Resources management in fruit tree orchards for low carbon and water footprints

Over the past six decades a large proportion of agricultural land has been degraded (erosion, loss of organic matter, salinization, etc.) by over-exploitation and excessive external input (chemical fertilizers, unsuitable irrigation methods, application of low-quality water, soil tillage, etc). The emission of greenhouse gases from agriculture currently accounts for 10-12% of total anthropogenic emissions. Increasing consumer demand for low C-footprint food has encouraged the industry to find ways to reduce energy input throughout the production-supply chain. At orchard scale, some operations (use of machines, fertilization, irrigation, etc) are CO2 sources, while the total carbon balance can be negative (sink) or positive (source) depending on soil and canopy management strategies. Agricultural systems that use non-sustainable techniques can aggravate the current situation. While such practices are still common among growers, there is ample evidence that good practices can restore organic matter levels in soil, reduce erosion and environmental pollution and increase CO2 sequestration from the atmosphere into the soil . A good fertilization plan should take into account plant demands, availability of mineral elements in the soil (mineralization process) and other inputs, particularly in the water used for irrigation, in order to avoid water and soil contamination and improve yield quality and quantity. Environmentally-friendly techniques also have positive effects on soil microbiota, enhancing soil fertility, plant growth, yield and quality. Sustainable orchard management is of particular importance in Mediterranean climates, where there is a high rate of soil mineralization, low rainfall, high evapotranspiration and often little water available for irrigation. The soil can store large amounts of rainwater, particularly in autumn and winter when plant water needs are very low. Deep loamy soils can hold up to 2.000 m3 ha-1 , assuming a root depth of 1m. The water contained in this volume of soil can satisfy 30-40% of the yearly water requirements of an orchard in semi-arid regions. Soil management under conditions of water scarcity should aim to improve water-holding capacity by increasing organic matter levels and hydraulic conductivity, and to eliminate or reduce evaporation. Orchard design, canopy architecture and correct management of the latter must also be addressed to improve not only water use efficiency (by increasing the exposed/shaded leaves ratio) but also microclimatic conditions inside the canopy, and therefore bud, flower and fruit quality. Efficiency can be increased by reducing tree size, adopting training systems that maximise the number of exposed leaves, minimising shading, and performing summer pruning. Exposure to light and high evapotranspiration improves the quality and taste of fruit, increases accumulation of less-mobile mineral nutrients (such as calcium) and enhances accumulation of reserve substances in wood and in flower buds and therefore flower quality.