Increase effect of biochar on cotton yield and nitrogen use efficiency under different nitrogen application levels

【Objective】 Biochar has a strong ability of carbon sequestration, and can be used to improve soil fertility, and increase crop growth and nutrient utilizing efficiency. The influence of cotton straw and the biochar made from cotton straw on the yield and nitrogen use efficiency of cotton under different nitrogen fertilizer application rates was studied in this paper. 【Methods】 A complete 23 random field experiment was carried with cotton as material. Three carbon treatments: cotton straw 12 t/hm2(ST), biochar 4.5 t/hm2(BC) and no straw or biochar(CK); the three nitrogen rates(0, 300 and 450 kg/hm2, denoted as N0, N300 and N450) were completely modular designed. We collected cotton plants for determination of plant dry weight, nitrogen uptake at different growth stages of cotton(full budding, flower emergence, full flowering, full boll and boll opening), and the cotton yield at the cotton boll opening period. 【Results】 The dry matter weights and nitrogen uptakes of cotton were increased significantly by the addition of cotton straw and the biochar. Under low N input(N0), there are no significant differences in dry matter weights and nitrogen uptakes between the cotton straw treatment and the biochar treatment. Under the middle nitrogen level(N300), there is no significant difference either in the dry matter, but the nitrogen uptake in the biochar treatment is significantly higher than in cotton straw treatment. Under the high nitrogen level(N450), both the dry matter weight and the nitrogen uptake in biochar treatment are significantly higher than those in the cotton straw treatment. The cotton yields in the cotton straw and biochar treatments are significantly higher than in control. Under the no fertilization condition(N0), there is no significant difference in the cotton yields between the cotton straw treatment and the biochar treatment, but the cotton yields in the biochar treatment with nitrogen fertilization(N300 and N450) are significantly higher than those in the cotton straw treatments. In the middle nitrogen level(N300), the cotton straw and biochar treatments increase nitrogen use efficiency by 12.2% and 26.8% respectively, compared to the control treatment. On the other hand, when the high nitrogen level(N450) is applied, the improvement in nitrogen use efficiency under the biochar treatment is by 18.8%, but there is no significant difference of nitrogen use efficiency between the cotton straw treatment and the control treatment. 【Conclusions】 The interaction of biochar and nitrogen fertilizer could promote growth and the yield of cotton,and increase nitrogen use efficiency consequently