Preplant Soil Mineral Nitrogen for Fertilizer Recommendations for Wheat in Southeastern Turkey.

Preplant soil mineral nitrogen (Nmin, NO3-N + NH4-N) is widely used in N-fertilizer recommendations. We tested this approach in a large wheat-growing area in Turkey. Prior to planting, soil samples from the profile (0-30, 30-60 and 60-90 cm) were taken and analyzed for NO3-N and NH4-N to determine readily available Nmin. Soil samples (18 in 2007, and 36 in 2008) were taken from farmers’ wheat fields in the irrigation district. Plant samples were also colleted to determine N uptake. There was considerable amount of Nmin (72 to 120 kg Nmin ha-1) in the effective rooting depth (0-90 cm) in both years. The wheat yield and total plant N uptake by grain and the biomass were significantly increased by the higher values of Nmin in the profile, especially in 2007. Even though soil types and wheat genotypes grown in the irrigation District are different, this meaningful relationship between soil Nmin and yield and N uptake suggest considering preplant soil N in fertilizer recommendations and using less N fertilizers, thus contributing to increase use efficiency. The approach could be widely used in Turkey.