NUTRIENT FLUXES IN KIWIFRUIT ORCHARDS

Understanding the cycling of nutrients at the orchard ecosystem scale and quantifying their fluxes between different compartments are important steps for a sustainable management of fertilization allowing improvements of the use efficiency of internal resources and a reduction of both the need for external fertilizer and the losses of nutrients from the system. This paper discusses approaches used to study biogeochemical cycles at the orchard scale, exemplified by specific data on kiwifruit from the literature. The focus is on methodological aspects as well as on the potential use of results. Major fluxes of macronutrients considered are 1) uptake and partitioning; 2) cycling within the plant; and 3) soil return of nutrients during decomposition of vine litter. Soil nutrient uptake and partitioning within vines are assessed by excavation of plants and data on biomass of pruned wood, abscised leaves and fruit as well as their nutrient concentrations. Internal cycling studies have been focussed mainly on nitrogen because of the availability of the stable isotope ¹⁵N and have addressed the storage and remobilization processes between subsequent years as well as recycling between leaves and roots within a single season. Nutrient release from decomposing leaves and prunings was studied using the litter bag technique and ¹⁵N labelled material. Data on nutrient fluxes should be integrated in a model to predict fertilizer needs and the fate of internal and exogenous nutrients.