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Accelerated testing of nutrient release rates from fertiliser granules

Warrender, Cristy M., Warrender, Garry W., Smith, Bradley, McKenzie, Colin, Gilbert, Robert G.
Soil research 2010 v.48 no.8 pp. 668-673
field experimentation, granules, leaching, phosphates, phosphorus, soil, spectroscopy, temperature
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)×10⁻³/min, when compared with a more standard-type pot-trial leaching rate for the corresponding temperature of 2.3×10⁻⁴/min, gives a direct correlation of ~1:1 when corrected for concentration differences.