FWAG South East Projects

Assessing Cover Crop Benefits to Soil Structure

In collaboration with South East Water and Kings Seeds, FWAG South East have been working with three farms to monitor the efficiency of cover crops in capturing nitrate in the soil. Three cover crop mixes will be compared to stubble and the benefits to soil structure and beneficial invertebrates will be evaluated.

Nitrate is a highly soluble compound that will leach through the soil into groundwater sources. Water companies have noted an increasing trend in nitrate levels in extracted groundwater, subsequently increasing the treatment costs to produce safe drinking water. Agriculture has been identified as a key source of excess nitrogen in groundwater, particularly during winter when high rainfall and bare soil increases nitrogen leaching.

Field experiments

Soil composition (nutrients and water)

Spring and autumn soil samples allowed us to compare differences in soil nutrients (nitrogen, phosphor, potassium and magnesium, pH and organic matter) as the cover crops grow.

Every two weeks, porous pots were used to obtain deep soil-water samples to identify the volume of nitrate leaching through the soil. This analysis is completed in the cover crop mixtures, bare stubble, Miscanthus, herbal ley on clay soil, herbal ley on chalk soil, woodland and permanent pasture to compare nitrogen leaching in under different systems.  For the 2022/23 experiment an area of strip till was also investigated for its nitrate leaching.  

Plant nutrient content

Spring nutrient analysis from a metre square of plant biomass from each plot will identify the proportion of nitrogen stored by the plant and potential benefit to following crop once the biomass has been incorporated.

Soil structure and Health

New to 2022/2023 a penetrometer was used to evaluate the soil structure and a moisture meter was used to collect data such a soil moisture and soil temperature when collecting water samples. Soil bacteria levels were also collected from the soil samples. 

A visual evaluation of soil structure (VESS) was completed in spring and autumn. 

Invertebrates

To understand which invertebrates are using the cover crops, pitfall traps captured insects for one week in September, October and November. Insects were identified to functional groups: predators of pests, pests, decomposers and other.

Slugs, which are crop pests, can thrive on the abundance of green material. Slug traps were set up and slugs were in autumn and spring to see if which cover crop mixture increased slug numbers.

Results

The project has consistently shown that cover crops absorb higher nitrogen levels, reduce nitrate in ground water, have better soil structure and can support a range of beneficial invertebrates, than compared to stubble.

We have also hosted workshops to inform farmers and agronomists about this work.

View project pictures below or to learn more visit the South East Water project page here.

FWAG South East LLP
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