Economic viability, energy and nutrient balances of site-specific fertilisation for citrus

Core objectives of precision agriculture are to improve the economic and environmental performance of agricultural systems. This study used a long-term experiment in citrus to assess whether site-specific nutrient management was successful from these two perspectives. Variable and uniform rate fertilisation treatments were implemented in intercalated strips across two 25 ha citrus groves in Sao Paulo state, Brazil. To generate variable rate recommendations, information from soil fertility and yield maps were fed into a traditional recommendation formula used by growers. The experiment was carried out for five growing seasons. An economic, energy and nutrient balance analysis was conducted. Variable rate application increased average yield in grove 1 but sometimes reduced yield in grove 2. As a consequence, profit was increased by 34.7% (US$* 318.5 ha(-1) year(-1)) in grove 1. In grove 2, profit was reduced by 8.5% (US$ -97.4 ha(-1) year(-1)). Embodied fertiliser energy was reduced by 34% in grove 1 and by 29% in grove 2. Nutrient surplus after harvest was reduced by approximately 20-70% depending on the nutrient. Maps of economic and environmental indicators showed that site-specific management did not reduce the spatial variability of the system's performance. The variable rate strategy tested could be improved by using local decision rules rather than generalised recommendation formulas. Site-specific analysis of profit, embodied energy and nutrient balance help to assess system performance and can potentially improve decisions in site-specific nutrient management. (C) 2020 IAgrE. Published by Elsevier Ltd. All rights reserved.