Reasons for predicting the productivity of organic grassland

Before considering methods available for predicting yield from grassland, it is useful to consider why an accurate prediction is important. The main reason is that there is at least a fourfold differ- 

The second important point is that although factors that affect herbage production, such as climate, latitude and aspect, are outside the farmer s control, other factors, such as soil nutrient level and grazing management, can be controlled by the skilful farmer. 

The third important factor is that the method of prediction should not be so expensive that the farmer is unlikely to want to pay for the answer, as might be the case if the prediction had to depend on a whole series of detailed laboratory analyses. 

Finally, there is the question of the accuracy of the prediction. It is highly likely that any increase in accuracy will also increase the cost. For a start, the smallest animal likely to be used in grazing is a sheep, which will consume 0.5 t of dry matter per annum. This means that there is little point in trying to predict within less than 0.5 t of dry matter. With an all-dairy farm, accuracy can be less precise, because a dairy cow is likely to eat 4.2 t of dry matter per head per annum. 

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