Quantified and integrated crop and livestock production analysis at the farm level : exploring options for land use of mixed farms on heavy limestone soils south of Malang, East Java, Indonesia

To develop adequate and sustainable land use plans, a clear assessment of the potential of the land and of the existing farming systems, as well as an identification of ways to attain these potentials is required. The agricultural system in the limestone area south of Malang is classified into different land units, land uses and livestock units. Land uses include a further distinction into agro-forestry system and annual crop. Simulation models are used as a tool to explore the production potential of crops and livestock. Existing crop simulation models are used and adjusted to the situation at hand. A new livestock simulation model is developed that includes major farm household influences, particularly the influence of land and land use on the feed resource and on livestock production. The model considers also the seasonality of feed availability; feed is quantified on a monthly basis. Two production orientations, with their specific technologies, were distinguished; low external-input agriculture (relying on manure only) and yield-oriented agriculture (relying on inorganic fertilizers only). The present crop and livestock productions are far below the potentials, as were explored with the simulation models. Constraints to agricultural production in the research area are high erosion, a low soil organic matter and a declining natural soil fertility. Hence options for land use are explored which focus on biophysical sustainability. The latter is defined here as avoiding excessive erosion, at least maintaining the present soil organic matter content of 2% and maintenance of a closed balance of the most limiting resource.Systems with cattle, more perennials and yield-oriented agricultural systems leave more biomass than current cropping thus creating more cover, litter and mulch. An increase in the use of inorganic fertilizers seems the only viable direction towards more biomass production. Increased fertilizer use will improve the quantity and quality of crop yields as well as of crop residues for animal husbandry. Since 100% of crop residues never will be used in animal husbandry, effort should be made to return the left-overs to the soil in order to maintain or increase the soil organic matter content, i.e. better residue management. The extra manure both in terms of quantity and quality will also contribute to the latter goal. Finally, the higher soil organic matter content will improve the physical state of the heavy clay soils thus improving their water holding capacity, it will lower the soil's erodibility and improve nutrient use efficiency. So, use of inorganic fertilizers will trigger a cascade of effects that all point in the direction of a more sustainable use of the natural resources.