[Phosphorus and potassium in soil, and nutrient balances at ecological, integrated and conventional cultivation. Results from the cropping system experiment at Apelsvoll Research Center 1990-1996]

agricultura alternativa agricultura tradicional agriculture alternative agriculture traditionnelle alternative agriculture animal husbandry chimie du sol disponibilidad de nutrientes fertilidad del suelo field experimentation fosforo integrated plant production noruega norway nutrient availability phosphore phosphorus potasio potassium rendement rendimiento rotation culturale rotational cropping soil chemistry soil fertility traditional farming yields