Effects of short‐term nitrogen supply from livestock manures and cover crops on silage maize production and nitrate leaching

Resource use efficiency requires a correct appreciation of the nitrogen ( N ) fertilizer replacement value ( NFRV , percentage of total N applied) of manures. We assessed the NFRV s of the liquid fraction originating from separated pig slurry ( MC ), untreated pig slurry ( PS ), untreated cattle slurry ( CS ), the solid fraction from separated pig slurry ( SF ) and solid farmyard manure from cattle ( FYM ) in two consecutive years in silage maize grown on a sandy soil. Maize yields responded positively to each of these N sources applied at rates up to 150 kg of mineral fertilizer equivalents per ha per year (i.e. NFRV  × total N rate). The observed NFRV s, relative to calcium ammonium nitrate fertilizer, amounted to 78% for MC , 82% for PS , 79% for CS , 56% for SF and 34% for FYM when averaged over both years. NFRV s were positively related to the ammonium‐ N share in the total N content. Rye cover crop establishment after the harvest of maize reduced nitrate concentrations of the upper groundwater by, on average, 7.5 mg nitrate‐ N /L in the first year and 10.9 mg/L in the second year, relative to a bare soil. Regardless of the presence of a cover crop, nitrate concentrations responded positively to the applied rate of effective N (total N  ×  NFRV ) but less to postharvest residual soil mineral N .