Regional research into optima rates

Nitrogen fertiliser is an integral application in cotton growing, and its ultimate effect on yield is being quantified through industry-wide trials to help growers make more informed decisions about rates and timing of application. Nitrogen trials undertaken by CottonInfo Regional Development Officers in crops across cotton growing regions showed that increasing rates of nitrogen (N) fertiliser didn't always correlate to higher yields. Further data from CSD variety trials and the Crop Consultants Australia annual survey show that percentage yield increases are not in line with rising N fertiliser application rates. While much research has been undertaken around nitrogen use in cotton growing, there is still a lot of uncertainty regarding optimal rates, with most growers more likely to apply "more than is needed" than "not enough" at the risk of compromising yield. This approach can lead to an overall reduction in Nitrogen Fertiliser Use Efficiency (NFUE), which is the ratio of lint yield removed for each kilogram of N applied. But what is needed by the crop to achieve maximum yield and what denotes "not enough"? How much influence does the rate and timing of the application have on yield?