Irrigation and lava meal use reduce ammonia emission and improve N utilization when solid cattle manure is applied to grassland

Considerable losses of nitrogen (N) may occur during and after surface-application of solid cattle manure to grassland. These losses are due mainly to the emission of ammonia (NH3) and represent a threat to the environment. Consequently, N fertilizer value of the manure is reduced. Therefore, adjusted manure application strategies were evaluated in three field experiments focusing on NH3 emission and herbage N recovery. Fresh, composted and anaerobically stored solid cattle manures were surface-applied to grassland at a rate of 400 kg N ha-1 with or without irrigation and/or lava meal addition. NH3 emissions were estimated by means of diffusion samplers installed 20 cm above the soil surface for a period of 3–4 days. Irrigation (5 mm) immediately after applying fresh manure reduced (P <0.05) NH3 emission by 30%, whereas it was not effective in the case of composted manure. Irrigation (5 and 10 mm) following application of anaerobically stored manure reduced (P <0.001) NH3 emission by 65 and 92%, respectively. Lava meal addition before application at a rate of 80 g kg-1 manure resulted in an emission reduction (P <0.05) of 46%. The combined use of lava meal and 10 mm irrigation led to a reduction of 97% while apparent recovery of the manure N in herbage increased (P <0.05) from 18 (untreated control) to 26% over three harvests in 5 months’ time. Effects of irrigation were restricted to the first grass harvest only, whereas the positive effects of lava meal were still present in the second harvest. It is concluded that both the use of lava meal as manure additive and irrigation immediately after manure application can reduce NH3 emission and improve herbage N uptake