Trade-offs in soil fertility management on arable farms

Crop production and soil fertility management implies a multitude of decisions and activities on crop choice, rotation design and nutrient management. In practice, the choices to be made and the resulting outcomes are subject to a wide range of objectives and constraints. Objectives are economic as well as environmental, for instance sequestering carbon in agricultural soils or reducing nitrogen losses. Constraints originate from biophysical and institutional conditions that may restrict the possibilities for choosing crops or using specific cultivation and fertilization practices. To explore the consequences of management interventions to increase the supply of organic C to the soil on income and N losses, we developed the linear programming model NutMatch. The novelty of the model is the coherent description of mutual interdependencies amongst a broad range of sustainability indicators related to soil fertility management in arable cropping, enabling the quantification of synergies and trade-offs between objectives. NutMatch was applied to four different crop rotations subjected to four fertiliser strategies differing in the use of the organic fertilisers cattle slurry, pig slurry or compost, next to mineral fertiliser. Each combination of rotation and fertiliser strategy contributed differently to financial return, N emissions and organic matter inputs into the soil.Our model calculations show that, at the rotational level, crop residues, cattle slurry and compost each substantially contributed to SOC accumulation (range 200-450 kg C ha-1 yr-1), while contributions of pig slurry and cover crops were small (20-50 kg C ha-1 yr-1). The use of compost and pig slurry resulted in increases of 0.61-0.73 and 3.15-3.38 kg N2O-N per 100 kg extra SOC accumulated, respectively, with the other fertilizers taking an intermediate position. From a GHG emission perspective, the maximum acceptable increase is 0.75 kg N2O-N per 100 kg extra SOC accumulated, which was only met by compost. Doubling the winter wheat area combined with the cultivation of cover crops to increase SOC accumulation resulted in a net GHG emission benefit, but was associated with a financial trade-off of 2.30-3.30 euro per kg SOC gained.Our model calculations suggest that trade-offs between C inputs and emissions of greenhouse gases (notably N2O) or other pollutants (NO3, NH3) can be substantial. Due to the many data from a large variety of sources incorporated in the model, the trade-offs are uncertain. Our model-based explorations provide insight in soil carbon sequestration options and their limitations vis-a-vis other objectives.