Effects of Biochar Amendment on Bioavailable Nutrients in Paddy Soil

Abstract

【Objective】 Biochar is often used in soil amendment to improve soil quality and productivity. The objective of this paper is to investigate its efficacy in improving soil nutrients in a water-saving irrigated paddy soil. 【Method】 The experiment was conducted from 2018 to 2019 in a paddy field with controlled irrigation. It consisted of four biochar treatments: 0 (CK), 10 (CL), 20 (CM) and 40 t/hm2 (CH). In each treatment, we measured soil organic matter and mineral nitrogen. 【Result】 Amending the soil with biochar increased soil organic carbon and the increase was in the order of CH>CM>CL>CK. The impact of biochar amendment on soil mineral nitrogen varied. Compared to CK, CH, CM and CL increased ammonium by 1.52, 0.61 and 0.39 g/kg, respectively, in 2018, while reduced them by 2.01, 1.71 and 0.99 g/kg, respectively, in 2019. After fertilizer application at the tillering stage, CK saw the fastest increase in ammonium, while the ammonium in other treatments was comparable. After fertilizer application at the spiking stage in 2019, ammonium content was comparable with that in 2018, and its content in other treatments in 2019 was ranked in the order of CK>CL>CM>CH. The two-year experiment showed that CH, CM and CL reduced nitrate content by 32.34%, 19.45% and 9.21%, respectively, compared to CK. 【Conclusion】 The effect of biochar amendment on soil organic carbon in the water-saving irrigated paddy field was positively correlated with the biochar amount, but decreased as time elapsed. The biochar increased ammonium content only at the early stage after the amendment, but it reduced nitrate nitrogen content. Nitrate content was negatively correlated with biochar amendment amount. The biochar slows down the increase of ammonium following fertilization, thereby reducing nitrogen loss.

Keywords

• water saving irrigation
• biochar
• paddy field
• soil nutrients