Book of Abstracts
11th IFOAM Scientific Conference
11-15 August 1996, Copenhagen, Denmark
Dept. of Soil Science, Danish Institute of Plant and Soil Science, P.O. Box 23, DK-8830 Tjele, Denmark
Nutrient balances are a tool for evaluating the sustainability of agroecosystems, and they emphasize the fact that everything is interconnected in nature. A crucial point in organic farming is the fodder production, which is limited by the amount of plant nutrients available in the field. In order to fully understand the sustainability of a system it is therefore necessary to evaluate nutrient balances at the field level. Results from a factorial field trial in a six-year rotation are presented. Nutrient balances for N, P and K in the fields of four types of organic husbandries with different livestock densities (0.9 and 1.4 livesstock units/ha) and different types of organic manure (slurry and deep litter) are evaluated in relation to the objectives of optimizing plant production and minimizing nutrient loss. The results showed that leaching losses were of major importance for the nutrient balances. Nitrate leaching ranged from 12 to 100 kg/ha and was highest in the first year after ploughing in the grass-clover pasture, irrespective of livestock density or type of manure. Potassium leaching was very low and ranged from 2 to 6 kg/ha. Nitrogen balances showed a deficit in legume-containing crops, and the usefulness of the N balances was thus limited by the incomplete knowledge of nitrogen fixation in the grazed clover-grass fields.