Biosolids, Yield, Organic amendments in SOil. research to mitigate LeachIng and Denitrification: BYOSOLID

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Work at Rothamsted strongly suggests that by adding organic matter to soil, crop yields can be improved over and above any response to the nutrients that the amendments contain. The mechanism appears to be that soil organisms feeding off the amendments improve soil structure and thus allow plants to establish and find water and nutrients more easily. Crops grown in amended soils do especially well in years when crop yields are impacted by dry springs or wet winters. Work is underway at Rothamsted to better understand the mechanisms behind these observations. This project seeks to extend this knowledge to the duration of the benefit: how many years after an amendment has been added can the benefits to yield still be seen and how great might these be? There are many materials that are or could be added to soil and which ought to increase yields in this way: manure, compost, anaerobic digestate (AD), biosolids. Recycling these materials on land makes sense since they are all derived from agriculture in one way or another. However, there are regulations associated with their use. EU regulations restrict applications of materials containing N and P in Nitrate Vulnerable Zones and if a material is defined as a 'waste' (and some of these are) then the licensing issue becomes one of disposal rather than recycling. Current projects at Rothamsted have as their aims to produce guidelines to farmers on the use of organic amendments to improve crop yields. Because of the risk of environmental pollution from these materials there is a risk that regulatory agencies might refuse to permit the use of organic amendments or restrict their use still more than at present. This project aims to quantify not only the risk of N emissions from the direct application of amendments but also the residual release in the years subsequent to application. The project will examine emissions of N in a number of experiments currently receiving amendments, experiments that will cease to receive amendments during the course of the project and experiments which received amendments historically but which ceased during the last 10 to 15 years. In all cases, we know we can find the plots and have records of land management since amendment. Thus we expect to be able to build up knowledge of the loss of nutrients from land that last received amendment between 0 and 15 years ago on a range of soil types for several different kinds of amendment. Gaps will be filled by interpolation using computer simulation models. Such a comprehensive study should help mitigate the risks of restrictions being placed on the recycling of organic materials to land or provide objective evidence in support of their beneficial use or proscribe the extent of any restriction. Fertiliser N is most economically applied at the Break-Even Ratio (BER) - where application of one more increment of fertiliser only just pays for one more increment in yield. Organic amendments at Rothamsted appear to change the response of crops to added N and hence the N at BER and the amount of yield expected. Benefits from amendments will be expressed in terms of the change in position of the BER relative to yield and fertiliser N applied and in terms of the cost of fertiliser and the value of product. APW has been in touch with Anglian Water about this project and with HGCA, both of whom could be major beneficiaries. PW has also talked to the composting industry about the potential results.