Over the past decade the national average wheat yield has remained relatively static at around 8.5 t/ha. However, set this against the biophysical potential of wheat at 19t/ha and the UK's highest recorded wheat yield of 16.52 t/ha back in 2015, and there is clearly a realistic opportunity to improve yields on farm.
But, how can this be achieved?
Crop yields are directly affected by weather, nutrition and disease, but other contributing factors often overlooked are soil health and quality. The chart opposite illustrates the point – with crop inputs of seed, fertiliser & spray constant, factors such as compaction, poor drainage, pH and poor nutrient availability quickly compound to reduce final yield.
Soil quality neatly divides into three broad categories encompassing the physical, chemical and biological constituents of the soil.
Physical measurements
These include soil texture; defining the amount of sand silt and clay in each sample. This is useful to understand how drought-prone a soil would be and how easy it would be to cultivate.Soil structure investigations highlight areas of compaction, indicating how well crop roots have developed. Finally, soil density also highlights the amount of compaction which is important in terms of soil drainage and root development.
Chemical measurements
These illustrate the nutritional state of the soil. Plants need the availability of 17 nutrients to grow, four of which are major nutrients (N, P, K and Mg) and the remaining 13 are micronutrients such as copper (Cu) and zinc (Zn) etc. The most important measurement in the chemical suite is pH. It is that which controls the availability of the nutrients –major nutrients are more available in a high pH soil and micronutrients become available in a low pH soil.
Biological measurements
These have become more popular, with earth worm counts often used as a measure of soil quality. However, there are many more organisms living in the soil breaking down old crop residue, restructuring the soil and releasing soil nutrients to the plants. A useful way to evaluate the overall amount of biological activity is to measure the volume of carbon dioxide respired by the micro-organisms, which can be achieved by sealing a soil sample for 24 hours.
Organic matter
There is one other component of soil which is inextricably linked to all three soil quality categories. The benefits of organic matter (OM) cannot be understated, as its presence in soils helps to improve workability, drainage and aeration. OM can hold on to nutrients in soil textures which are liable to leaching and provide a sustainable food source for the microorganisms.With such tangible benefits, it makes sense to map the OM quantities across the farm to determine what the current levels are. If they are low, deduce which fields would benefit first from manures or cover crops.
OM mapping can be cost-effective if carried out at the same time the field is sampled for potash, and typically costs £20 per field.
Combining all of the soil quality measurements into a single report is the best way to identify underlying issues which may potentially be limiting the yield on farm.
If you are interested in more information please ask your local SOYL manager for further details.
David Whattoff
Agricultural Development Manager
For specific advice for your business related to this blog or any other aspect of precision crop production get in touch with SOYL.