Resilience – run for cover

28 Nov 2012

The yield plateau project which I referred to last week has started a flurry of emails. I received one from a farmer who has mapped out the average yields of the individual HGCA Recommended List winter wheat trials carried out over the last ten years. This shows the large variation in the average trial yields achieved in recent years compared to earlier years that experienced more benign weather conditions.

There may be a number of explanations for this; for example a change in trial sites. However, it could also indicate that winter wheat has insufficient resilience to withstand the weather shocks of recent seasons. For instance, the feature of 2011 was the prolonged drought from the end of February to the end of May, and the feature of 2012 was lack of summer sunshine and waterlogging in May and June.

The question this poses is whether we can increase the resilience of our crops in a future that seems to promise more regularly occurring weather shocks. Much is bound up in the physiology of the crop. I’ve written before about breeders’ attempts to ensure that a higher proportion of solar radiation is transferred into crop growth. This may help if we have years with such low levels of sunshine as in 2012.

However, droughts and waterlogging suggest we also have to think of trying to increase the resilience of the soil to provide the best conditions possible for crop growth. In addition, improving the ease with which good quality seedbeds are prepared is particularly relevant in years where more spring crops have to be grown because of a wet autumn. So, much of the resilience we seek in yields will have to come from making soils more resilient.

The glib response from some pressure groups and governments is to increase the organic matter of the soil. This would make soils more workable in a wider range conditions and increase water holding capacity. Well I agree, but the challenge is how do we do it? There’s not the necessary amount of organic manures and amendments available to increase the organic matter of all our arable land.

I remember that there was a suggestion a few years ago that to receive the single payment arable farmers would have to grow short-term leys in their rotations in order to increase organic matter levels. This soon got dropped when it was realised that any additional organic matter resulting from a short-term ley was soon lost when the land was returned to arable cropping.

An earlier blog did mention the value of the regular return of crop residues to the soil. This increases soil fungal biomass which provides some of the advantages of higher organic levels; for instance, soil fungal biomass increases the stability of soil aggregates. This means that seedbeds are easier to prepare and that they’re far less vulnerable to capping. However, to maintain soil fungal biomass it needs an annual return of crop residues or organic material.

An approach to further increasing soil fungal biomass activity is to grow cover crops, particularly prior to spring crops. I realise that there is a lot of hassle with this but the potential rewards of doing so are likely to be greater if the weather is going to become more variable.

In my opinion, one of the most valuable results of an HGCA project carried out by The Arable Group and Rothamsted Research (HGCA Project Report No 414) a few years ago never got any real publicity. It measured the value of growing mustard in the fallow year of a wheat cropping sequence (I don’t want to call it a rotation for fear of upsetting someone). This showed that after four years (and so after two mustard crops rather than bare fallow) the wheat yield was increased by 1 t/ha and both soil fungal biomass and soil water holding capacity were higher than when no mustard crop was grown.

Similarly, NIAB National Agronomy Centre’s New Farming Systems Project at Morley (funded by The Morley Agricultural Foundation and the JC Mann Trust) is beginning to show the accumulated value of cover crops sown in the autumn before establishing spring crops. The results show that legume-based cover crops are of particular promise. Hence, the evidence is building that if we want ‘living’ and more resilient soils in the absence of regular applications of organic manures, then we have to have the right plants growing in them for the maximum time possible.