The effects of pig manure type and application timing and frequency on nitrate leaching from a seven-course arable rotation on a retentive alluvial soil

Management rules for integrating manure applications into arable crop rotations have generally been developed from short-term studies. The aim of this experiment was to test if they would apply to frequent applications across an entire crop rotation. The hypothesis was that by avoiding autumn manure applications and adjusting fertiliser inputs to account for manure N inputs, frequent manure applications could be made to a rotation without increasing nitrogen (N) leaching compared with a control that received inorganic fertiliser according to recommended rates. Four separate manure management strategies with varying manure types (pig slurry vs. pig farmyard manure), timing (autumn/winter vs. spring) and frequency (4-7 applications in 7 years) were superimposed on the rotation and compared with a treatment that received no manure. The rotation comprised cereals, potatoes, sugar beet and fallow and was undertaken on a retentive marine silt soil in Eastern England. The results demonstrated that by reducing fertiliser N inputs (by 14-54%, depending on manure type and application frequency) to account for manure N and by avoiding autumn applications of slurry, applications could be made as regularly as six years in seven without increasing N leaching, compared with an inorganically fertilised control. Yields were at least the same as the inorganically fertilised control from all manure treatments. This result contrasts with previous work which demonstrated less frequent manure applications were necessary on a sandy soil. Soil type is therefore an important consideration when developing guidelines. The message is generally positive: fertiliser savings, similar or better yields and no extra leaching can be achieved over a rotation by careful manure management.