Keywords: Grassland systems, Nutrient losses, Animal manure, Emission reduction, Mineral balance.
In Western European countries much attention is currently paid to the negative consequences of nutrient losses from the agricultural production process to the environment. From animal husbandry the emission of nitrogen and minerals mainly occurs via urine and faeces. Agriculture plays an important role concerning the emission of ammonia. Ninety percent of the NH3 emission in the Netherlands is caused by animal manure. Other nitrogen (N) losses occur by leaching, surface runoff and denitrification.
On intensive dairy farms in the Netherlands at present only about 14% of the N and potassium (K) input and 33% of the phosphorus (P) input is recovered in milk and meat, mainly because of poor utilisation of nutrients in the manure. Recently the government of the Netherlands has set a number of targets to reduce N and P losses within the next 10 years. In order to develop a strategy to diminish the losses it is relevant to have figures about the size of these losses at each step of current production processes and about the possibilities for reducing these losses.
In this paper the extent of mineral losses from grassland systems by volatilisation, leaching, runoff and denitrification, as well as the N flow via immobilisation and mineralisation are discussed. Furthermore measures are described to reduce the losses of ammonia volatilisation from stall and slurry storage, slurry application and by a better supplementation of the ration at grazing. Leaching and runoff can decrease substantially through better balancing of nutrients from animal manure and fertiliser and by application of all nutrients during the growing season. To get the best results, all the different steps to reduce losses have to be geared to each other, so that the whole production process can be optimised.
Experiments on farm scale are described. On one farm applying a set of measures to reduce losses resulted in a reduction of ammonia volatilisation of more than 50% within a couple of years. The surplus of N, P and K on a mineral balance can be reduced considerably by a better management of feeding and manuring.
H Korevaar, Agricultural Research Department DLO, PO Box 59, 6700 AB Wageningen, Netherlands.
D J den Boer, Netherlands Fertilizer Institute (NMI), seconded to Research Station for Cattle, Sheep and Horse Husbandry PR, Runderweg 6, 8219 PK Lelystad, Netherlands.
34 pages, 6 figures, 11 tables, 52 references.