Estimation of Yield of Silage Maize Dry Matter from Volume Harvested or by Sampling Harvested Trailer Loads

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Abstract Determination of the dry matter yield of a silage maize crop involves weighing the total crop. This is expensive and time-consuming. But the dry matter yield of a crop of silage maize can be calculated from the volume of the harvested material and the dry matter density; the latter is defined as kg of dry matter/m 3 of freshly harvested material in a trailer. To test the accuracy of this procedure the value of the dry matter density of silage maize in a trailer at harvest and the factors influencing this density were studied. In 1979, 1980 and 1986, data were collected from 423 trailer loads of maize. The standard deviation of the dry matter density of a random load of maize in a trailer was 11·2kg/m3. The 95% confidence interval was 112±22·5kg/m 3 . Of the variance of the dry matter density, 40% was attributable to differences between years, 34% to differences between fields within a year, 12% to differences between trailers within a field and 14% to differences between loads of maize within a trailer. Neither the dry matter content of the maize nor the height of the maize in the trailer were useful for predicting the dry matter density. This density was not affected by brand or type of field chopper, chopping length or the use of a kernel crusher. The way in which the trailer was filled had a small (2 to 3%) effect on the dry matter density. The dry matter density of a crop of maize can be estimated by measuring it in a sample consisting of one or more trailer loads. When the dry matter density of a single load of maize was measured, the limits of the 95% confidence interval were ±10·5% of the mean dry matter density; for a sample consisting of 10 loads of maize the limits of the 95% confidence interval were ±3·3% of the mean. The dry matter density of silage maize in a trailer correlated ( r 2 = 0·58) with the dry matter density in a 301 container. Further research is needed to reveal whether the dry matter density in such a container allows a reliable prediction of dry matter density in a trailer.