Phosphorus studies in the lowland rice soils of the mid-country wet zone [fertilizer, Sri Lanka]

agricultural chemicals agronomic characters anthropogenic soil types arroz asia asie cereales cereals crops cultivos cultivos de grano economic plants engrais environment environnement fertilidad del suelo fertilizantes fosfatados fertilizers fosfatos grain crops inorganic compounds medio ambiente paddy soils phosphate phosphate fertilizers phosphates plantas plante plante de culture plants productividad productivity produit agrochimique profitability rendement rendimiento rentabilidad rice riz sales salts sel site factors soil fertility soil types sri lanka type de sol yields