Effects of combined application of straw biochar and nitrogen on soil carbon and nitrogen contents and crop yields in a fluvo-aquic soil

ObjectivesThe objectives of this study were to explore effects of combined application of maize straw biochar (BC) and nitrogen (N) on soil physical and chemical properties as well as crop yields in North China. This study could elucidate the responses of soil and plant to the BC and N application in a fluvo-aquic soil, provide a scientific evidence for efficient use of straw resources, and enhance soil fertility and crop production .

MethodsA two-factor split plot experiment was conducted to investigate the effects of the combined application of BC and N on soil nutrient, microbial biomass, and crop yields under a winter wheat-summer maize rotation in North China. The BC used in this study was produced from maize straw at pyrolysis temperature of approximately 450℃ and maximum temperatures were maintained for 1 h. The main plot was three BC rates, 0, 7.5 and 22.5 t/hm², and expressed as BC₀, BC_7.5, and BC_22.5, respectively. The subplot was four N rates, 0, 150, 225 and 300 kg/hm², and expressed as N₀, N₁₅₀, N₂₂₅, and N₃₀₀, respectively. Wheat was sown on October 9, 2014, and harvested on June 8 next year. Maize was sown on June 10, 2015, and harvested on September 28, 2015. The soil samples (0–20 cm) were collected after the harvest, and the contents of soil organic carbon (SOC), total nitrogen (TN), soluble organic carbon (DOC), ammonium (NH₄⁺-N), nitrate (NO₃^–-N), microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) were analyzed using regular methods.

ResultsBC rates significantly affected the contents of the soil nutrients, microbial biomass and crop yields (P<0.01). The contents of SOC, TN, DOC, N\rmO_3^ - -N and SOC/TN were significantly increased with the increase of the BC application rates (P<0.05) by 165.0%, 74.1%, 39.1%, 75.1% and 44.0%, respectively, compared to the BC₀. The contents of MBC, MBN, and crop yields with a BC rate of 7.5 t/hm² reache the largest value, and were increased by 49.2%, 57.6% and 46.1% compared to the BC₀, and the contents of the BC_22.5 were reduced by 12.1%, 7.3% and 9.7% compared to the BC_7.5 respectively. The contents of NH₄⁺-N were descended with the increase of the BC rates, the BC_7.5 and BC_22.5 were reduced by 18.4% and 23.7% compared to the BC₀ respectively. The contents of SOC, DOC, NH₄⁺-N, MBC and MBN had the greatest values at the N rate of 150 kg/hm², and were significantly increased by 29.7%, 22.9%, 44.8%, 79.4% and 115.3% compared to the BC₀, respectively. The crop yields in all N treatments were higher than the N₀, but there were no significant differences among the three N treatments.

ConclusionsThe N₁₅₀BC_7.5 treatment was more effective to improve soil fertility and maintain high crop yields in a short term, which could be used as an effective way of management practice. Further studies are needed to estimate its effective mechanisms and long-term effects under the combined application of BC and N.