Uncovering cover crops

Cover crops are very much a hot topic at the moment.  They seem to have so much to offer – improved soil structure and organic matter, retained nutrients, erosion limitation, and even blackgrass control.  But not everyone is convinced of their merits.  It’s all very well farmers with light land in the south extolling their virtues, but what of the rest of us?  And in these challenging economic times, do they pay?

We don’t have the answer to all these questions, but we are learning a lot about the potential of cover crops on cold wet Midlands clays through a rigorously designed experiment that has been running for the past year.  The research is part of our contribution to Defra’s Sustainable Intensification research Platform (SIP).  We are still analysing the data, but I can share some interim findings.

We looked at three different mixtures, oats and Phacelia; oats, Phacelia and radishes (oil and tillage); and oats, Phacelia, radishes and legumes (vetch and clovers).  We also had a bare stubble control plot in each of the three fields in which the experiment was replicated.  Our Soil Scientist, Dr Felicity Crotty has been gathering data on soil physical, chemical and biological properties, while our Farm Manager, Phil Jarvis is gathering yield and economic data.

Soil Scientist, Dr Felicity Crotty

Felicity quantified the effect of drilling the cover crops on soil structure in comparison to the bare stubble control which had not been driven over by machinery, and by the end of the winter, the soil structure had visibly improved and compaction was reduced in all the cover crop treatments while the bare stubble control remained unchanged.  The oats, Phacelia and radish mixtures had slightly greater plant cover, but importantly, significantly lower biomass of weeds such as blackgrass.  There were some significant differences between cover crop mixtures in soil biology, specifically surface dwelling earthworms and millipedes, which may have implications for organic matter breakdown and incorporation into the soil.  The radish based mixtures were also associated with the highest yield in the following spring oats crop, and lowest weed biomass, compared to the stubble control plots.  Further analysis, especially of the economic data, will enable us to evaluate these mixtures more fully.

Our interim findings for the first year suggest that cover crops can reduce weed populations and enhance yield through improvements in soil function, but we now need to discover whether such benefits justify the cost incurred by establishing the cover crops in the first place.  Meanwhile, cover crops have been established in a new experiment this autumn, this time looking in more detail at the specific components of the mixtures so that we can understand better the role of each species. 

The spring oats following last year’s cover crops have now been replaced by wheat.  Next year we will assess the yields of that crop in relation to the different cover crop mixtures.  Our aim is to understand the implications of cover crops, not just in terms of immediate costs and benefits, but also as part of a rotation.