[Main principles of sampling and evaluation of surface water quality in watersheds exploited by agriculture]

agricultura agriculture agua superficial analyse de l'eau bassin versant calidad del agua czech republic eau superficielle legislation mathematical models muestreo nitrate nitrates nitratos normas norme nutrientes nutrients pollution de l'eau procesos de transporte en el suelo sampling saprofitismo saprophytism saprophytisme soil transport processes standards substance nutritive surface water transport dans le sol water analysis water pollution water quality watersheds