Etridiazole may conserve applied nitrogen and increase yield of irrigated cotton

Abstract

Recovery of applied N is often poor in irrigated cotton production in Australia, due to N loss through biological denitrification in the heavy clay soils. We envisaged that the N loss through denitrification could be reduced by limiting the soil nitrate concentration by applying a nitrification inhibitor with the fertilizer. We applied the nitrification inhibitor etridiazole in three field experiments in two cotton-growing seasons (1991-1993). The nitrification of ammonium-N applied as urea or anhydrous ammonia, the cotton crop N uptake and lint yield were monitored; recovery of 15N-labelled urea applied to microplots was assessed at crop maturity. In the first experiment, urea was applied at rates of 0 and 80 kg N ha-1 with etridiazole (applied as Terrazole EC). The recommended etridiazole rate (300 g ha-1) was compared with nil, half and double that rate. In the fertilized treatments where etridiazole was applied, nitrification of ammonium was retarded for more than 2 months, cotton crop N uptake was increased by 28% at maturity and lint yield increased by 18%, relative to the control. Etridiazole application had little effect on soil N concentrations, crop N uptake or lint yield in the unfertilized treatments. Fertilizer recovery was significantly improved from 35 to 50% with etridiazole application. The second experiment (in the following year) was conducted under commercial conditions. Etridiazole was applied with urea at 86, 119 and 154 kg N ha-1. As in Experiment 1, nitrification was delayed, crop N uptake was enhanced at crop maturity and lint yield was significantly increased by 46 kg ha-1 (3% greater than the control) with etridiazole application. In the third experiment, anhydrous ammonia was applied at rates from 0 to 175 kg N ha-1, with and without etridiazole. Recovery of 15N-labelled urea was not significantly altered by etridiazole application from the relatively high (69%) recovery in the control treatment. Maximum lint yield was 130 kg ha-1 (6.9%) higher in the etridiazole treatments, but required the application of additional N to achieve it. These experiments indicated that etridiazole was cost-effective in increasing lint yield of irrigated cotton and conserved applied N where substantial denitrification loss occurred.