Successive annual applications of organic manures for cut grass: short-term observations on utilization of manure nitrogen

The recovery of nitrogen (N) from, and the fertilizer-N value of, low dry-matter (DM) cattle slurry and farm yard manure (FYM), applied annually to perennial ryegrass swards grown at two sites, on sandy loam and shallow calcareous silty clay loam soils, were studied over a 4-year period. Slurry or FYM, applied at target rates of either 150 kg N ha(-1) or 300 kg N ha(-1) in either October, February or May/June, in combination with 150 kg N ha(-1) inorganic fertilizer-N (applied as split dressings before the first and second grass cut), were compared with a set of inorganic fertilizer-N response treatments. DM yield, N offtake, apparent manure-N recovery (in herbage) and manure-N efficiency (compared with inorganic fertilizer-N) were determined at two silage cuts each summer. Soil mineral nitrogen (SMN) measurements in autumn and spring were used to assess potential N leaching loss over winter and to quantify available N residues in the soil in spring. Apparent manure-N recovery and manure-N efficiency were usually greater from slurry applications in February than from those in October, but the timing of the application of FYM had a much smaller effect, compared with the timings of the application of slurry, on the utilization of N from manure by grass. Spring assessment of SMN was useful in quantifying available N residues from October slurry applications. Manure-N recovery for all application timings was, on average, higher from the sandy loam than the shallow calcareous clay loam. The application of slurry to grass in early spring, at a rate of 150 kg total N ha(-1), with the addition of a supplementary 50 kg inorganic fertilizer-N ha(-1), was the most suitable strategy for utilizing slurry-N effectively and for supplying the N requirement for first-cut silage.