Effect of different nitrogen levels on yield components, yield and nitrogen use efficiency of two lentil cultivars in rainfed conditions

IntroductionLentil (Lens culinaris Medic.) is an important grain legume adapted to cool climates. It is cultivated on 155700 hectares in Iran with 94.7 % of this area under rainfed conditions. The average lentil yield in Iran is 1195 and 476 kg per hectare in irrigated and rainfed farms, respectively. Low productivity is due to use of local varieties, which have low yield potential, and poor agronomic management practices applied by the farmers such as limitation or inappropriate distribution of fertilizer. Nitrogen is an essential element for the growth of crops and its deficiency exists almost everywhere. It is the limiting factor in the crop growth more than any other element, unless use the nitrogen as a fertilizer. Despite the numerous advantages of nitrogen fertilizers, excessive consumption of nitrogen can cause pollution of surface and ground water through leaching and erosion and also increases costs. According to an adequate supply of nutrient elements by careful use of fertilizers, especially in poor soils, yield increases and nitrogen use efficiency improves. The objective of this study was evaluation of yield of two lentil cultivars under the influence of nitrogen fertilizer and also, investigation the nitrogen uptake, utilization and use efficiency to determine the best level of nitrogen fertilizer and cultivar for the study area.  Materials & MethodsThe experiment was conducted as split plot based on randomized complete blocks design with three replications at the Agricultural Research Station, Ferdowsi University of Mashhad, during growth season 2015-16. Nitrogen fertilizer (in three levels i.e. 0, 40 and 80 kg per hectare) and cultivar (Birjand and Robat) were in main plots and sub plots, respectively. Nitrogen fertilizer was applied as urea to the plots before sowing. The sowing date was 9th March in 2016. Sampling was done at harvest time and included pod number per plant, seed number per pod, 100 seed weight, seed yield, biological yield and harvest index. Percentage of biomass nitrogen were measured with the Kjeldahl method and the efficiency index calculated by using the following equation:NupE= Noff/ Ns­­NutE­­b= B/ NoffNutE­­s= Sw/ NoffNUE­­b= B/ NsNUEs= Sw/ Ns                                                                                                                            Where NupE is the nitrogen (N) uptake efficiency, Noff is the N in above ground dry matter, Ns is the soil N supply, NutEb is the N utilization efficiency based on biomass basis, B is the total above ground biomass at harvest, NutEs is the N utilization efficiency based on seed yield, Sw is the seed weight, NUEb is the N use efficiency based on biological yield, NUEs is the N use efficiency based on seed yield. Data were analyzed with the SAS software; obtained averages compared with LSD test at the 5% level. Results & DiscussionThe results showed that the interaction effect between nitrogen fertilizer and cultivar was significant on yield components, seed and biological yield. 40 kg nitrogen fertilizer per hectare and Birjand cultivar showed that maximum of pod number per plant (33.47), seed (338. 23 kg per hectare) and biological yield (3291.68 kg per hectare). Maximum of seed number per pod and 100 seed weight were obtained in treatment of non-use of nitrogen fertilizer and Birjand cultivar and treatment of 40 kg nitrogen fertilizer per hectare and Robat cultivar, respectively. Interaction effect between nitrogen fertilizer and cultivar was significant on nitrogen content of biomass, nitrogen uptake, utilization and use efficiency based on seed and biological yields. 40 kg nitrogen fertilizer per hectare and Birjand cultivar showed that maximum of nitrogen content of biomass and nitrogen uptake efficiency. The highest nitrogen use efficiency based on seed yield (3.39 kg seed per kg Ns) and biological yield (33.48 kg biomass per kg Ns) were obtained in treatment of non-use of nitrogen fertilizer and Birjand cultivar that the difference was no significant with the treatment of 40 kg nitrogen fertilizer per hectare and Birjand cultivar. Analysis of correlation showed that, yield and nitrogen use efficiency had positive and significant correlations with the pod number per plant and nitrogen uptake efficiency, respectively. Also, there was positive and significant correlation between nitrogen uptake efficiency and yield. ConclusionThe results of this study indicated that treatment of 40 kg nitrogen fertilizer per hectare and Birjand cultivar are able to achieve maximum yield and nitrogen use efficiency. However, Birjand cultivar is a late cultivar and requires the optimum planting date for cultivation in this region. According to the observed correlations, breeding of this plant should be cultivars that they absorb nitrogen with more efficiently, so that in addition to improving nitrogen use efficiency and reducing environmental pollution also yield increase.