Over two million tonnes of fertiliser are applied to New Zealand pastures and crops annually and there is an increasing desire by farmers to ensure that the best possible economic return is gained from this investment. Spreading distribution measurements undertaken by Lincoln Ventures Ltd (LVL) have identified large variations in the evenness of fertiliser application by spreading machines which could lead to a failure to achieve optimum potential in some crop yields and to significant associated economic losses. To quantify these losses, a study was undertaken to calculate the effect of uneven fertiliser application on crop yield. From LVL's spreader database, spread patterns from many machines were categorised by spread pattern type and by coefficient of variation (CV). These patterns were then used to calculate yield losses when they were combined with the response data from five representative cropping and pastoral situations. Nitrogen fertiliser on ryegrass seed crops shows significant production losses at a spread pattern CV between 30% and 40%. For P and S on pasture, the cumulative effect of uneven spreading accrues, until there is significant economic loss occurring by year 3 for both the Waikato dairy and Southland sheep and beef systems at CV values between 30% and 40%. For nitrogen on pasture, significant loss in a dairy system occurs at a CV of approximately 40% whereas for a sheep and beef system it is at a CV of 50%, where the financial return from nitrogen application has been calculated at the average gross revenue of the farming system. The conclusion of this study is that the current Spreadmark standards are a satisfactory basis for defining the evenness requirements of fertiliser applications in most circumstances. On the basis of Spreadmark testing to date, more than 50% of the national commercial spreading fleet fails to meet the standard for nitrogenous fertilisers and 40% fails to meet the standard for phosphatic fertilisers.Keywords: aerial spreading, crop response, economic loss, fertiliser, ground spreading, striping, uneven application, uneven spreading, yield loss
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