Is it time to start feeding cover and companion crops?

“It is too easy to think that because cover and companion crops contain a high proportion of nitrogen-fixing legumes, that they are self-sufficient from a nutrition perspective. That is simply not the case.”

With legumes becoming an increasingly important part of both arable rotations and forage-based systems in the form of clover, growers should not forget that they have nutritional needs like any other crop, and if their benefit is to be maximised.

Many people are focused on how such crops can generate their own Nitrogen, for yield or for the subsequent cropping, but it is vital that they have sufficient access to other nutrients to maximise their genetic potential and this can be overlooked, says ICL Growing Solutions agronomist Scott Garnett.

“It is too easy to think that because cover and companion crops contain a high proportion of nitrogen-fixing legumes, that they are self-sufficient from a nutrition perspective. That is simply not the case.

“Legumes are still crops and in order to maximise their potential, and their ability to fix Nitrogen, they require proper nutrition including adequate supplies of key nutrients like Phosphate, Potash, Magnesium and, especially Sulphur.

“Without adequate sulphur, the plant is simply unable to fix sufficient Nitrogen to maximise yield, produce proteins where necessary and its ability to contribute to subsequent crops will be significantly reduced.”

Is new thinking required?

Encouraged by SFI and the challenge of reducing nitrogen use in crops adoption of cover and companion crops is growing rapidly, but their management is a relatively new area for industry advisors, he says.

“Under the latest SFI, NUM2 pays £102/ha for improving grassland by growing legumes from spring until early autumn, whilst growers will receive £151/ha under LIG1 and LIG2 to include flowering grasses and wildflowers in grass leys during the summer months.

“There are further benefits to be had from using companion crops in arable rotations, with one of the biggest questions being what can they deliver in terms of kg of N/ha and to what extent can they reduce the dependency on bagged Nitrogen.

“It’s easier perhaps easier to justify adding nutrition in a livestock situation to help increase clover for example, improving nutritional management can translate directly into greater milk or meat production. Similarly, if growing commercial crops likes peas and beans where yield is important”. 

“Trials in peas and beans with the Pea Growers Research Organisation (PGRO) over many years using Polysulphate (48% SO₃, 14% K₂O, 17% CaO and 6% MgO) to provide a nutritional boost have shown significant gains in yield of harvested crop, often in the region of 10 – 15%.

“We already know adding a product like Polysulphate to legumes works and directly translates into yield and quality benefits.”

© ICL Growing Solutions UK

Sulphur supply critical

Key nutrients required by both cover crops in livestock systems and companion crops in arable rotations are Zinc, Manganese, Cobalt and Molybdenum as well as Phosphate, Potassium and Sulphate, Scott Garnett says.

“Sulphur is particularly important, not just to drive the highest levels of nitrogen utilisation, but also to improve protein content which is important in both forage and cereal crops.

“Polysulphate, either in fertiliser blends or by itself, has proven particularly beneficial in both organic and conventional farming systems by delivering high levels of usable sulphate, with its prolonged release nature reducing many of the potential environmental issues associated with other sulphur sources.

“As multi-nutrient fertilisers, Polysulphate-based products are perfect for providing macro nutrition and are also able to be a carrier for micro nutrients.” 

Maximising potential

Given the central importance of legumes to future UK strategy, ICL believes it is now time to look at how growers can maximise their benefit.

“It could prove beneficial for growers to consider re-investing some of the monies received from SFI into improving the nutrition and management of cover and companion crops,” Scott Garnett points out.

“With many sources suggesting a well-managed cover crop can fix 80 – 100kg N/ha and companies exploring the possibilities of increasing their genetic potential further, it is certainly a topic that merits further debate.”