The Combined Effects of Water Management and Biochar Amendment on Soil Water Content and pH of Paddy Soil

Abstract

【Background】 Traditional rice production in paddy fields in subtropical regions in China is to keep the soil surface flooded. This is not only a waste of water resources but also acidifies the soil and leaks agrochemicals to water bodies. Improving water use efficiency and ameliorating soil acidity is a challenge facing sustainable rice production in these regions. 【Objective】 The purpose of this paper is to investigate the efficacy of using intermittent irrigation and biochar amendment to improve the ability of soil to hold water and deacidify paddy soil. 【Method】 The experiment was conducted in a rice-rice rotation field. It consisted of two irrigation treatments: continuous flooding (CF) irrigation and intermittent irrigation. Added to the intermittent irrigation were three biochar amendments by adding 0 (IF), 24 t/hm2 (LB) and 48 t/hm (HB) of biochar. In each treatment, we measured soil water content and soil pH during the growth season of both the early and late rice, as well as in the duration when the soil was temporally fallowed. 【Result】 Compared with CF, intermittent irrigation alone did not result in significant changes in soil water content due to the combined impact of precipitation and drainage. Amending the soil with biochar did not alter soil water content during the growth season of ether rice, but reduced it significantly when the soil was fallowed due to the fine texture of the biochar and structural change in the soil. The annual average soil water content under CF, IF, LB and HB treatments was 47.35%, 39.58%, 36.81% and 39.02%, respectively. Compared to CK, intermittent irrigation alone had no impact on soil pH when soil was fallowed but reduced it by 0.22 and 0.57 unit during the growth season of the early and the late rice, respectively. Biochar amendment deacidified the soil, increasing its pH by 0.23~0.68 unit in the early rice season and 0.17~0.60 unit in the late rice season, with the increase varying with biochar application rate. 【Conclusion】 Intermittent irrigation alone reduces soil pH, and combining it with biochar amendment, especially at a high amendment rate, can increase soil pH. These results have important implications for improving agricultural management and quality of paddy soils with rice-rice rotation as commonly cultivated in subtropical regions in south China.

Keywords

• water management
• biochar amendment
• double rice cropping
• soil water content
• soil ph