Nutrient use efficiency of citrus orchards in South Africa with different fertilisation and irrigation management approaches

Rational use of natural resources and inputs entails an improvement or maintenance of a high nutrient use efficiency (NUE) without an adverse impact on profitability. In this study, the NUE of low-delivery-rate drip irrigation/fertilisation (LowFlow) systems, conventional drip irrigated/fertigated (DripFert), micro-irrigated/fertigated (MicroFert) and micro-irrigated/granular fertilised (MicroGran) systems in four climatic regions of South Africa were compared using different NUE indices. In the LowFlow system, an average of only 45% of the applied N was removed by the crop over all the regions, whereas it was 80% and 75% for the MicroFert and MicroGran production systems, respectively. Poor NUE was ascribed to excessive fertilisation rates, particularly in LowFlow and Western Cape orchards. South African benchmark NUEs for input nutrient quantities per tonne of fruit produced were subsequently proposed: nitrogen (1.70–2.20 kg N t−1), phosphorus (0.18–0.28 kg P t−1) and potassium (1.56–1.90 kg K t−1). In the context of environmental responsibility and economic sustainability, the South African citrus industry can benefit from prescriptive NUE benchmarks. Observations regarding variability in soil and leaf samples taken in close proximity were also made, resulting in recommendations to avoid errors when fertilisation recommendations are prepared.