Presentations 2016

Nitrogen surplus key factor in relation between farm practices and water quality

Agricultural Economics Research Institute (LEI)

https://www.youtube.com/watch?v=p2sjFYmCvwk&index=5&list=PLZC-5vj9_JAYC2i99zybgBpF-Iq1U3Tb4

The effects of the EU Nitrates Directive Action Programme are monitored in The Netherlands via standard programmes for groundwater and surface water, and a special programme known as the Dutch Minerals Policy Monitoring Programme (LMM) based on a national network for measuring the effects of the Manure Policy. LMM uses an effect monitoring approach to assess the contribution of nitrate from agriculture to receiving waters and the effects of changing agricultural practice on these losses. LMM monitors therefore both water quality and the farm management that might influence this quality. LMM data on water quality and farm management showed the importance of N-surplus on the soil as an indicator for water quality. Therefore within the LMM-programme there is a strong focus on farm management factors that effects N-surplus. For this a solid method is needed in order to assess comparable N-surpluses for different farm types and soils. This contribution describes the assessment of N-surplus based on a soil balance method. Furthermore it presents the relation between N-surplus and water quality and the relation with the Dutch policy on manure and the amount of N-fertilization for the period 1991-2013.The surplus on the farm gate balance is first calculated by determining the total annual input (for instance inorganic fertiliser, feedstuffs) and output (for instance animal products, crops and other plant products) of nutrients as registered in the farm records. Stock changes are taken into account when calculating this surplus. The calculated nitrogen surplus on the farm gate balance is then corrected to account for input and output items on the soil surface balance. Allowance is made for net mineralisation of organic substances in the soil, nitrogen fixation by leguminous plants, ammonia emission and atmospheric deposition. The phosphate surplus on the soil surface balance is equal to the surplus on the farm gate balance. A state of equilibrium is assumed when calculating nutrient surpluses on the soil surface balance, except for peat soils. On Dutch peat soils a net mineralisation occurs. For different farm types the method and data is useful to calculate the nutrient surplus on the soil balance. Comparisons can be made between farm types and within one type between regions. For dairy farms the soil surpluses for nitrogen and phosphate amount to 181 kg of N and 12 kg of P2O5 per hectare (Figure 1, phosphate is not shown). The nitrogen surplus has remained at the same level for the past few years, while the phosphate surplus is still decreasing as a result of the Usage Standard System. The soil surpluses for nitrogen and phosphate at arable farms amounted to 110 kg of N and 19 kg of P2O5 per hectare (Figure 1, phosphate is not shown). The nitrogen surplus has more or less stabilised since 2008, while the phosphate surplus continues to decrease. N-surpluses as well as nitrate concentrations differ between farm types and between regions (not shown). Dry-matter yields of grass are hardly changed despite a lower fertilization level, due to better farm management. Figure 1 Nitrogen applied (kg/ha) and Nitrogen surplus (kg/ha) for Dutch dairy and arable farms in the 1991-2013 period