Soil - the life support system

It is right that soil should be the subject of an early chapter in my recently published book, Farming with the Environment – Thirty Years of Allerton Project Research. The health of our soil literally and metaphorically underlies the ecosystem on which we all depend. Not least, it is fundamental to farming.

Almost by definition, soil health is dependent on biological activity and much of our research over the years has focused on life in the soil, the role it performs, and the influences on it. Earthworms, collembola and microbial fungal and bacterial communities all perform important functions, and the soil also supports larval and pupal stages of many invertebrates that are predators or parasitoids of crop pests.

We have found that physical properties, especially compaction of our clay soils, reduce biological activity and abundance of some earthworms and other invertebrates. We have demonstrated that compaction limits water infiltration rates, contributing to surface runoff and loss of soil and nutrients to water. Using our Gasmet multi-gas analyser, we have found that emissions of nitrous oxide, a greenhouse gas with three hundred times the global warming potential of carbon dioxide, are substantially higher from compacted soils than well-structured direct drilled land. In a direct drilled system, sub-soiling alleviates this problem without the negative impacts on soil function associated with the more traditional approach of ploughing.

Soil organic carbon also influences soil biology and water infiltration rates. Comparing plough and direct drilled plots, our research reveals that microbial activity and diversity, and associated CO2 emissions are higher in the latter but that direct drilled plots are also associated with higher soil carbon. We are continuing to explore this apparent anomaly. We have also explored the influence of reduced cultivations on surface runoff and loss of sediment and nutrients from arable land.

We have found that cover crops intended to reduce soil and nutrient loss before spring crops can have some benefits in supressing weeds and encouraging earthworms, with subsequent benefits to cropping, but only where cover crop establishment is really good, and this can be challenging on clay soils. If not managed too intensively, some modern deep-rooting grass cultivars have the potential to sequester carbon in a stable form below the plough layer, and to increase water infiltration rates, contributing to catchment scale targets for water quality and flood risk management.

Such wider benefits, extending far beyond the soil at the field scale, also include positive contributions to terrestrial biodiversity within farming systems, a topic covered in the next chapter of the book.