Costs and Effects of Uneven Spreading of Nitrogen Fertilisers

Keywords: Fertiliser spreading, uniformity, coefficient of variation, CoV, financial losses, spread pattern, measurement.

The distribution patterns of solid fertilisers applied by different types of spreader can be measured in specialised test halls, using floor mounted trays within a building or using trays in field conditions. The resulting distribution will depend on the basic underlying distribution pattern obtained with a particular mechanism design operating with a given material but will also be influenced by the conditions at the time of the test and the sampling arrangements used. The results in this paper indicate that the coefficient of variation (CoV) of a lapped distribution pattern is an appropriate measure of the uniformity obtained and that this can be related to the financial loss incurred by a lack of uniformity in a way that does not show bias to the results for a given form of basic distribution pattern. A series of spread patterns were generated theoretically based on four basic distribution types that were varied by including some systematic error that could be related to the practical operation of different spreader designs. A random noise element was also included the distribution. For each theoretical distribution a coefficient of variation was calculated and an associated financial losses determined by using a nitrogen response relationship obtained for a third wheat crop from field trials data. Financial losses were shown to be a function of the coefficient of variation squared for the winter wheat crop and with similar power law relationships for other crops. Therefore financial losses due to the uneven spreading of nitrogen fertilisers could be estimated from measurements of the coefficient of variation of a distribution pattern. Using a range of nitrogen response characteristics, losses in a winter wheat due to poor spreading were estimated to be up to £16.60/ha for distributions where striping was unlikely to be visible in a winter cereal crop. It was recognised that the loss figures obtained were a function of the nitrogen response characteristics used and the value of the crop produced and that there is now scope for an up-dated analysis accounting for current trends.

Paul C H Miller, Silsoe Spray Applications Unit, The Arable Group, Wrest Park, Silsoe, Bedford MK45 4HP, UK.

Eric Audsley, Cranfield University, Cranfield, Bedfordshire MK43 0AL, UK.

Ian R Richards, Ecopt, Dewells Farm House, Ufford Road, Bredfield, Suffolk IP13 6AR, UK.

24 pages, 13 figures, 13 tables, 9 references.