Variable rate fertilization in citrus: a long term study

Variable rate technology allows application of inputs according to the field spatial variability. Citrus fields can be significantly variable in either soil or plant aspects. Thus, variable rate fertilization seems to be an adequate approach to deal with this issue. However, its effects on input consumption, yield and other crop factors have not yet been assessed during long term experiments. The objective of this study was to evaluate the effects of variable rate fertilization on the input consumption, soil fertility and yield during a long term experiment in citrus. A strip experiment was established in two 25 ha citrus fields in Sao Paulo, Brazil, to compare variable rate against uniform rate fertilization. This experiment was carried out during 6 years. Variable rate prescriptions were based on soil and leaf grid sampling and on yield maps. Uniform applications were based on conventional soil sampling and average yield data. Variable rate treatment resulted in significant reduction in input consumption, but different soil fertility and yield responses were obtained by the variable rate in each field. Field 1 presented higher variability regarding soil and topography. Variable rate application resulted in a better soil fertility management and yield increase in this field. Field 2, which was less variable regarding soil and topography, got poorer results from variable rate treatment regarding soil fertility and yield response. Either way, variable rate technology resulted in higher fertilizer agronomic efficiency in both fields. N, P, and K fertilizers resulted in more fruit yield when applied site-specifically.