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 syst ems at Ojebyn in northern Sweden, 1990-1994, were calculated with a nu trient flow model. There was a tendency of yearly increase in N-input to the conventional system through fertilizer and purchased concentrat es. In the ecological system a similar, weaker, tendency reflects conc entrate purchases. Both tendencies depend on increased milk production . Calculated N-fixation was, on average, twice as large in the ecologi cal system, compared with the conventional one. Calculations on N, P a nd 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 nega tive in the ecological. The P balance was positive in both systems wit h a higher surplus in the conventional system. The K balance was incre asingly positive in the conventional system, but close to being balanc ed in the ecological. The soil balances were more negative in the ecol ogical system and less positive in the conventional system. The K-bala nce was clearly negative in the ecological, but more in balance in the conventional system. Conclusions are: (1) under existing circumstance s ecological farming is possible without immediate DM yield reductions , but with negative effects on soil nutrient balances, (2) sustainabil ity is measured more stringently by soil balance than by farm balance, (3) estimates of N-losses need to be adjusted for north Swedish condi tions and (4) fertilization recommendations for P and K in northern Sw eden ought to be reconsidered.