerance (Haytova, 2013). However, the use of foliar fertilizers based on N, P and K led to a significant decrease in the content of phenolic com- pounds in the oil, although they seemed to significantly improve the level of most volatile compounds, especially hexanal (Dabbaghi et al., 2019).
In fact, several studies have focused on the effects of foliar fertilization on the antioxidant profile and fatty acid composition of the olive oil (Fernández-Escobar et al., 2006; Dag et al., 2009; Tekaya et al., 2013). Single and combined applications of the macronutrients N, P and K via foliar fertilization from 2.5 to 7.5 g/L have increased the weight, size and oil percentage of the fruits compared to unfertilized olive trees (Hussein & Abd Elall, 2018). Foliar fertilization with N applied at the end of the winter break, and B, Mg, S and Mn at the beginning of flowering, caused a significant decrease in phenols, tocopherols and carbohydrates in olive fruits. Thus, a high correlation was observed between the concentration of nutrients in the plant and the chemical composition of those fruits (Tekaya et al., 2014). Ben Mimoun et al. (2004) reported that foliar fertilization improves the quality of olive oil. The seasonal pattern of foliar macro and micronutrients of olive cultivation is affected by environmental, varietal and management effects that must be considered in the preparation of nutritional standards (Fernández-Escobar et al., 1999). Foliar nutrient analysis is the best method to diagnose the nutritional status of a tree and represents an important tool to determine future fertilization requirements.
2.4. Inorganic fertilizers applied to the soil
Morales-Sillero et al. (2007) studied the effect of fertilizing the water for irrigation on the oil quality and yield with different dosages of the fertilizer 4N-1P-3K. The oil yield increased as the fertilizer dosage also increased. This was due to an increased number of fruits. However, the oil quality was negatively affected on trees fertilized with 400 and 600 g of N per tree during the irrigation season in comparison to the control trees and those fertilized with 200 g of N.
Among the mineral elements of the soil that the olive tree requires the most are N, P and K (Bueno & Oviedo, 2014). These authors suggested which are the best mo- ments to apply nitrogenous and phosphorous fertilizers during the crop cycle. When the olive tree is young, the greatest needs are N and P (Bueno & Oviedo, 2014). However, when the olive grove is in full production and without any limitation to its growth, the highest mineral requirements are fundamentally of N and K.
The way to estimate the need for fertilization is by carrying out a soil analysis. This practice must be taken into account by the olive grower as the main tool for nutritional diagnosis before planting the olive grove. Over the years and as the olive grove grows and develops, the soil analysis must be complemented with the corresponding foliar analysis, for an efficient nutritional management. The amount of nutrients removed annually in the olive harvest is relatively low, suggesting that fertilizer applications could be more conservative than those usually recommended by soil and leaf tissue analysis laboratories. Thus, with a fruit yield of 2500 kg ha-1, the nitrogenous fertilizer to be applied should not exceed 20 kg N ha-1 year-1. This amount of N should be applied each year, to increase the efficiency in the use of N, given its characteristic of mobility in the soil and plant (Rodrigues et al., 2012). Olive yield decreases significantly and progressively when nitrogen fertilization is eliminated for 4 consecutive years, compared to fertilization carried out annually (Rodrigues et al., 2011). An increase in olive yield has been observed with applica- tions of N to the soil, while those of phosphorus and potassium were made by foliar application; nevertheless, prior to the applications, the foliar analysis indicated adequate levels of nutrition in the plants (Centeno & Campo, 2011). In general, it is observed worldwide that olive growers overfertilize the crop, particularly with N. Annual applications of 80 to 200 kg N ha-1, and even higher, are common in many areas of the Mediterranean zone (Fernández Escobar, 2011). The excessive use of N in agriculture translates into a decrease in its use efficiency and several negative ef- fects from the environmental point of view (Raun & Schepers, 2008). Some studies have proposed that phosphorus fertilization is unnecessary because the extensive root system of the olive tree absorbs adequate amounts of such element. Olive fruits have a high K requirement, since large amounts of K are removed each year at harvest. That is why K deficiency has very negative effects on production (Fernández-Escobar et al., 2008; Therios, 2009).
2.5. Fruit and olive oil quality parameters
Oil quality parameters were first associated with N concentration in leaves and fruits, which increased with nitrogen spraying. Potassium level had negligible effects. The phenolic content of the oil decreased linearly as a function of the increase of N in the leaves, indicating a competition between proteins and phenolic compounds in them. In general, the saturation level of fatty acids decreased with the N of the fruits, resulting in an increase in polyunsaturated fatty acids. Free fatty acids increased with increasing fruit N levels. The high load of fruits reduced their N content and consequently improved the quality of the oil (Erel et al., 2013). The high efficiency of foliar application reduces the need to apply fertilizers to the soil and thus decreases nutrient leaching/runoff as well as the impact of fertilizers on the environment (Dong et al., 2005; Rezk et al., 2008).
The process of development and ripening of the fruit is the result of a combination of biochemical and physiological changes that take place under strict genetic control, but with the influence of environmental factors, the age of the olive tree or the nutritional status of the tree (Connor & Fereres, 2005). The maturity of the fruits at the time of harvest influences the organoleptic quality and the properties of virgin olive oil. The highest quality oils are obtained if fruits with optimal ma- turity index are harvested (Jiménez Herrera et al., 2012). In addition, post-harvest and technological factors, such as transport, storage, washing, grinding, beating, etc., directly affect the organoleptic characteristics and chemical composition of the oils obtained (Jiménez & Carpio, 2008). The state of maturity of the olive is one of the most important factors associated with the sensory quality of virgin olive oil (Youssef et al., 2010). Apart from the well-known effects of olive ripening on fat yield, fruit deterioration, color, etc., the ripening factor must be a priority criterion to define the organoleptic quality of the oil. Depending on this state, the chemical composition (triglycerides and minority compounds) of the elaborated oil suffers alterations that, depending on the time of harvesting the fruit, exceed those produced by the variety factor (Sánchez Casas et al., 2006).
Numerous experimental evidence supports the existence of an inverse relation- ship between fruit ripening and content of polyphenols and volatile compounds (Bonoli et al., 2004; Rotondi et al., 2004; Gómez Rico et al., 2006; Youseff et al., 2010). During the ripening process, fruit weight, pulp-to-stone ratio, color, oil con- tent, chemical composition, and enzymatic activity change dramatically. All these parameters influence the firmness of the fruits, the ease of extracting the oil and sensory characteristics (Bouaziz et al., 2004; Menz & Vriesekoop, 2010). Generally, as the fruit ripens, the oil becomes less stable due to the increase in polyunsaturated fatty acids and the decrease in polyphenol content (Ayton et al., 2007; Morello et al., 2004; Rotondi et al., 2004). These changes are of high commercial importance because they determine the sensory characteristics of the oil, as well as its storage time. Fruits harvested early produce oil with a high content of polyphenols that con- tribute to the level of bitterness and spiciness. The oil is relatively more stable due to the antioxidant effect of polyphenols (Dýraman & Dibekliog¢ lu, 2009). However, harvesting too early will yield oils that are organoleptically unacceptable due to an excessive concentration of polyphenols.
The oil yield is extremely important for the producer and must be considered together with the quality indices to define the harvest time. It is documented that the percentage of oil increases significantly from the beginning of fruit maturity (Lavee & Wodner, 2004). The oil content increased as the maturity index increased, reaching a maximum at a medium level of maturity and then decreasing (Baccouri et al., 2007). Free acidity increased as maturation progressed and an increase in enzymatic activity was found, especially by lipolytic enzymes (Baccouri et al., 2007). In addition, the low free acidity was due to healthy fruits and their rapid processing and it was evidenced that, with advanced stages of maturity, the peroxide values turned out to be lower in the oils obtained (Matos et al., 2007). In general, as the fruits mature, the oil becomes less stable due to the decrease in polyphenol content, increasing the polyunsaturated fatty acids (mainly linoleic acid) and decreasing the chlorophyll contents (Ayton et al., 2007). The latter contributes to the stability of the oil when it is found in fruits not yet harvested (Vincenzo et al., 2006); it is seen as a positive aesthetic characteristic of olive oil, giving it the green color, although the pro-oxidant effect is a negative attribute (Ayton et al., 2007).
Vitamin E is another important antioxidant that is formed by the tocopherols á, â and ã in virgin olive oils. Usually, the activity of vitamin E of the virgin olive oils is greater than that described for other edible oils. Pigments are responsible for the oil color which is considered as a quality parameter. In the olive virgin oil, carotenoids and chlorophyll pigments can be found. Carotenoids have antioxidant activity which protect oils from autooxidation, while chlorophylls act as a pro-oxidant in light (Fernández-Escobar et al., 2006). These authors reported that fertilization and pruning do not appear to affect olive oil quality parameters such as the acidity, the peroxide values and the absorption of UV-vis.
FINAL CONSIDERATIONS
The importance (1) of different fertilizations forms in the determination of different soil physicochemical and leaf chemical properties, olives yield, oil yield and quality, and (2) of different oil quality parameters were discussed in this review. Cover crops can be beneficial to soil properties. The plant and soil physical and biological properties, and the creation of favorable conditions for root development, longevity, and nutrient absorption can be improved by the incorporation of organic manures. In comparison to the non-organic treatments, oil yield and quality can be increased by organic cultivation. N, P and K can be very efficiently applied via foliar fertilization to olive trees, although several applications are required to meet the needs of the crop. When soil N fertilization is not made by different consecutive years, olive yield decreases significantly in comparison to annual N fertilization. Because of the extensive root system of the olive tree, some studies have proposed that soil P fertilization is unnecessary. Olive fruits have a high K requirement since large amounts of K are removed each year at harvest. However, fertilization with different levels of K had negligible effects on oil quality. In contrast, N concentrations in leaves and fruits were first associated with oil quality parameters. As a function of the increase of N in the leaves, there was a linear decrease in the phenolic content of the oil, indicating a competition between proteins and phenolic compounds in the leaves.
BIBLIOGRAFÍA
Abdel-Nasser, G. & Harash, M. M. (2001). Studies on some plant growing media for olive cultivation in sandy soils under Siwa oasis conditions. Journal of Advance in Agricultural Research 6: 487-510.
Abid, M. & Lal, R. (2009). Tillage and drainage impact on soil quality: II. Tensile strength of aggregates, moisture retention and water infiltration. Soil and Tillage Research 103: 364-372. doi:10.1016/j.still.2008.11.004
Aguirre, M., Elisei, V., Commegna, M. & Santamaría, R. (2011). Evolución de la salinidad en un suelo irrigado del sudoeste bonaerense. Ciencia del suelo 29: 265-276.
Aisueni, N. O., Ikuenobe, C. E. Okolo, E. C. & Ekhator, F. (2009). Response of data palm (Phoenix dactylifera) seedlings to organic manure, N and K fertilizers in polybag nursery. African Journal of Agricultural Research 4: 162-165.
AL-Kahtani, S. H. & Ahmed, M. A. (2012). Effect of Different Mixtures of Organic Fertilizers on Vegetative Growth, Flowering, Fruiting and Leaf Mineral Content of Picual Olive Trees. American-Eurasian Journal of Agricultural and Environmental Science 12: 1105-1112. doi: 10.5829/idosi.aejaes.2012.12.08.1873
Alonso-Ayuso, M., Gabriel, J. L., García-González, I., Del Monte, J. P. & Quemada, M. (2018). Weed density and diversity in a long-term cover crop experiment background. Crop Protection 112: 103-111.
Álvarez, C., Barraco, M., Díaz Zorita, M., Scianca., C. & Pecorari, C. (2005). Uso de cultivos de cobertura en rotaciones con base soja: efecto sobre algunas propiedades edáficas y rendimiento de los cultivos en un Hapludol típico del noroeste bonaerense. Boletín de divulgación técnica Nº 87.
Amoah, A. A., Senge, M., Miyagawa, S. & Itou, K. (2012). Effects of soil fertility management on growth, yield, and water-use efficiency of maize (Zea mays L.) and selected soil properties. Communications in Soil Science and Plant Analysis 43: 924-935. doi:10.1080/00103624.2012.653028
Anastasopoulos, E., Kalogeropoulos, N., Kaliora, A. C., Kountouri, A. & Andrikopoulos, N. K. (2011). The influence of ripening and crop year on quality indices, polyphenols, terpenic acids, squalene, fatty acid profile, and sterols in virgin olive oil (Koroneiki cv.) produced by organic versus non-organic cultivation method. International Journal of Food Science and Technology 46: 170-178. doi: 10.1111/j.1365-2621.2010.02485.x
Ayton, J., Mailer, R., Haigh, A., Tronson, D. & Conlan, D. (2007). Quality and oxidative stability of Australian olive oil according to harvest date and irrigation. Journal of Food Lipids 14: 138-156. doi: 10.1111/j.1745-4522.2007.00076.x
Baccouri, B., Ben Temime, S., Taamalli, W., Daoud, D., Msallem, M. & Zarrouk, M. (2007). Analytical characteristics of virgin olive oils from two new varieties obtained by controlled crossing on Meski variety. Journal of Food Lipids 14: 19-34. https://doi.org/10.1111/j.1745-4522.2006.00067.x
Sistemas Productivos Sustentables. Fósforo, Nitrógeno y Cultivos de Cobertura. Bahía Blanca, Argentina (https://slideplayer.es/slide/1606310/, CD).
Baldi, E., Toselli, M. & Marangoni, B. (2010). Nutrient partitioning in potted peach (Prunus persica L.) trees supplied with mineral and organic fertilizers. Journal of Plant Nutrition 33: 2050-2061. https://doi.org/10.1080/01904167.2010.519080
Beltrán, M., Galantini, J., Brevedan, R. & Otero Estrada, E. (2014). Efecto del centeno sobre los niveles de carbono y nitrógeno del suelo. En: XXIV Congreso Argentino de la Ciencia del Suelo, Bahía Blanca, Buenos Aires. 5 al 9 de mayo.
Beltrán, M., Sainz Rozas, H., Galantini, J., Romaniuk, R. & Barbieri, P. (2018). Cover crops in the Southeastern region of Buenos Aires, Argentina: effects on organic matter physical fractions and nutrient availability. Environmental Earth Sciences 77: 428. https://doi.org/10.1007/s12665-018-7606-0
Benincasa, P., Tosti, G., Boldrini, A., Tei, F. & Guiducci, M. (2008). Poliennal results on soil N management and maize N nutrition by green manuring. In: Proc. of the 2nd Scientific Conference of ISOFAR, Modena, Italy, 16-20 June 2008, ISBN 978- 3-03736-023-1, pp. 194-198.
Ben Mimoun, M., Loumi, O., Ghrab, M., Latiri, K. & Hellali, R. (2004). Foliar potassium application on olive tree. In: Regional workshop on potassium and fertigation development in west Asia and North Africa (pp. 24-28). Rabat, Mo- rocco. 24-28 november.
Bonoli, M., Bendini, A., Cerretani, L., Lercker, G. & Gallina, T. (2004). Qualitative and semiquantitative analysis of phenolic compounds in extra virgin olive oils as a function of the ripening degree of olive fruits by different analytical techniques. Journal of Agriculture and Food Chemistry 52: 7026-7032. doi: 10.1021/jf048868m
Bouaziz, M., Chamkha, M. & Sayadi, S. (2004). Comparative study on phenolic content and antioxidant activity during maturation of the olive cultivar Chemlali from Tunisia. Journal of Agriculture and Food Chemistry 52: 5476-5481. doi: 10.1021/jf0497004
Bravo, K., Toselli, M., Baldi, E., Marcolini, G., Sorrentini, G., Quartieri, M. & Marangoni, R. (2012). Effect of organic fertilization on carbon assimilation and partitioning in bearing nectarine trees. Scientia Horticulturae 137: 100-106. doi: 10.1016/j.scienta.2012.01.030
Bueno, L. A. & Oviedo, A. S. (2014). Plantación del olivo. Estación Experimental Agropecuaria San Juan Centro Regional Mendoza – San Juan INTA. ISBN 978-987-521-496-5. Recuperated from https://inta.gob.ar/sites/default/files/script-tmp-inta_manual_plantacion_olivo.pdf
Cayuela, M. L., Bernal, M. P. & Roig, A. (2004). Composting olive mil waste and sheep manure for orchard use. Compost Science and Utilization 12: 130-136. https://doi.org./10.1080/1065657X.2004.10702171
Centeno, A. & Campo, M. (2011). Response of mature olive trees with adequate leaf nutrient status to additional nitrogen, phosphorus and potassium fertilization. Acta Horticulturae 888: 277-280. doi: 10.17660/ActaHortic.2011.888.31
Chang, K. H., Wu, R. Y., Chuang, K. C., Hsieh, T. F. & Chung, R. S. (2010). Effects of chemical and organic fertilizers on the growth, flower quality and nutrient uptake of Anthuriurn andreanum, cultivated for cut flower production. Scientia Horticulturae 125: 434-441. Recuperated from https://agris.fao.org/agris-search/search.do?recordID=US201301853527
Chehab, H., Tekaya, M., Ouhibi, M., Gouiaa, M., Zakhama, H., Mahjoub, Z., Laamari, S., Sfina, H., Chihaoui, B., Boujnah, D. & Mechri, B. (2019). Effects of compost, olive mill wastewater and legume cover crops on soil characteristics, tree performance and oil quality of olive trees cv. Chemlali grown under organic farming system. Scientia Horticulturae 253: 163-171. https://doi.org/10.1016/ jscientia.2019.04.039
Christensen, L. P. (2005). Foliar fertilization in vine mineral nutrition management programs. In: L.P. Christensen, D.R. Smart (Eds.). Proc. of the Soil Environment and Vine Mineral Nutrition Symposium (pp. 83-90). Davis: American Society for Enology and Viticulture.
Cincunegui, C., Lupín, B., Tedesco, L., Pérez, S., Fernández, L., Roldán, C. & Lobbosco, D. (2019). Consumo y territorio. Aceite de oliva producido en el Sudoeste Bonaerense. In: II Pre Congreso Argentino de Desarrollo Territorial y I Jornadas Patagónicas de Intercambio Disciplinar sobre Desarrollo y Territorio (pp.1-6). Bariloche. 29-30 abril. http://rodna.bn.gov.ar/jspui/handle/bnmm/322169
COI. (2015). International Olive Oil Council. Recuperado online: http://www.internationaloliveoil.org/S
Connor, D. & Fereres, E. (2005). The physiology of adaptation and yield expression in olive. Horticultural Reviews American Society of Horticultural Science 31: 155-229. Recuperated from https://digital.csic.es/bitstream/10261/11737/1/Connor_2005_The%20physiology%20of%20adaptation.pdf
Cruzate, G. & Casas, R. (2012). Extracción y balance de nutrientes en los suelos agrícolas de la Argentina. Informaciones Agronómicas de Hispanoamérica 6: 1-14. Recuperado de https://aulavirtual.agro.unlp.edu.ar/pluginfile.php/76796/mod_resource/content/2/Nutrientes/20/20Cruzate/20/20Casas/20/281/29.pdf
Dabbaghi, O., Tekaya, M., Flamini, G., Zouari, I., El Gharbi, S., M’barki, N., Laabidi, F., Cheheb, H., Attia, F., Aïachi Mezghani, M., Hammami, M. & Mechri, B. (2019). Modification of Phenolic Compounds and Volatile Profiles of Chemlali Variety Olive Oil in Response to Foliar Biofertilization. Journal of the American Oil Chemists’ Society 96: 585-593. doi: 10.1002/aocs.12201
Dag, A., Ben-David, E., Kerem, Z., Ben-Gal, A., Erel, R., Basheer, L. & Yermiyahu, U. (2009). Olive oil composition as a function of nitrogen, phosphorus and potassium plant nutrition. Journal of the Science of Food and Agriculture, 89:1871- 1878. https://doi.org/10.1002/jsfa.3664
Dahan, O., Babad, A., Lazarovitch, N., Russak, E. E. & Kurtzman, D. (2014). Nitrate leaching from intensive organic farms to groundwater. Hydrology and Earth Sys tems Science 18: 333-341. https://doi.org/10.5194/hess-18-333-2014
Da Silva, A., Suhre, E., Argenta, G., Strieder, M. & Rambo, L. (2007). Sistemas de coberturas de solo no inverno e seus efeitos sobre o rendimento de graos do milho em sucessão. Ciência Rural 37: 928-935. https://doi.org/10.1590/S0103- 84782007000400002
De Sá Pereira, E., Galantini, J., Quiroga, A. & Landriscini, M. (2014). Efecto de los cultivos de cobertura otoño invernales, sobre el rendimiento y acumulación de N en maíz en el sudoeste bonaerense. Asociación Argentina de la Ciencia del Suelo. Recuperated from https://digital.csic.es/bitstream/10261/11737/1/Connor_2005_The%20physiology%20of%20adaptation.pdf
Diacono, M. & Montemurro, F. (2010). Long-term effects of organic amendments on soil fertility. A Review. Agronomy for Sustainable Development 30: 401-422. https://doi.org/10.1051/agro/2009040
Diraman, H. & Dibeklioğlu, H. (2009). Characterization of Turkish virgin olive oils produced from early harvest olives. Journal of the American Oil Chemists’ Society 86: 663-674. doi: 10.1007/s11746-009-1392-5
Dong, S., Neilsen, D., Neilsen, G. & Fuchigami, L. (2005). Foliar N application reduces soil NO3 - N leaching loss in apples orchards. Plant and Soil 268: 357- 366. https://doi.org/10.1007/s11104-004-0333-1
Durán-Zuazo, V. H., Rodríguez Pleguezuelo, C. R., Arroyo Panadero, L., Martínez Raya, A., Francia Martínez, J. R. & Cárceles Rodríguez, B. (2009). Soil conservation measures in rainfed olive orchards in south-eastern Spain: impacts of plant strips on soil water dynamics. Pedosphere 19: 454-464. doi: 10.1016/s1002-0160(09)60138-7
Duval, M., Galantini, J., Capurro, J. & Martínez, J. (2016). Winter cover crops in soybean monoculture: effects on soil organic carbon and its fractions. Soil and Tillage Research 161: 95-105. http://dx.doi.org/10.1016/j.still.2016.04.006
Duval, M., Galantini, J., Capurro, J. & Beltran, M. (2017). Producción y calidad de diferentes cultivos de cobertura en monocultivo de soja. Ciencias Agronómicas 29: 7-13. Recuperated from https://cienciasagronomicas.unr.edu.ar/journal/index. php/agronom/article/view/212/202
Erel, R., Kerem, Z., Ben Gal, A., Dag, A., Schwartz, A., Zipori, I., Basheer, L. & Yermiyahu, U. (2013). Olive (Olea europaea L.) tree N status is a key factor for olive oil quality. Journal of Agricultural and Food Chemistry 61:11261-11272. https://doi.org/10.1021/jf4031585
Erel, R., Yermiyahu, U., Ben-Gal, A. & Dag. A. (2018). Olive fertilization under in- tensive cultivation management. Acta Horticulturae 1217: 207-224. doi: 10.17660/ ActaHortic.2018.1217.27
Fayed, T. A. (2005). Effect of some organic manures and biofertilizers on Anna apple trees. Yield and fruit characteristics. Egypt Journal of Applied Science 20: 176-191.
Fernández-Escobar, R. (2011). Use and abuse of nitrogen in olive fertilization. Acta Horticulturae 888: 249- 258. doi: 10.17660/ActaHortic.2011.888.28
Fernández-Escobar, R., Beltrán, G., Sánchez-Zamora, M. A., García-Novelo, J., Aguilera, M. P. & Uceda, M. (2006). Olive oil quality decreases with ni- trogen over-fertilization. HortScience 41: 215-219. https://doi.org/10.21273/ HORTSCI.41.1.215
Fernández-Escobar, R., Moreno, M. & García Creus. (1999). Seasonal change of mineral nutrientes in olive leaves during the alternate-bearing cycle. Scientia Horticulturae 82: 25-45. https://doi.org/10.1016/S0304-4238(99)00045-X
Fernández-Escobar, R., Ortiz-Urquiza, A., Prado, M. & Rapoport, H. F. (2008). Nitrogen status influence on olive tree flower quality and ovule longevity. Environmental and Experimental Botany 64: 113-119. https://doi.org/10.1016/ j.envexpbot.2008.04.007
Ferreira, I. Q., Arrobas, M., Claro, A. M. & Rodrigues, M. A. (2013). Soil management in rainfed olive orchards may result in conflicting effects on olive produc- tion and soil fertility. Spanish Journal of Agricultural Research 11: 472-480. doi: https://doi.org/10.5424/sjar/2013112-3501
Fuentes, M., Govaerts, B., De León, F., Hidalgo, C., Dendooven, L., Sayre, K. & Etchevers, J. (2009). Fourteen years of applying zero and conventional tillage, crop rotation and residue management systems and its effect on physical and chemical soil quality. European Journal of Agronomy 30: 228- 237. doi: 10.1016/ j.eja.2008.10.005
Giusquiani, P. L., Pagliai, M., Gigliotti, G., Businelly, D. & Benetti, A. (1995). Urban waste compost: effects on physical, chemical and biochemical soil properties. Journal of Environmental Quality 24: 175-182. https://doi.org/10.2134/jeq1995.0 0472425002400010024x
Gómez, S. A., Giráldez, J. V., Pastor, M. & Fereres, E. (1999 ). Effects of tillage method on soil physical properties, infiltration and yield in an olive orchard. Soil and Tillage Research 52: 167-175.
Gómez, J. A., Sobrinho, T. A., Giráldez, J. V. & Fereres. E. (2009a). Soil management effects on runoff erosion and soil properties in an olive grove of Southern Spain. Soil and Tillage Research 102: 5-13. doi: 10.1016/j.still.2008.05.005
Gómez, J. A., Guzmán, M. G., Giráldez, J. V. & Fereres, E. (2009b). The influence of cover crops and tillage on water and sediment yield, and on nutrient, and organic matter losses in an olive orchard on a sandy loam soil. Soil and Tillage Research 106: 137-144. doi: 10.1016/j.still.2009.04.008
Gómez, J. A., Guzmán, M. G., Giráldez, J. V. & Fereres, E. (2009b). The influence of cover crops and tillage on water and sediment yield, and on nutrient, and organic matter losses in an olive orchard on a sandy loam soil. Soil and Tillage Research 106: 137-144. doi: 10.1016/j.still.2009.04.008
Gómez-Rico, A., Salvador, M., La Greca, M. & Fregapane, G. (2006). Phenolic and volatile compounds of extra virgin olive oil (Olea europaea L. Cv. Cornicabra) with regard to fruit ripening and irrigation management. Journal of Agricultural and Food Chemistry 54: 7130-7136. doi: 10.1021/jf060798r
Gucci, R., Caruso, G., Bertolla, C., Urbani, S. Tatichi, A., Esposto, S., Servili, M., Sifola, M.I., Pellegrini, S., Pagliai, M. & Vignozzi, N. (2012). Changes of soil properties and tree performance induced by soil management in a high-density olive-orchard. European Journal of Agronomy 41: 18-27. https://doi.org/10.1016/ j.eja.2012.03.002
Gutiérrez, F., Arnaud, T. & Albi, M. A. (1999). Influence of ecological, cultivation on virgin olive oil quality. Journal of the American Oil Chemists’ Society 76: 617-621. https://doi.org/10.1007/s11746-999-0012-8
Haytova, D. (2013). A review of foliar fertilization of some vegetable crops. Annual Review and Research in Biology 3: 455-465.
Hernández, T., Chocano, C., Moreno, J. L. & García, C. (2014). Towards a more sustainable fertilization: combined use of compost and inorganic fertilization for tomato cultivation. Agriculture, Ecosystems and Environment 196: 178-184. https://doi.org/10.1016/j.agee.2014.07.006
Hussein, M. & Abd Elall, E. (2018). Effect of Macro Nutrients and Nano-Boron Foliar Application on Vegetative Growth, Yield and Fruit Quality of Manzanillo Olive. Alexandria University, Faculty of Agriculture. A. M. Balba Group for Soil and Water Research. Alexandria Science Exchange Journal 39: 394-400. doi: 10.21608/asejaiqjsae.2018.9957
Jha, P., Ram, M., Khan, M. A., Kiran, U. & Mahmooduzzafar Abdin, M. Z. (2011). Impact of organic manure and chemical fertilizers on artemisinin content and yield in Artemisia annua L. Industrial Crops and Products 33: 296-301. doi: 10.1016/j.indcrop.2010.12.011
Jiménez, B. & Carpio, A. (2008). La cata de aceites: Aceite de oliva virgen, en: Características organolépticas y análisis sensorial. Junta de Andalucía, Instituto de Investigación y Formación Agraria y Pesquera, Consejería de Agricultura y Pesca.
Jiménez Herrera, B., Rivas, A., Sánchez-Ortiz, A., Tovar, L., Luisa, M., Úbeda Muñoz, M., Callejón, R. & Ortega Bernaldo de Quirós, E. (2012). Influencia del proceso de maduración del fruto en la calidad sensorial de aceites de oliva virgen de las variedades Picual, Hojiblanca y Picudo. Grasas y Aceites 63:1-154.
Kramberger, B., Gselman, A., Janzekovic, M., Kaligaric, M. & Bracko, B. (2009). Effects of cover crops on soil mineral nitrogen and on the yield and nitrogen content of maize. European Journal of Agronomy 31: 103-109. doi: 10.1016/j.eja.2009.05.006
Kunze, A., Dalla Costa, M., Epping, J., Loffaguen, J., Schuh, R. & Lovato, P. (2011). Phosphatase activity in sandy soil influenced by mycorrhizal and non-mycor- rhizal cover crops. Revista Brasileira de Ciência do Solo 35: 705-711. Recuperated from https://www.academia.edu/55499771/Phosphatase_activity_in_sandy_soil_ influenced_by_mycorrhizal_and_non_mycorrhizal_cover_crops
Kwabiah, A. B., Stoskopf, N. C., Palm, C. A., Voroney, R. P., Rao, M. R. & Gacheru, E. (2003). Phosphorus availability and maize response to organic and inorganic fertilizer inputs in a short-term study in western Kenya. Agriculture, Ecosystems and Environment 95: 49-59. doi:10.1016/S0167-8809(02)00167-6
Larney, F. J. & Hao, X. (2007). A review of composting as a management alternative for beef cattle feedlot manure in southern Alberta, Canada. Bioresource Technology 98: 3221-3227.doi:10.1016/j.biortech.2006.07.005
Lavee, S. & Wodner, M. (2004). The effect of yield, harvest time and fruit size on the oil content in fruits of irrigated olive trees (Olea europaea), cvs. Barnea and Manzanillo. Scientia Horticulturae 99: 267-277. doi:10.1016/S0304-4238(03)00100-6 Lawson, A., Fortuna, A., Cogger, C., Bary, A. & Stubbs, T. (2013). Nitrogen contribution of rye- hairy vetch cover crop mixtures to organically grown sweet corn. Renewable Agriculture and Food Systems 28: 59- 69. doi: https://doi.org/10.1017/ S1742170512000014
Lu, H. J., Ye, Z. Q., Zhang, X. L., Lin, X. Y. & Ni, W. Z. (2011). Growth and yield responses of crops and macronutrient balance influenced by commercial or- ganic manure used a partial substitute for chemical fertilizers in an intensive vegetable cropping system. Physics and Chemistry of the Earth 36: 387-394. doi: 10.1016/j.pce.2010.03.030
Marzouk, H. A. & Kassem, H. A. (2011). Improving fruit quality, nutritional value and yield of Zaghloul dates by the application of organic and/or mineral fertilizers. Scientia Horticulturae 127: 249-254. doi: 10.1016/j.scienta.2010.10.005
Matos, L., Pereira, J., Andrade, B., Seabra. M., Beatriz, M. & Oliveira, P. (2007). Evaluation of a numerical method to predict the polyphenols content in monovarietal olive oils. Food Chemistry 102: 976-983. doi: 10.1016/j.foodchem.2006.04.026
Mazzilli, S., Kemanian, A., Ernst, O., Jackson, R. & Piñeiro, G. (2014). Priming of soil organic carbon decomposition induced by corn compared to soybean crops. Soil Biology and Biochemistry 75: 273-281. doi: 10.1016/j.soilbio.2014.04.005
Mechri, B., Tekaya, M., Hammami, M. & Chehab, H. (2019). Root verbascoside and oleuropein are potential indicators of drought resistance in olive trees (Olea europaea L.). Plant Physiology and Biochemistry 141: 407-414. https://doi.org/10.1016/ j.plaphy.2019.06.024
Mengel, K. & Kirkby, E. A. (2001). Principles of Plant Nutrition. Kluwer Academic Publishers.
Menz, G. & Vriesekoop, F. (2010). Physical and chemical changes during the maturation of Gordal Sevillana Olives (Olea europaea L., cv. Gordal Sevillana). Journal of Agricultural and Food Chemistry 58: 4934-4938. https://doi.org/10.1021/jf904311r
Mirsky, S., Ryan, M., Teasdale, J., Curran, W., Reberg Horton, C., Spargo, J., Scott Wells, M., Keene, C. & Moyer, J. (2013). Overcoming weed management challenges in cover crop–based organic rotational no-till soybean production in the eastern United States. Weed Technology 27: 193-203. doi: https://doi.org/10.1614/WT-D-12-00078.1
Morales-Sillero, A., Fernández, J. E., Beltrán, J., Jiménez, R. & Troncoso, A. (2007). Influence of fertigation in ‘Manzanilla de Sevilla’ olive oil quality. HortScience 42: 1157-1162. doi:10.21273/hortsci.42.5.1157
Morello, J., Motilva, M., Tovar, M. & Romero, M. (2004). Changes in commercial virgin olive oil (cv Arbequina) during storage, with special emphasis on the phenolic fraction. Food Chemistry 85: 357-364. doi: 10.1016/j.foodchem.2003.07.012
Palese, A. M., Vignozzi, N., Celano, G., Agnelli, A. E. Pagliai, M. & Xiloyannis, C. (2014). Influence of soil management on soil physical characteristics and water storage in a mature rainfed olive orchard. Soil and Tillage Research 144: 96-109. doi: 10.1016/j.still.2014.07.010
Pastor, M., Castro, J. Humanes, M. D. & Muñoz, J. (2000). Gestione del suolo nellólivicoltura dell´Andalusía. L´Informatore Agrario 3: 83-92.
Poffenbarger, H., Mirsky, S., Weil, R., Maul, J., Kramer, M., Spargo, J. & Cavigelli, M. (2015). Biomass and nitrogen accumulation of hairy vetch-cereal rye cover crop mixtures as influenced by species proportions. Agronomy Journal 107: 2069-2082. doi:10.2134/agronj14.0462
Porta Casanellas, J. & López Acevedo, M. (2005). Agenda de campo de suelos. Información de suelos para la agricultura y el medio ambiente. Mundi Prensa. Madrid: Spain. 541 p.
Quiroga, A., Fernández, R., Frasier, I. & Scianca, C. (2009). Cultivos de cobertura. Análisis de su inclusión en distintos sistemas de producción. En: Jornadas Nacionales: Sistemas Productivos Sustentables. Fósforo, Nitrógeno y Cultivos de Cobertura. AACS. Bahía Blanca, Argentina (https://slideplayer.es/slide/1606310/, CD).
Rani Sarker, J., Pal Singh, B., Dougherty, W., Fang, Y., Badgery, W., Hoyle, F., Dalal, R. & Cowie, A. (2018). Impact of agricultural management practices on the nu- trient supply potential of soil organic matter under long-term farming systems. Soil and Tillage Research 175: 71-81. https://doi.org/10.1016/j.still.2017.08.005
Raun, W. & Schepers, J. (2008). Nitrogen management for improved use efficiency. In: J.S. Schepers, W.R. Raun (Eds.), Nitrogen in Agricultural Systems. (pp. 675- 693). Madison: American Society of Agronomy. https://doi.org/10.2134/agron- monogr49.c17
Reicosky, D. & Archer, D. (2005). Cuantificación agronómica del aumento de material orgánica del suelo en siembra directa. En: XIII Congreso AAPRESID. Rosario Santa Fé. 9-12 agosto.
Restovich, S., Andriulo, A. & Amémdola, C. (2011). Introducción de cultivos de cobertura en la rotación soja-maíz: efecto sobre algunas propiedades del suelo. Revista de la Asociación Argentina de la Ciencia del Suelo 29: 61-73.
Rezk, A., Nofal, O. & El Nasharty, A. (2008). Improving yield and quality of some olive cultivars using an integrated and balanced fertilization program grown in calcareous soil. Alexandria Science Exchange Journal 29: 217-222. doi: 10.21608/ ASEJAIQJSAE.2008.3201
Rimski Korsakov, H., Alvarez, C. & Lavado, R. (2015). Cover crops in the agricultural systems of the Argentine Pampas. Journal of Soil and Water Conservation 70: 134-140. doi:10.2489/jswc.70.6.134A
Rodrigues, M., Ferreira, I., Claro, A. & Arrobas, M. (2012). Fertilizer recommendations for olive based upon nutrients removed in crop and pruning. Scientia Horticulturae 142: 205-211. https://doi.org/10.1016/j.scienta.2012.05.024
Rodrigues, M., Pavão, F., Lopes, J., Gomes, V., Arrobas, M., Moutinho Pereira, J., Ruivo, S., Cabanas, J. & Correia, C. (2011). Olive yields and tree nutritional status during a four-year period without nitrogen and boron fertilization. Communications in Soil Science and Plant Analysis 42: 803-814. doi: 10.1080/00103624.2011.552656
Romero, P., Castro, G., Gómez, J. A. & Fereres, E. (2007). Curve number values for olive orchards under different soil management. Soil Science Society of America Journal 71: 1758-1769. https://doi.org/10.2136/sssaj2007.0034
Rotondi, A., Bendini, A., Cerretani, L., Mari, M., Kercker, G. & Gallina Toschi, T. (2004). Effect of olive Ripening Degree on the Oxidative Stability and Organoleptic Properties of Cv. Nostrana di Brisighella Extra Virgin Olive Oil. Journal of Agricultural and Food Chemistry 52: 3649-3654. doi: 10.1021/jf049845a
Roussos, P. A., Gasparatos, D., Kechrologou, K., Katsenos, P. & Bouchagier, P. (2017). Impact of organic fertilization on soil properties, plant physiology and yield in two newly planted olive (Olea europaea L.) cultivars under Mediterranean conditions. Scientia Horticulturae 220: 11-19. http://dx.doi.org./10.1016/ j.scientia2017.03.019
Rueda, G. (2016). El aceite de oliva del SOB genera alrededor de U$S 14 millones/año. Diario La Nueva Provincia, Bahía Blanca-Argentina. Recuperated from https://www.lanueva.com/nota/2016-8-6-7-46-0-el-aceite-de-oliva-del-sob-genera- alrededor-de-u-s-14-millones-ano
Sánchez Casas, J., De Miguel, C., Osorio, E., Marín, J., Gallardo, L. & Martínez, M. (2006). Calidad sensorial de aceites de oliva virgen procedentes de variedades de aceitunas producidas en Extremadura. Grasas Aceites 57: 313-318. http://dx.doi. org/10.3989/gya.2006.v57.i3.54
Sánchez-García, M., Sánchez-Monedero, M. A., Roig, A., López-Cano, I., Moreno, B., Benítez, E. & Cayuela, M. L. (2016). Compost vs biochar amendment: A two- year field study evaluating soil C build-up and N dynamics in an organically managed olive crop. Plant and Soil 408: 1-14. doi: 10.1007/s11104-016-2794-4. Sá Pereira, E. (2013). Los cultivos de cobertura y la productividad del maíz en siembra directa: dinámica del nitrógeno, agua y fracciones orgánicas del suelo. (Doctoral Thesis), Universidad Nacional del Sur, Argentina.
Schipanski, M., Barbercheck, M., Douglas, M., Finney, D., Haider, K. & Kaye, J. (2014). A framework for evaluating ecosystem services provided by cover crops in agroecosystems. Agricultural Systems 125:12-22. doi:10.1016/j.agsy.2013.11.004
Spargo, J., Cavigelli, M., Mirsky, S., Meisinger, J. & Ackroyd, V. (2016). Organic supplemental nitrogen sources for field corn production after a hairy vetch cover crop. Agronomy Journal 108: 1992-2002. https://doi.org/10.2134/ agronj2015.0485
Steve, D. (2009). Sustainable farming compost tea. Cited in http://www.soilsoup.com
Strudley, M. W., Green, T. R. & Ascough, L. l. (2008). Tillage effects on soil hydraulic properties in space and time: state of the science. Soil and Tillage Research 99: 4-48. doi:10.1016/j.still.2008.01.007
Teasdale, J., Mirsky, S., Spargo, J., Cavigelli, M. & Maul, J. (2012). Reduced-tillage organic corn production in a hairy vetch cover crop. Agronomy Journal 104: 621-628. doi:10.2134/agronj2011.0317
Tekaya, M., Mechri, B., Bchir, A., Attia, F., Cheheb, H., Daassa, M. & Hammami, M. (2013). Enhancement of antioxidants in olive oil by foliar fertilization of olive trees. Journal of the American Oil Chemists’ Society 90: 1377-1386. doi: 10.1007/ s11746-013-2286-0
Tekaya, M., Mechri, B., Cheheb, H., Attia, F., Chraief, I., Ayachi, M., Boujneh, D. & Hammami, M. (2014). Changes in the profiles of mineral elements, phenols, tocopherols and soluble carbohydrates of olive fruit following foliar nutrient fertilization. LWT-Food Science and Technology 59: 1047-1053. doi: 10.1016/ j.lwt.2014.06.027
Therios, I. (2009). Mineral nutrition of the olive. In: CAB International (Ed.), Olives. United Kingdom (pp. 179-209). UK: CAB International.
Tiecher, T., Rheinheimer dos Santos, D. & Calegar, A. (2012). Soil organic phosphorus forms under different soil management systems and winter crops, in a long-term experiment. Soil and Tillage Research 124: 57-67. doi: 10.1016/ j.still.2012.05.001
Tirol-Padre, A., Ladha, J. K., Regmi, A. P., Bhandari, A. L. & Inubushi, K. (2007). Organic amendments affect soil parameters in two long-term rice-wheat experiments. Soil Science Society of America Journal 71: 442-452. doi: 10.2136/ss-saj2006.0141
Tosti, G., Benincasa, P., Farneselli, M., Pace, R., Tei, F., Guiducci, M. & Thorup Kristensen, K. (2012). Green manuring effect of pure and mixed barley–hairy vetch winter cover crops on maize and processing tomato N nutrition. European Journal of Agronomy 43: 136-146. doi: 10.1016/j.eja.2012.06.004
Vega, V., Hidalgo, J. C. & Hidalgo, J. (2018). Fertilización mineral del olivar. Recuperated from https://www.interempresas.net/Grandes-cultivos/Articulos/217394- Fertilizacion-mineral-del-olivar.html
Vincenzo, V., Caro, A., Poiana, M. & Piga, A. (2006). Effect of storage period and exposure conditions on the quality of Bosana extra virgin olive oil. Journal of Food Quality 29: 139-150. doi:10.1111/j.1745-4557.2006.00062.x
Whalen, J. K., Hu, Q. & Liu, A. (2003). Compost applications increase water-stable aggregates in conventional and no-tillage systems. Soil Science Society of American Journal 67: 1842-1847. https://doi.org/10.2136/sssaj2003.1842
Xiloyannis, C., Martínez Raya, A., Kosmas, C. & Favia, M. (2008). Semi-inten- sive olive orchards on sloping land: Requiring good land husbandry for future development. Journal of Environmental Management 89: 110-119. doi: 10.1016/ j.jenvman.2007.04.023
Youssef, N., Zarrouk, W., Carrasco Pancorbo, A., Ouni, Y., Segura Carretero, A., Fernández Gutiérrez, A., Daoud, D. & Zarrouk, M. (2010). Effect of olive ripeness on chemicals properties and phenolic composition of chetoui virgin olive oil. Journal of the Science of Food and Agriculture 90: 199-204. doi: 1/0.1002/jsfa.3784