Optimizing Nitrogen Recommendations for Tillage and Corn Residue Management in Irrigated Wheat, Southern Iran

Abstract

ABSTRACT In southern Iran, intensive tillage operations and residue removal have been the major cause of declining crop productivity and nitrogen-use efficiency (NUE). A 2-year field experiment (2016–2017) was conducted to test four nitrogen (N) rates (0, 101, 152, and 202 kg N ha−1) and tillage practices (conventional, CT; reduced, RT; and no tillage, NT) effects on irrigated wheat (Triticum aestivum L.) grown with or without corn (Zea mays L.) residue removal, using a split-plot design with three replications near Shiraz, Iran. After 2 years, wheat yields were tended to be increased with increasing N rates from 101 to 202 kg N ha−1 under RT with residue retention. Increasing N rate decreased NUE values particularly N physiological efficiency (PEN). Likewise, the lowest NUE was obtained under NT, while RT and CT either showed similar effects or RT was superior over CT. Furthermore, the NNI value around 1 was obtained at 152 kg N ha−1 under RT, when crop residues were retained or removed. Our research has shown that replacing CT with conservation tillage (especially RT) with residue retention and 152 kg N ha−1 can greatly protect wheat yield and optimize NUE values under wheat- and corn in a rotation, but it is based on the short-term results and evaluation of long-term experiment is highly recommended.