Evaluation of residual values of different fertilisers at various rates used in phosphorus recapitalisation of an acid tropical soil

Abstract

AbstractThe success of ‘phosphorus (P) recapitalisation’ depends on the changes in residual value (RV) over time. RVs of triple superphosphate (TSP), Gafsa phosphate rock (GPR) and Christmas Island phosphate rock (CIPR) were determined with and without manure bimonthly for 14 months. RV was calculated as the amount of previously applied fertiliser required to produce yield X divided by the amount of freshly applied TSP required to produce the same yield. Dry matter yield (DMY) response curves were curvilinear, with maximum DMY (11 t ha−1) occurring between 150 and 200 kg P ha−1 at 6 months and declining with time to 2–4 t ha−1 (14 months). Manure/fertiliser combinations increased DMY for CIPR but depressed DMY for TSP and GPR in all harvests except the first one. This can be attributed to nutrient imbalance caused by high P levels. RVs declined with time for fertilisers alone from 100–140% to 10–20% (14 months), while for fertiliser/manure combinations they declined from 110–180% to 10–20% (14 months). Increasing P rates from 100 to 300 kg P ha−1 resulted in the depression of initial RVs (100–140%) to 20–60% and later to 10–20% (14 months). Therefore P recapitalisation was not beneficial and hence annual P application would be recommended at 100–150 kg P ha−1. The phosphate rocks could effectively substitute for TSP.Copyright © 2006 Society of Chemical Industry