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 (NO3-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 NO3-N leached from the inorganic fertilizer treatment (control) was 39kg/ha in 183mm drainage. Total manure N loadings over the period of the experiment ranged between 557 and 1719kg/ha (80-246kg/ha/yr) for the four treatments. Three of the four manure treatments significantly increased NO3-N leaching over the rotation (P<0.001). Annual applications of FYM (1719kg/ha manure N or 246kg/ha/yr) increased NO3-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 (1526kg/ha manure N or 218kg N/ha/yr) increased NO3-N leaching by 52% above the control; BL applied 5 of 7yr (972kg/ha manure N or 139kg N/ha/yr on average) and including inadvisable autumn applications increased leaching by 50%. BL applied in late winter or early spring every 2-3yr (557kg/ha manure N or 80kg N/ha/yr on average) resulted in NO3-N leaching similar to the control. This suggests that to avoid additional NO3-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.