The evaluation of a controlled release nitrogen fertiliser

Abstract

Experiments in the laboratory, glasshouse and in the field assessed the chemical and agronomic characteristics of four polymer-coated urea products manufactured to different specifications, by altering the number and chemical nature of the coatings. (The chemical and physical nature of the coatings and the coating process are the property of the New Zealand distributor, Eko 360 Ltd.) They are claimed to be controlled release nitrogen (N) fertilisers. The N release characteristics of the experimental products were measured, relative to water soluble urea, in the laboratory in the absence of soil. These results confirmed that the N release rates were consistent with the distributor's specifications and were slower than urea. A glasshouse experiment was designed to use N uptake by ryegrass as a proxy for the N release rate in a soil. These results confirmed those from the laboratory, indicating that soil had little effect on the relative N release characteristics of the fertilisers. The experimental product with the slowest release rate was selected for evaluation in the field. In three field experiments the effect the experimental product, applied once at two rates, on pasture production was compared with the same rates of N applied once as urea, over 5-6 months. The experimental product tested increased N use efficiency (NUE, kg DM/kg N applied) by between 5-50% depending on the site and rate of N application. Thus it is concluded that the products are as claimed - contolled release N fertilisers, relative to urea - and that this characteristic is expressed under field conditions. Proof-of-concept was therefore established. Keywords: fertiliser, nitrogen, nitrogen use efficiency, pasture, SmartFertTM, urea