When any new technique is employed, its initial benchmark for success is a measure of the financial return it provides over the technique it replaces or enhances. In that respect, catch and cover crops have had a rocky start in their introduction to UK farms.
This is largely because the financial positives – or negatives – from a cover crop in the initial stages of introduction are marginal with the potential for a negative financial impact often overriding the positive.
But measuring the success or value of a catch or cover crop based purely on its yield impact in a single fails to recognise the significant improvements in soil structure, biology, nutrient flow and water management that happens over a longer time.
As details of the Sustainable Farming Initiative become clearer, there is little doubt that cover crops, reduced cultivation practices, soil assessments and improvement will be central to accessing government support over the coming decade.
Due to launch next year, the Sustainable Farming Initiative is part of the government’s forthcoming Environmental Land Management scheme (ELMs). It will be introduced as the basic payment is phased out over the next few years.
Increasingly research is demonstrating the importance of below ground biomass in the building of soil organic matter (SOM) with figures recording over 40% of root matter being retained as SOM while top growth contributes only 8% to SOM.
Cash crops must not be forgotten in the process of building SOM but catch and cover crops play a vital role in filling the gaps in rotational cropping, in particular being present during the August to November period when UK soils are traditionally bare from post-harvest cultivation.
The value of catch and cover crops is immense when sown earlier during this period to intercept those longer days of sunlight energy and recharge the soils biological battery. For this reason, growers should choose a cover that works for their situation.
Choice of cover is crucial to performance, addressing issues in individual fields and matching the farm’s management approach out of the cover period – be that grazing, rolling, spraying and direct drilling or cultivation.
Cover crops can be used to improve carbon sequestration. Nitrogen ratios within the soil can impact the its ability to ‘digest’ high lignin residue like wheat straw. And they also can be used to slow the ‘burn rate’ of SOM in lighter soil fractions.
The focus is knowing what the state the soil is in and what it needs. Cover crops can add significant diversity into rotations and are an ideal opportunity to get legumes into the cropping cycles – and reduce reliance on applied artificial nitrogen.
The following crop must also be considered as there is significant risk of yield reduction where oats or rye form a high proportion of the cover crop mix prior to spring barley or wheat. Where cereals dominate the rotation, utilising oats as the cover adds little in diversification terms.
Consistently successful cover crops are made up of multiple species. The species mix should be optimised to the targeted impact required while bringing diversity, nutrient fixation, storage and release.
Ease of use like seed flow characteristics through air seeders and overall rates of use to fit with smaller air seeder hoppers is a further consideration along with reliability of species with the UK climate.
At Hutchinsons, our seed mixtures have been optimised for reliability and performance. Typically, they contain eight species with crop volunteers making it a nine species population.
Ratios in the mixtures are adjusted to optimise the area of performance, be that soil structural impact, nutrient release and fixation, water pumping or surface protection.
Transition from one cultivation system to another takes time – both for growers to gain confidence and for soil to improve. Now is an ideal time to make the change while support payments remain to help counter the risks and tweaks required for any system as it establishes itself on farm.
Dick Neale is technical manager for agronomy company Hutchinsons.