Contribution of soil mineral nitrogen in wheat production

A substantial amount of soil mineral nitrogen (Nmin) (NO3-N+NH4-N) exists i n the effective rooting depth of most profiles. However, soil Nmin is usual ly not taken into account in fertilizer recommendations for crop production . The level of preplant-soil Nmin in the Cukurova region of Turkey is consi derably high based on the high level of N application to many field and gre enhouse crops. Therefore, soil Nmin was determined in the profiles of the w heat-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 th e profile, and it needs to be taken into account in fertilizer N recommenda tions.