Pant Farm

Winter monitoring of water quality in the Trothy river catchment in Monmouthshire has revealed spikes in river phosphate levels following a high rainfall incidence. This could be in part due to soil run off from bare maize stubbles in an area where increased areas of maize are being planted to supply biodigesters. Establishing a crop or cover after maize harvest is often not realistic because of autumn soil conditions and problems associated with late autumn sowing.

Following experience in Denmark where thousands of hectares of maize are now under-sown a new technique designed to protect maize stubbles from soil erosion and leaching over winter has been developed. The technique involves the under-sowing of a cover crop into maize, usually Italian or Perennial Rye Grass, at precisely the right time and stage of maize growth.

This technique could help growers comply with greening rules, meet the requirements of cross-compliance and  potentially cut the pollution of water courses with leached nitrogen, other minerals and silt. In addition, trials have shown the under-sown crop has the potential to produce up to three tonnes of dry matter per hectare. This can then be grazed or ploughed in as green manure, which will aid soil organic matter, structure and fertility. All this has also been achieved without significant impact on maize yields.

Harvesting the cover crop for silage the following spring may be challenging as the soil surface can be uneven following maize harvesting operations creating the risk of soil contamination. The field will also have significant quantities of maize stalks, unless these are flailed off immediately after harvest. Grazing with sheep or young cattle is probably most appropriate, and even in late harvesting seasons, Italian Ryegrass has produced 3 t/ha dry matter by the end of March at about 12 ME and 12% CP. This has the potential to produce >1,500 ewe grazing days or 300 heifer grazing days per hectare.

Project aims:

• To demonstrate the use of under-sown rye grass as a means to stabilise soil under maize stubbles over winter
• To provide knowledge on the optimum time of rye grass establishment following the planting of a maize crop
• To estimate the cost benefit of under-sown rye grass in terms of animal grazing output
• To examine any potential benefits in soil structure, organic matter and fertility resulting from the under-sown crop 

What will be done:

The target period for sowing grass seed into maize is from one week after the last herbicide is applied through to the stage when the crop is about knee-high in early July. Danish trials suggest that establishment can be greatly enhanced by drilling the seed and consolidating behind the drill rather than broadcasting grass seed or broadcasting and harrowing, both of which require rain to be effective. Drilling improves reliability of establishment and allows lower seed rates.

Italian Rye Grass provides the most vigorous option and has the potential to produce optimum biomass yield after the maize has been harvested. Being less vigorous, Perennial RG is potentially better suited to earlier sowing, and because of the higher number of seeds/kg it can be sown at very low seed rates.

Carrying out cultivations in growing maize crops with inter-row drilling equipment is a job for experienced operators. A specially modified drill has been developed by the Wye and Usk Foundation and the service will be provided by Field Options who will organise the  drilling and seed and coordinate the operation. The drill is set up for 6 row or 12 row drill format with standard row spacing of 75 cm (30 inch), but tolerances have been built in to the drill to allow under-sowing in crops sown with an 8 row drill. All maize drilled at 75 cm with GPS guidance should be suitable.

Possible monitoring of winter soil water run-off in terms of quality and quantity will also be examined from bare maize stubble compared with the under-sown site.