The response of wheat to nitrogen and phosphorus fertilizer under farmers conditions in Rahad [Sudan]

abonos fosfatados abonos nitrogenados application methods atelier pilote campo champ crop yield extension extension activities farming systems fields grande exploitation agricole large farms muestreo nitrogen fertilizers organic matter phosphate fertilizers pilot plants plant response rendement des cultures rendimiento de cultivos respuesta de la planta sampling soil sol suelo trigo vulgarisation wheats