I’m getting high tech on my allotment. Well, to be more truthful, I’ve been using low tech means to achieve what is made possible on a larger-scale by ‘precision farming’.
This autumn, instead of digging the whole allotment I’ve not tilled it at all in some places, and in others I’ve dug the small areas where I’ve detected significant resistance to the penetration of a fork. In the intermediate areas I’ve eased the soil but not turned it over. This is almost real-time detection of soil strength determining the extent of cultivation required. I’ve then spread barley grains over the soil surface and covered them with around 5-8 cm of nicely rotted and very crumbly compost.
This is my first attempt at cover cropping and I hope to destroy the barley in December with glyphosate. The intention is that when I direct sow in the spring I’ll have the perfect seedbed for small seeded species. They should establish quickly because the surface layer will have been conditioned by the compost and the layers beneath will have been conditioned by the barley roots rather than slumping under the pressure of winter rainfall.
I realise that this is not original thinking and it mimics much of what a few farmers are now adopting. There’s little doubt that cover crops are now ‘in’ and they may have true benefits for many farmers. It seemed very different only a few years ago when NIAB TAG started research on cover crops at Morley (funded by The Morley Agricultural Foundation and the J C Mann Trust). At that time there was widespread suspicion of cover crops but this research has now proven to be a great asset. It takes many years to generate meaningful results and so it is a significant benefit to be ‘ahead of the curve’.
The results so far suggest that cover crops can just about financially justify themselves in terms of the increased value of the following crops that are receiving the recommended dose of applied nitrogen. The pay back from break crops increases when sub-optimal doses of nitrogen are applied to following crops. In addition, water infiltration rates into the soil have increased resulting in a significantly lower risk of surface ponding and run-off. This means a lower erosion risk and perhaps an opportunity to cultivate earlier in the spring. It’s still early days and, like many other soil conditioning approaches, it is possible that the benefits will increase over time.
Cover cropping is a large subject to research. There are lots of factors to take into account, particularly time of sowing, method of sowing and choice of species. The work at Morley suggests that legume-based cover crops are more beneficial to following crops than those based on brassica species such as mustard or fodder radish. There are two possible downsides to these types of cover crops; firstly the margins are slim and the seed costs are not cheap and secondly they may carry disease to related crop species.
It’s for these reasons that some farmers are choosing oats. Oats from the barn are cheap and do not carry over root disease in cereals, except for a relatively rare and localised form of Take-all. I chose barley because I don’t grow cereals on the allotment (!), it was too late in the year to sow a more exotic form of cover crop and I pinched the barley from a trailer at NIAB (white collar crime?).
As with any new approach, claims of its benefits can be exaggerated. There’s little doubt that cover crops can reduce nitrate losses in the winter. However, does this mean that less nitrogen needs to be applied to the following crop? This seems a logical conclusion, but in fact it is not true. A three-site study in Northern France concludes that whilst cover crops have consistently reduced nitrate leaching and increased nitrogen storage in the soil organic matter they have had, even after their adoption over at least a thirteen year period, no impact on the efficiency of bag nitrogen applied to crops. The same also holds true at Morley, over a shorter term of adoption, where the optimum dose of bag nitrogen for crops is the same in rotations adopting or not adopting cover crops.
Once again this proves why we should do field trials rather than get carried away with theories. It certainly helps to knock on the head the balance sheet approach to nitrogen nutrition adopted by some soil scientists. This method, which is also logically based on the amount of nitrogen the crop is likely to remove less the amount at the start of the season in soil mineral nitrogen and in the crop, is far less reliable than some considerably simpler approaches to predicting optimum nitrogen doses.