Screening of rapeseed germplasms with low nitrogen tolerance and the evaluation of its potential application as green manure

Abstract

<p id="C3">Rapeseed (<italic>Brassica napus</italic> L.) is the major edible oil crop in China, and it is also a kind of crop for land use and maintenance, crop rotation, and fallow. With the promotion of green development in agriculture, rapeseed is highlighted with its high quality as green manure due to the characteristics of great biomass and adaptability. For the different industrial objectives of rapeseed cultivation, the nutrient demand characteristics of the existing rapeseed varieties determine the high recommended fertilization levels, whereas it cannot meet the needs of green manure with low fertilizer input. Therefore, the evaluation and screening of rapeseed germplasms with low nitrogen (N) tolerance can provide material support for breeding rapeseed cultivars as green manure. In this study, 73 rapeseed germplasms were planted at two N levels (low N and normal N) in the field experiment, the potential application as green manure of different rapeseed germplasms were evaluated by fresh weight, nutrient accumulation, and tolerance index at full flowering stage. Results showed that the change of fresh weight per plant for 73 rapeseed germplasms under low N conditions ranged from 29.33 g to 199.33 g, and the variation coefficient was 30.0%. Meanwhile, under low N stress, the change of N accumulation in shoot and root of 73 rapeseed germplasms were ranged from 48.67-360.43 mg and 4.21-67.46 mg per plant, and the variation coefficient were 31.0% and 53.0%, respectively. This mean that there were certain genetic variations biomass and nutrient absorption and accumulation ability among different rapeseed germplasms. Therefore, it was feasible to select the rapeseed germplasm with superior advantages as green manure. According to the comprehensive analysis of N efficiency and tolerance index of different rapeseed germplasms at full-bloom stage, 25 of 73 rapeseed germplasms had relatively strong tolerance to low N, while 17 germplasms had relatively poor tolerance to low N, belonging to low N sensitive type. Further analysis revealed that the fresh weight per plant, N accumulation, and N uptake efficiency of low N tolerance germplasms were significantly greater than those of low N sensitive germplasms under two N treatments, it could be used as potential green manure for further application. According to the calculation, the maximum amount of N returned to the field in the low N tolerance rapeseed germplasm was 80.2 kg hm^-2. Above all, the selected germplasms with great low N tolerance could be used as potential green manure rapeseed resources to be reserved and applied. In actual production, to better realize the industrial application goal of “the few fertilizers convert into the more green manure”, the application of low N tolerant rapeseed as green fertilizer can reduce the input of chemical fertilizer.