24 Jul 2013

The temperature outside is 32°C.  What a contrast to last year.  The climate scientists now say that we will have to get used to variations in the weather that are accentuated by the increased carbon dioxide concentrations in the atmosphere.   These extremes have a huge impact on those businesses that rely on the weather, be it ice cream manufacturers, seaside hotels or farming.  There is a double whammy for some branches of agriculture because both demand and supply are influenced by the weather.  For instance, demand for salads is higher this summer than last but the market for summer cabbage, cauliflowers and calabrese has collapsed.

There is much talk about what arable farmers should do in order to minimise the impact of such extreme weather events on their businesses.  The word ‘resilience’ is used frequently and there are at least three technical issues.

November 2012 floodsFirstly, the cropping system should not be too dependent on one specific and limited weather ‘window’.  There are lots of examples of this but perhaps one has been particularly obvious over the last few years.  It is now essential for many farmers to spray the pre- or early post-emergence winter wheat herbicides for the control of black-grass onto a moist seedbed.  When this does not happen, the levels of control can be very low.   This can be disastrous in terms of yield where there is the potential for a high number of black-grass plants to establish.  A more resilient system would not have the potential for high numbers of black-grass.  This is easier said than done but it is the concept behind the NIAB TAG “Low Seedbank Farming” philosophy.

Secondly, the level of equipment and labour available should be sufficient to exploit fully the appropriate weather windows when they do occur.  I realise that this has to be balanced against costs but the NIAB TAG co-ordinated and Defra/HGCA funded ‘yield plateau’ study contains data that show that those farmers achieving the highest yields and financial margins have higher than average labour and machinery costs per ha.

Finally, cultivations and soil management have to be tip-top.  This includes maintaining effective drainage systems, ensuring that water can move to the drains without major impediment, maximising the ability of the soil to store water and enabling roots of a well established crop to extract the maximum amount of soil moisture.  Everyone knows that this is a huge subject and it is increasingly the topic under discussion with farmers and their advisers.

One part of the soil management issue is water infiltration rate.   Low infiltration rates mean the reduced ability of the soil to ‘take in’ water, which can be critically important when trying to store in the soil the maximum amount of limited rainfall in a dry summer.  Low infiltration rates also result in a higher likelihood of surface ponding, run-off and erosion.

Increasing soil organic matter is a way of increasing infiltration rates.   However, increasing soil organic matter levels is not easy due to the limited amounts of organic materials (soil amendments) available.   I suspect that incorporating rather than removing straw or other crop residues will also increase infiltration rates due to the resulting increased levels of soil fungal biomass.  I have written before about soil fungal biomass being a part-surrogate for soil organic matter.  The problem is that increased levels of soil fungal biomass from the incorporation of a soil amendment are typically only short lived, lasting up to 18 months.   Hence, there needs to be annual incorporation of residues to maintain levels.   

For several years The Morley Agricultural Foundation has been funding a series of experiments investigating resilience of cropping systems.   It has to be commended on its foresight.  One experiment is investigating how long the positive impacts of applying different soil amendments persist.  A surprising result was that only paper crumble appreciably increased infiltration rates in the second cropping year after application.  Possibly, this suggests that the initial impact of a single application of a soil amendment on infiltration rate is in part due to increasing soil fungal biomass levels.   A proportion of the paper crumble maintained its integrity into the second year which may have continued to help to keep the soil ‘open’ as well as to continue to be a food source for the soil fungal biomass.   This is limited data but if it is repeated then we will have to start to re-think how best to use manures to increase the resilience of cropping systems.