CONTRIBUTION OF SOIL MINERAL NITROGEN IN WHEAT PRODUCTION

A substantial amount of soil mineral nitrogen (Nmin) (NO₃—N + NH₄—N) exists in the effective rooting depth of most profiles. However, soil Nmin is usually not taken into account in fertilizer recommendations for crop production. The level of preplant-soil Nmin in the Cukurova region of Turkey is considerably high based on the high level of N application to many field and greenhouse crops. Therefore, soil Nmin was determined in the profiles of the wheat-field experiments, which were conducted at eight different locations. Nitrogen was applied in six rates as 1/2 at planting, 1/4 at tillering and 1/4 at booting stages. Wheat-grain yield was determined following harvest. Even though the yield was increased by the added rates of N, it was greater where the preplant soil Nmin values were measured as relatively high. Two years of results show that there are substantial amounts of soil Nmin in the profile, and it needs to be taken into account in fertilizer N recommendations.