Catch Crops: How they can aid water quality in our rivers and lakes.

Catch crops are short-term, fast-growing crops sown between cropping seasons. They absorb excess nitrogen from the soil following the harvest of a cereal or oilseed crop and prevent nitrate leaching over the winter months.

The leafy crops help to protect the soil from exposure to heavy rainfall, also helping to prevent soil erosion, phosphorus run-off and sediment loss. They help to maintain soil biology, good for biodiversity and improve soil organic matter and suppress weeds. They are  regarded as being good for climate change as they help retain carbon in the soil. Unlike cash crops, they are not grown for sale, but to benefit the soil.

The experiment

During the National Ploughing Championships in September, scientist Aoife Egan conducted an experiment to illustrate the benefits of catch crops.

A perspex box was divided in half. Both sides contained free-draining sandy soil.

One-half was covered by a catch crop containing white clover, mustard, fodder and tillage radish, linseed, Phacelia and vetch. The crop was eight weeks old at the time of the experiment.

On the other side of the perspex box was bare soil with some stubble from the previous crop.

Equal amounts of red fluorescent dye were added to both sides of the box. This was to simulate nitrate application. Equal amounts of water was added to both sides of the box to simulate rainfall.

The runoff of water through the soil was collected in a drip tray. Our observations noted that more nitrate and water were retained where catch crops were grown, as opposed to that retained in just bare soil.

Results

Even though equal amounts of water were added to both sides of the box, less water was collected in the drip tray from the catch crop, compared to the bare soil, highlighting improved water-holding capacity caused by the living roots of the catch crop. This shows us the importance of using a catch crop to cover the soil between sowing the main crops, to reduce runoff of phosphorus, leaching of nitrates and sediment loss.

See video to watch the experiment underway:

Catch Crops Experiment Video Final.mp4