Manure management practices applied to a seven‐course rotation on a sandy soil: effects on nitrate leaching

This experiment tested whether it was possible to incorporate broiler litter ( BL ) or cattle farmyard manure ( FYM ) into a 7‐yr arable rotation on a sandy soil without causing an increase in nitrate‐nitrogen ( NO 3 ‐ N ) leaching. Four manure treatments (with adjusted fertilizer inputs), varying in frequency and timing of application, were imposed on the rotation and compared with a control that received inorganic fertilizer according to recommended rates. Over seven winters, the annual average NO 3 ‐ N leached from the inorganic fertilizer treatment (control) was 39 kg/ha in 183 mm drainage. Total manure N loadings over the period of the experiment ranged between 557 and 1719 kg/ha (80–246 kg/ha/yr) for the four treatments. Three of the four manure treatments significantly increased NO 3 ‐ N leaching over the rotation ( P  <   0.001). Annual applications of FYM (1719 kg/ha manure N or 246 kg/ha/yr) increased NO 3 ‐ N leaching by 39%. We hypothesize that this was due to increased mineralization of the organic N accumulating from repeated FYM applications. BL applied each year (1526 kg/ha manure N or 218 kg N/ha/yr) increased NO 3 ‐ N leaching by 52% above the control; BL applied 5 of 7 yr (972 kg/ha manure N or 139 kg N/ha/yr on average) and including inadvisable autumn applications increased leaching by 50%. BL applied in late winter or early spring every 2–3 yr (557 kg/ha manure N or 80 kg N/ha/yr on average) resulted in NO 3 ‐ N leaching similar to the control. This suggests that to avoid additional NO 3 ‐ N leaching from manure use in an arable rotation, manure should not be applied every year and autumn applications should be avoided; there are real challenges where manure is used on an annual basis.