Nitrogen and sugar concentrations in the xylem exudate of field-grown maize at different growth stages and levels of nitrogen fertilization

abonos nitrogenados application rates azote azucares cereal crops chemical composition composition chimique cultivos de cereales dose d'application etapas de desarrollo de la planta nitrogen nitrogen fertilizers plant developmental stages sap savia stems sucres sugars tallo tige xilema xylem zea mays