Soil health

Soil structure types can be described in many ways (Figure 1). However they can be grouped into three main groups: 1) those that are formed biotically by the soil biology and organic matter often seen around the roots of cover crops; 2) those that are formed abiotically, for example through the action of tillage or cracking in a dry summer; and 3) those that are formed by compaction, often seen by horizontal platy structures in the soil profile.

Soil structure needs to be resilient in an agricultural production system throughout the cropping period and beyond. Only too often soil structure “looks” good immediately behind a tillage operation, only to deteriorate once heavy rains appear and that same structure starts to collapse due to overworking of the soil, which can eventually end up as a “sloppy mess”.

Figure 2 shows large differences in soil structure in adjacent plots that have been managed in different ways, including with cover cropping.

One of the core principles of regenerative agriculture is to keep a living root in the ground at all times. Cover Crops fulfil this role between harvest and establishment of a spring crop. The Cover Crop has many benefits to soil health, including maintaining aggregation of soil particles, feeding the soil flora and fauna and aiding drainage by putting down roots.

The structure of soil is hugely complex, fragile, and variable over many different soil texture types, horizons, geographic locations, and climates. It comprises the physical habitat of soil living organisms, and controls many important physical, chemical, and biological soil functions and associated ecosystem services.

It is a key component of the quality and health of agricultural soils worldwide and different agricultural practices play a significant part in its sustainability and resilience, with cover crops being particularly beneficial.

Typically soil structure can, for example, be damaged by compaction and over disturbance (Tillage) or improved by planting cover crops and eliminating or reducing soil disturbance (Figure 3, below).

Fundamentally good healthy soil structure can be thought of the degree to which the pedogenic process called aggregation, which forms because of the rearrangement, flocculation and cementation of soil particles, occurs which is facilitated by a plethora of soil biological and organic matter activity.

In some cases, grazing cover crops has been shown to improve the cycling of their nutrients, making some nutrients more available to the following crop and leading to an improvement in crop yield. However, there are some agronomic issues that could occur from grazing over winter cover crops, such as creating issues with soil compaction and leaching of N deposited in urine in adverse weather conditions.

Nevertheless, such risks may be mitigated against by having a ‘back-up’ field nearby, ready to move the livestock into if ground conditions worsen. If livestock are not already present on the farm, then you can consider working with graziers or neighbouring farmers who could supply the stock, infrastructure, and expertise.

Forming a good relationship with the grazier is key to ensuring both parties benefit from the arrangement. This way you can also communicate easily and honestly about the removal date, bad weather strategy, the residual crop target, and the species mixture.

Please refer to the selection section of the website for information on grazing friendly species.

Below ground

Many of the organisms that make up the soil food web, from micro to macro fauna, carry out vital below-ground functions, including decomposition of SOM and transformation of nutrients into plant available forms. Cover crops may provide a bridge for organisms such as mycorrhizal fungi, providing living plant roots and sugary exudates that serve as their habitat and food, and can support wider soil microbial communities and increase overall microbial biomass. Macro soil fauna, particularly earthworms, mix soils and form channels that assist with water infiltration and crop rooting. There is some evidence to indicate that cover crops can also increase      populations of these species, especially earthworms, though these effects may also depend on other factors (e.g. the farms approaches to tillage operations).

Some ‘biofumigant’ cover crop species can even be used to target below ground pests and diseases, typically using the chemicals released by the cover crop post-termination. Certain brassicas have been extensively researched to this end to control nematodes such as potato cyst nematodes (PCN), though careful consideration needs to be given to termination times and residue incorporation for optimum performance.

A good number of earthworms (i.e., >8/pit = ‘active’ population for arable soils) are beneficial for soil function. You want a balanced community structure of earthworm species and ages, otherwise some earthworm-mediated soil functions could be compromised.