Fertilizer use on potato in relation to soil productivity in the up country areas of Sri Lanka

agricultural lime azufre chaux agricole crop yield cropping systems cultivation cultivo engrais pk fertilidad del suelo fertilisation fertilizantes pk fertilizer application fertilizers manejo del suelo mise en valeur du sol papa phosphorus potassium fertilizers pomme de terre potatoes pratique culturale rendement des cultures rendimiento de cultivos sistemas de cultivo soil fertility soil management soil types soufre sulphur type de sol