Comparisons between conventional and ecological farming systems at Ojebyn - Nutrient flows and balances

Nutrient balances of nitrogen (N), phosphorus (P) and potassium (K) in a full scale experiment with conventional and ecological farming systems at Ojebyn in northern Sweden, 1990-1994, were calculated with a nutrient flow model. There was a tendency of yearly increase in N-input to the conventional system through fertilizer and purchased concentrates. In the ecological system a similar, weaker, tendency reflects concentrate purchases. Both tendencies depend on increased milk production. Calculated N-fixation was, on average, twice as large in the ecological system, compared with the conventional one. Calculations on N, P and K in manure and urine were validated. In solid manure and urine the model underestimated N and P, whereas K was overestimated. The farm N balance was increasingly positive in the conventional system and negative in the ecological. The P balance was positive in both systems with a higher surplus in the conventional system. The K balance was increasingly positive in the conventional system, but close to being balanced in the ecological. The soil balances were more negative in the ecological system and less positive in the conventional system. The K-balance was clearly negative in the ecological, but more in balance in the conventional system. Conclusions are: (1) under existing circumstances ecological farming is possible without immediate DM yield reductions, but with negative effects on soil nutrient balances, (2) sustainability is measured more stringently by soil balance than by farm balance, (3) estimates of N-losses need to be adjusted for north Swedish conditions and (4) fertilization recommendations for P and K in northern Sweden ought to be reconsidered.