Accelerated testing of nutrient release rates from fertiliser granules

A method is developed for estimation of accelerated nutrient release rates into a soil from particulate fertiliser formulations, by carrying out release studies at elevated temperatures. This can provide time-saving targetting of samples to be subsequently used in field trials. The rate of total phosphorus leaching into water from a standard commercial fertiliser product embedded in grey, deep, sandy duplex soil was monitored using inductively coupled plasma-optical emission spectroscopy. The time dependence of phosphate concentration at a given temperature was found to obey simple first- order kinetics. These data fitted an Arrhenius relation within acceptable limits, enabling release rates at ambient field temperatures to be estimated significantly faster than by field experiment. A release rate calculated for the accelerated test, i.e. (1.2 ± 0.1) x [10.sup.-3]/min, when compared with a more standard-type pot-trial leaching rate for the corresponding temperature of 2.3 x [10.sup.-4]/min, gives a direct correlation of ~1 : 1 when corrected for concentration differences. Additional keywords: Arrhenius, ICP-OES, leaching, kinetics, phosphate, soil.
Introduction Fertiliser loss to soil water seepage and surface runoff not only results in wastage of fertiliser resources but also contributes to algal blooms and eutrophication. In coastal waters, this [...]