Biochar And Slow Release Urea Effects On Root Morphology, Grain Yield, Nitrogen Uptake And Utilization In Brassica Napus

Low nitrogen (N) utilization efficiency is a serious problem in rapeseed production. Slow-release urea (SRU) or the combined application of slow-release urea and common urea could enhance N utilization, but this effect is limited and long-term N fertilizer application would lead to soil acidification. Biochar has the potential to effectively improve acid soil and increase N utilization efficiency. A pot experiment was conducted to investigate the effects of the combined application of biochar and different urea on the root morphology, grain yield, and nitrogen uptake and utilization of rapeseed. The two-factorial complete randomized block design was adopted with three schemes of urea (100% common urea, 100% slow-release urea, and 60% common urea and 40% slow-release urea, named UR, SRU, and combined (60%+40% SRU), respectively), and three biochar levels (0, 2 and 4% of the soil weight, named C0, C1 and C2, respectively). Biochar was found to significantly affect rapeseed root morphology, grain yield, nitrogen uptake and utilization when compared with no biochar, but these effects varied with different urea and biochar application rate. C1 combined with 60%+40% SRU significantly promoted the diameter of root crown, total root volume, average root diameter, total nitrogen accumulation (TNA), and nitrogen-use efficiency (NUE); C1 combined with UR also significantly increased the total root volume, total root length, and average root diameter of rapeseed. However, C2 combined with UR and 60%+40% SRU, and the combined application of biochar (C1 and C2) and SRU, had an inhibitory effect on root morphology, nitrogen uptake and utilization, and yield due to the slow release effect of biochar on available nitrogen. The diameter of root crown, total root volume, total root surface area, average root diameter, TNA, NUE, effective pod number, number of grains per pod, and yield were highest under the combined application of 60%+40% SRU and C1. NUE and yield of 60%+40% SRU+C1 treatment increased by 12.36-63.68% and 2.82-46.59%, respectively, than with urea application only. This combination may be an effective mean to further improve the yield and NUE of rapeseed in dryland in southwest China. (C) 2020 Friends Science Publishers