Objective dairy farming system ‘De Marke’

Table 2 Maximum levy-free see text for explanation nutrient sur- pluses in the Netherlands kgha, deposition and fixation by clover not included 2000 2002 2005 2008 1998 N Grassland 300 275 250 200 180 150 125 110 175 100 Arable land P 15 13 17 11 Grassland 9 15 13 Arable land 11 17 9 for farming systems were defined Table 2. These threshold values are temporary political com- promises between environmental demands and agricultural possibilities Dekker and van Leeuwen, 1998. Surpluses above the levels presented in Table 2 will be levied. However, uncertainty exists among dairy farmers on the impact of a reduced surplus of P through lower inputs of fertilizer or concen- trates on soil fertility and — as a consequence — on crop production. Moreover, reducing the P surplus may lead to high costs because it limits the application of slurry, which then has to be exported or additional land has to be bought. This legislation stimulates more efficient nutrient management as farmers try to avoid fines while maintaining production. These measures have resulted in reduction in the surpluses on commercial farms Aarts et al., 1999, but further reductions are necessary. One of the goals of agricultural research is to develop guidelines for farmers to design and im- prove their farms, taking into account their spe- cific circumstances such as soil type, and both short- and long-term objectives. In addition, the government needs information on the practical feasibility of measures aimed at reducing the envi- ronmental impact of dairy farming. This paper describes the results of farming systems research focusing on dairy farming on sandy soils and long-term objectives with respect to nutrient sur- pluses, and, hence on improving nutrient manage- ment.

2. Objective dairy farming system ‘De Marke’

A dairy farm can meet the environmental objec- tives of the government by extensification, i.e. by producing less milk per hectare Weissbach and Ernst, 1994. For a given milk quota at farm level more land will then be needed, which, especially in the sandy areas, is scarce and expensive. In the Netherlands land taken out of production is mainly used for nature development, recreation, housing, industry and extension of infrastructure. Extensification i.e. reducing milk production per unit area without area expansion leads to re- Surplus P mainly accumulates in the soil, in addition to some surface flow, but continued ac- cumulation will lead to saturation and leaching. Hence, the quality of the Dutch environment is threatened and one of the world’s most vital and scarce minerals is wasted Tisdale et al., 1985. Since the middle of the eighties the Dutch government is making efforts to reduce the nega- tive impact of farming on the environment by formulating norms for nutrient surpluses. For ni- trogen this implies that groundwater may contain only 50 mg nitrate per litre — on light sandy soils it is now often more than 200 mgl Boumans and van Drecht, 1995 — and that ammonia emission from faeces and urine should be limited to 30 of the average level in 1980, i.e. an annual loss of 30 kg NH 3 -Nha at most. Field data suggest a required P supply in excess of crop uptake of 10 – 30 kgha per year to maintain an optimal soil fertility level from an agricultural point of view. Based on average precipitation surplus and Dutch groundwater quality standards maximum of 0.40 mgl P-total, a loss of about 1 kg P 2 O 5 ha per year would be acceptable, compared to about 30 in the mid-eighties Oenema and van Dijk, 1994. Hence, to meet the standards for the year 2008 the P surplus has to be reduced by 72. To realize those norms, first the use of animal manure was restricted on the basis of P load. As a result animal manures were better distributed over the country, but surpluses of N and P de- creased by only 14 Brouwer et al., 1997 and, thus, remained unacceptably high. Subsequently in 1997 maximum permitted surpluses of N and P duced milk production and, hence, a strong de- crease in income. Moreover, it is doubtful whether the growing world population can be provided with enough high-quality food in the future with a reduction in the area of cultivated land and more extensive land use. In the coming decades doubling of food production is expected to be necessary. Hence, the project ‘De Marke’ aims at reducing environmental problems by fo- cusing on the question to what extent technologi- cal options to improve nutrient management on dairy farms offer opportunities to maintain milk production per hectare. Characteristic for the dairy farm is the combi- nation of plant and animal production. Animal manure and roughage form the links between the animal and the plant components. Nutrients not exported — in milk and animals — or lost, pass through a cycle: part of the nutrients from fodder is excreted by the animals in faeces and urine. This manure is being used in crop cultivation, its nutrients are taken up by the crop and then again consumed by the cattle. Nutrients exported in milk and animals and lost in the cycle are com- pensated for by the input of nutrients in fertilizers and purchased roughage and concentrates. Nutrient flows can be influenced by manage- ment, aiming at reducing losses. For instance, at most farms cattle take up much more nitrogen than is necessary physiologically. Hence, a reduc- tion in the nitrogen content in the ration will hardly affect milk production, but will lead to less nitrogen in the urine and, consequently, lower losses. It is important that, wherever possible, measures in the different parts of the cycle be mutually synergystic, and geared to the specific possibilities and limitations of the farm. Cost minimization is an important criterion. The objective of this project is to design, test and further develop a farming system that can serve as a starting point for the development of dairy farms on dry sandy soils with average milk production about 12 000 kgha. The farming system should meet the strict environmental norms derived from policy papers as indicated in Section 1. To avoid desiccation the use of ground- water should be limited. Hence, irrigation is ap- plied, but restrictively. Water stress may have negative effects on utilization of already applied fertilizers environmental considerations and may require purchase of larger quantities of fodder economic and environmental considerations. Manure production is restricted to the amount that can reasonably be applied at the farm.

3. Research methodology