1 Department of Agroecology - Soil Fertility, Department of Agroecology, Science and Technology, Aarhus University2 Department of Agroecology - Climate and Water, Department of Agroecology, Science and Technology, Aarhus University3 AEA, Didcot, UK4 ALTERRA, Wageningen5 University of Natural Resources and Life Sciences6 NEIKER, Derio7 Swedish Institute of Agricultural and Environmental Engineering, Uppsala8 Swedish Institute of Environmental Resources and Engineering, Uppsala9 Department of Agroecology - Soil Fertility, Department of Agroecology, Science and Technology, Aarhus University10 Department of Agroecology - Climate and Water, Department of Agroecology, Science and Technology, Aarhus University
Using the nitrogen (N) in organic manures more effectively reduces losses to the environment. A requirement to take allowance of the N conserved by reduced ammonia (NH3)-emission techniques would increase manure-N efficiency by up to 15%. Covering manure stores and land application of slurry by injection beneath the soil surface and by rapid incorporation of both slurries and solid manures into uncropped soil reduce NH3 emissions. Injection of cattle slurry also reduces N immobilization compared with application methods, which mix the slurry with soil and increases manure-N efficiency by ca 10–15%. In growing cereals, NH3 emissions can be reduced by band spreading within the canopy. Anaerobic digestion of slurry may also increase manure-N availability in the season of application by 10–20%, compared with undigested slurry. Slurry acidification may increase manure-N efficiency by 35–65% by reducing total NH3 losses by 70% compared with unacidified slurry stored without cover and not incorporated after spreading. To fully utilize the fertilizer value of manure-N, uptake over more than 1 year needs to be accounted for. This is particularly important for solid manures which provide less-available N in the season after application than slurries but release more N to crops in subsequent years. Using manure-N as a sole N source may limit overall manure-N efficiency. Applying manures at reduced rates over a larger crop area, using N fertilizer at times when crop recovery of manure-N may be limited, may give the greatest overall manure-N efficiency.