Effect of Tillage Practices and Nitrogen Rates on Nitrogen Use Efficiency and Nitrogen Nutrition Index of Wheat in a Calcareous Soil (Case Study: Zarghan Region, Fars Province)

The goals of study were to evaluate the combined effects of tillage practices, corn residues, and nitrogen (N) rates for improving nitrogen use efficiency (NUE) and protecting yield performance of wheat in arid and semi-arid regions of southern Iran.  

The experiment was conducted as split split-plot based on randomized complete blocks design with three replications in the Zarghan Field Station, Agriculture and Natural Resources Research and Education Center of Fars Province during two cropping seasons (2015-17). The experimental treatments included tillage practices (Conventional tillage, CT; Reduced tillage, RT; No Tillage, NT) as main plots, with and without corn residue (at 30% residue retained and removed) as sub plots, and pure N rates (0, 101, 152, and 202 kg N ha-1 from Urea source) as sub sub-plots.  

After 2 years, wheat yields (5266 kg.ha-1) were tended to be increased with increasing N rates from 101 to 202 kg N ha-1 under RT with corn residue retention. Likewise, the increasing N rate at 202 kg.ha-1 can be increased apparent recovery efficiency of N (AREN) and nitrogen uptake efficiency (NUpE) under the reduction of soil tillage operations when crop residue retained. In the contrast, the highest physiological and agronomic efficiency of N (PEN and AEN, respectively) (58.18 and 19.31 kg.kg-1, respectively) were obtained by CT and RT methods with 101 and 152 kg N ha-1, respectively. Nitrogen nutrition index values <1, around 1, >1 were recorded at <152, 152, >152 kg ha-1 of N applied, respectively.  

Our research has shown that replacing RT with CT and/or NT with corn residue retention and 152 kg N ha-1 can greatly increase NUE especially AEN and PEN, improve NNI, and protect wheat grain yield under wheat- and corn in a rotation.