The Study of Nitrogen Efficiency Indices of Canola (Brassica napus L.) under Different Green Manure Crops and Nitrogen Sources

Green manure is a crop used primarily as a soil amendment and a nutrient source for future crops. Leguminous green manure may add N to crop systems through biological fixation, and the slow release of N from decomposing green manure residues may be well timed with plant uptake. Leguminous and non-leguminous plants are used as green manures. Leguminous plants can form symbiotic associations with Rhizobium bacteria in order to atmospheric N fixation. This fact causes that the green manures, which their principal component are leguminous plant residue, added more nitrogen to the soil compared to non-legume. Muurinen et al. (2007) reported that strong N translocation from vegetative parts of the main shoot in wheat, which exhibited higher competition for N between vegetative and reproductive organs. Therefore, improved understanding of plant N requirements and dynamics, particularly biomass production efficiency (BPE) from vegetative parts among species and cultivars, is needed to determine better nitrogen use efficiency (NUE). So that the objective of this study was to determine the effects of legume and non-legume green manure crops in combination with different N fertilizer rates on nitrogen efficiency indices of canola.
In order to study the effect of different green manure and nitrogen sources on nitrogen efficiency indices of canola, a field experiment was conducted in the experimental farm of Agricultural Faculty of Shahid Chamran University of Ahvaz during 2013-2014 growing season. The experimental was carried out as split plot based on randomized complete block design (RCBD) with three replications. The main plot was different green manure including millet, barley, mungbean, intercropping of millet and mungbean, and fallow (without green manure application). The subplot treatments were different nitrogen sources at three levels including no nitrogen fertilizer (Control), 50 % chemical nitrogen biological nitrogen (Nitroxin) and 100 % chemical nitrogen. Nitrogen fertilizer was applied 200 kg per hectare in the form of urea. The plots of green manure were established on 6 Sep. 2010 and incorporated to the soil on 17 Oct. 2013. Then canola (cv. Hyola401) was planted on 10 Nov. 2013 and was harvested on 21 Apr. 2014. Each plot size was 6 m2 (2 m × 3 m) that consisted of 6 rows of canola plants. Grain yield was determined by harvesting from a 2 m2 area in each plot. All dry vegetative samples and also grains were first ground and then plant N concentration was determined by standard macro-Kjeldahl procedure. N content was calculated by multiplying the N concentration by dry weight. Analysis of variance was used to test the significance of data and means were compared with LSD test.
The results showed that the increasing nitrogen application had negative effect on efficiency indices except of nitrogen reliance index (NRI). The highest nitrogen reliance index (NRI) (0.46 kg per kg plant) was obtained at control (without green manure and 100% chemical nitrogen) and the lowest (0.16 kg per kg plant) was revealed at mungbean intercropping with integrated nitrogen application. The highest nitrogen use efficiency (NUE) (21.4 kg per kg), and nitrogen uptake efficiency (NUE) (1.04 kg per kg) were obtained at mungbean green manure and no nitrogen fertilizer, respectively. The highest nitrogen agronomic efficiency (NAE) (24.98 kg per kg) was revealed at millet-mungbean intercropping and nitrogen integrated management. Totally the results indicated the positive effects of biological and chemical combined fertilizer and green manure plants on yield increment and efficiency indices, and decreasing of dependency on chemical inputs that it is in the way and the goal of sustainable agriculture.