Accelerated wheat production in semi-arid developing regions: economic and policy issues.

condiciones ambientales condition de milieu consommation consumo consumption control de malezas environmental conditions farming systems fertilizantes nitrogenados herbicidas herbicide herbicides income ingresos labranza nitrogen fertilizers plant production politique de la recherche precios prices prix production costs rendement rendimiento research policies revenu statistics technologie technology tecnologia tillage travail du sol trigo weed control wheats yields