Launch of the industry Greenhouse Gas Action Plan on 4th April is a reminder of an issue that won’t go away but will just keep affecting us more and more. Agriculture accounts for some 8% of UK GHG emission mostly as methane and nitrous oxide. Methane comes mainly from manures and ruminant flatulence, less said the better. Nitrous oxide emission is related to amounts of nitrate-N in the soil, from whatever source, so has a clear link to fertiliser and manure use. The Action Plan has a lot to say about nitrous oxide and how the industry plans to minimize emission. Trouble is nitrous oxide forms during the breakdown of organic matter to nitrate and, especially, when nitrate denitrifies to nitrogen gas in water-logged or compacted soils. So, if we want nitrogen in the soil to be available for uptake by crops, we can’t avoid losing some as nitrous oxide. But, as the Action Plan shows, there are things we can do to keep emission to a minimum – even better; these are the same things that will help to get best return from the nitrogen used. Much of it is common sense and needn’t add to costs.
The real need is to give management of nutrients, especially nitrogen, the attention it deserves. In round terms, use of nitrogen doubles crop yield and a product that does that deserves respect. We need to take care in getting decisions on nitrogen use right, make sure spreading equipment is fit for purpose, properly set up and operated and any deficiencies in soil pH, soil structure and other nutrients are corrected. As ever, the nutrient contribution of organic manures must be taken into account. Doing these things needn’t cost a fortune but it will require some management time and a few key tools like the Tried & Tested nutrient management plan and the Fertiliser Manual. It’s very unlikely that any time spent on nutrient management will be wasted and very likely that it will bring a significant return.
Talking of other nutrients, sulphur emission to the air throughout the UK is still falling, one of the great environmental success stories, and this means more must be applied in fertilisers. Sugar beet is the latest crop for which sulphur is now recommended and the BBRO are suggesting that ammonium sulphate at 150 kg/ha can be beneficial on sandy and sandy loam soils. Sulphur use should be routine for oilseed rape though survey results show some 30-40% of the crop still does not receive any. Data for grass is worse; sulphur is applied to less than 15% of silage area even though this is the most responsive crop. I’ve come across fields that were topped-up with nitrogen because they were yellow. No effect – the problem was sulphur deficiency. As with nitrogen, a bit of time spent thinking about sulphur requirement and use will not be wasted.
Ian has over 30 years experience in fertilizer use and crop nutrition. He now runs his own consultancy, Ecopt, involved in all aspects of nutrient management, including provision of the FACTS technical information service and he is also a member of the steering groups for revision of RB209 in 1999 and the Fertiliser Manual from 2007.
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