Comparing the effect of different green manure crops and nitrogen rates on wheat (Triticum aestivum L.) by nitrogen efficiency indices

The green manure crops are one of the most important organic sources of nitrogen in agronomy. In order to evaluate of the influence of nitrogen rates and green manure crops by nitrogen efficiency indices a field experiment was conducted in Agricultural Faculty of Shahid Chamran University in 2010-2011. The experimental design was split-plot based on randomized complete block with 3 replications. The main plot included 4 nitrogen rates (i.e. 0, 50, 100 and 150 kgN.ha-1) and the sub-plot included 6 green manure crops (i.e. fallow, millet, sesbania, amaranth, cowpea and mung bean). Our results showed that, green manure crops had a significant effect on wheat grain yield. This effect was different between legume and non-legume green manure crops. But, the effect of green manure crops decreased by increasing indices in nitrogen rates. At nitrogen points of view, the best indices for evaluation of nitrogen effect were nitrogen balance, nitrogen reliance and nitrogen use efficiency indices, respectively. Also, at the green manure point of view, the best indices for evaluation of green manure crops were nitrogen balance index, nitrogen uptake and nitrogen utilization indices, respectively. In addition, the nitrogen reliance index had the highest positive correlation with grain yield. Over all, it seems that attention to traditional production criteria (i.e. grain yield) is not adequate and other eco-physiological criteria’s such as nitrogen efficiency indices must be taken into account.