Evaluation of nitrogen uptake and use efficiency in wheat cultivars (Triticum aestivum L.) under Kermanshah weather conditions

Nitrogen is the most important mineral nutrient for crop growth and development that improve quality and quantity of yield. It is used in modern agroecosystems to maximize yields. In harvest time, about 40 to 60% of applied nitrogen to the fields must be compensated by different fertilizers. Nevertheless, only 30 to 50% of consumed nitrogen is taken up by the crops and high amount of it is lost. Improved economic cost and environmental concerns augmented managing use of fertilizers. Improvement of nitrogen use efficiency has become an urgent target in crop production for efficient nitrogen utilization, maximum energy saving and productivity. In the sustainable agriculture approaches, there are several ways for increasing nitrogen use efficiency such as selection of suitable varieties. There is about six million hectare of wheat in Iran. Kermanshah Province with 6.4% of cultivation area and 6.6% of wheat production is the fifth place in Iran. In this province consumes large amounts of N fertilizers annually in the wheat agroecosystem. Therefore, the aims of this study were evaluating nitrogen uptake and utilization efficiency, and final nitrogen use efficiency in the wheat production system under Kermanshah weather condition. A split-plot experiment based on the randomized complete block design with three replications was conducted in the Campus of Agriculture and Natural Resources Field at Razi University under Kermanshah weather condition during 2015-2016. The experiment treatments were four levels of nitrogen fertilizer rate (90, 180, 300, 360 kg ha-1 of urea) as main-plot and four wheat varieties (Parsi, Zare, Pishgam and Orum) as sub-plot. The evaluated traits were included total dry weight yield, grain yield, biomass nitrogen content, nitrogen uptake efficiency (NUpE), nitrogen utilization efficiency (NUtE) and nitrogen use efficiency (NUE). Data analysis was done by SAS software (Ver 9.4) and means comparison by LSD tests were also carried out at the level of 5%. The results showed that under nitrogen fertilizer rate treatments, Pishgam variety in comparison with other varieties had the most satisfying ecophysiological characteristics. Regardless of studied varieties, by increasing the rate of urea fertilizer from 90 to 360 kg ha-1 total dry weight yield (65.9%) and grain yield (73.1%) were improved. In this situation, Pishgam variety had the highest grain yield (37.4%) compared to other varieties. The highest and the lowest grain yield were related to Pishgam variety (8950 kg ha-1) in 360 kgurea ha-1 treatment and Orum variety (1264 kg ha-1) in 90 kgurea ha-1 treatment, respectively. The results also showed that the highest NUpE observed in the lowest level of fertilizer rate for Zare variety (0.7 kg Nuptake/kg Nsoil+applied) and the lowest NUpE observed in the highest level of fertilizer rate for Orum variety (0.26 kg Nuptake/kg Nsoil+applied). The greatest and the lowest NUtE were for Pishgam variety (59 kg grain/kg Nuptake) in 90 kgurea ha-1 treatment and Orum variety (37 kg grain/kg Nuptake) in 360 kgurea ha-1 treatment, respectively. In relation to NUE, Pishgam variety had the highest value (36 kg grain/kg Nsoil+applied) under 90 kgurea ha-1 treatment and Orum variety had the lowest value (10 kg grain/kg Nsoil+applied) under 36090 kgurea ha-1 treatment. Our results also indicated that grain yield had a significant positive correlation with nitrogen content at anthesis and maturity while there was a significant negative correlation with NUpE and NUE. The relation of grain yield with  NUtE was positive and no significant. The results showed that most of traits of wheat varieties such as grain yield and total dry weight yield were improved by increased nitrogen fertilizer rate. But, evaluation of traits related to nitrogen efficiency showed that NUE reduced by increasing of nitrogen fertilizer rate for all wheat varieties. The NUpE compare to NUtE had more effect on NUE. The grain yield had a significant negative correlation with NUpE and NUE but it had a positive correlation with NUtE. Although, breeding of varieties with higher NUtE can be cooperate an effective role in improvement of NUE but it seems that emphasis on nitrogen management consumption methods can be more effective.