CROP GROWTH AND WATER QUALITY RESULTING FROM THE INJECTION OF SEWAGE SLUDGE
Report No FR0113
C J Atkinson, Dept Engineering for Agriculture, Silsoe College
To assess the environmental, agronomic and operational implications of injecting sewage sludge into arable land with particular respect to nitrate and volatile fatty acid (VFA) emissions, and crop response.
Injecting sewage sludge prevents volatilisation of ammonia. Whilst this may increase arable crop yields compared with surface applications, greater amounts of nitrate may be produced and leached when sludge is applied to bare soil over the autumn-spring period. It is important that the mechanisms are understood and appropriate management practices are identified to minimise problems since there is increasing concern that sludge applications to land may be curtailed at certain times of the year to avoid nitrate emissions due to Nitrate Sensitive Areas or an impending EC Directive.
This report summarises the practical work carried out over the first two years of a three year studentship at Silsoe College funded by WRc. A full and final report will be prepared for March 1991.
The main effort has focused on large field trials on contrasting soil types on which matched applications of sludge have been applied either to the soil surface or by soil injection at various times over the September to April period, followed by cropping with winter or spring wheat. Soil cores have been taken to determine the distribution of nitrate and to identify the combination of operational, climatic and cropping factors which give rise to, or minimise nitrate emissions. The winter of 1987/88 was very wet, the subsequent two winters have been drier and mild emphasising the importance of repeating such trials over several years to avoid extreme climatic effects. The laboratory and field studies assessing the production and effects of VFAs following the injection of untreated sludge have revealed significant reductions in the germination of sugar beet. The operational significance of these findings needs to be assessed.
Copies of the Report are available from FWR, price £15.00 less 20% to FWR Members