Assessment of Some Spatially Variable Soil Factors Limiting Crop Yields

Keywords: Soil phosphorus, Soil potassium, Subsoil loosening, Soil mapping, Deep incorporation, Root activity, Spatial variability.

Crop quality and marketability often reflect the uniformity of growth within a field and uniform crops often use inputs very efficiently and speed harvest. Within-field variation in growth and yield has long been recognised. In the past it has been measured at considerable cost. Frequently, considerable variation was observed between years and crops in the position of high and low yielding areas. Thus seeking the causes of yield variation was difficult, and even if identified, varying husbandry practices to allow for variable yields was too complicated in practice.

The introduction of fully automatic and integrated yield mapping systems can now generate information showing the variation in crop performance and yield within individual fields and this now adds a new dimension to the management opportunities for arable agriculture. These new opportunities for precision farming, defined here as spatially variable management within a field, will allow more efficient use of inputs, greater profitability and more environmentally benign husbandry. But optimising the opportunities now available will require that the causes of yield variation are ascertained and appropriate remedial measures are available.

Yield variation can be caused by within-field differences in any of those factors which contribute to the biological, chemical and physical properties of soil and ascertaining the effect of these factors is often made more difficult because they interact one with another. Biological factors are not discussed here but some chemical and physical soil parameters are. Many of these factors which affect yield act through their effects on water and nutrient acquisition by plant roots. Examples of some critical values for soil parameters are given and related to the distribution and function of roots.

A E Johnston, P B Barraclough and P R Poulton, IACR-Rothamsted, Harpenden, Hertfordshire, UK

C J Dawson, Chris Dawson & Associates, Strensall, York, UK

48 pages, 15 figures, 9 tables, 90 refs.