Coupled effects of biochar use and farming practice on physical properties of a salt-affected soil with wheat–maize rotation

Abstract

Being carbon-rich and porous, biochar has the potential to improve soil physical properties, so does conventional farming practice. Here, a field trial was conducted to investigate the combined effects of biochar use and farming practice on the physical properties of a salt-affected compact soil for wheat–maize rotation in the Yellow River Delta region. Salix fragilis L. was used as feedstock to produce biochar in the field via aerobic carbonization at an average temperature of 502 °C, terminated by a water mist spray, for use as a soil amendment at 0, 1, 2, and 4 g kg−1 doses (CK, T1, T2, and T3, respectively). Farming practices included rotary tillage/straw returning for wheat sowing, spring irrigation, no-tillage seeding of maize, and autumn irrigation. Both cutting ring and composite samples of the soil were collected at four stages of wheat–maize rotation (22, 238, 321, and 382 d after the benchmark date of land preparation for wheat sowing) for the determination of soil properties by established methods. Rotary tillage/straw returning reduced soil bulk density (BD) from 1.48 to 1.27 g cm−3 (CK) and 1.14 g cm−3 (T3) and increased saturated hydraulic conductivity (Ks) from 0.05 × 10−5 to 0.75 × 10−5 cm s−1 (CK) and 1.25 × 10−5 cm s−1 (T3). This tillage effect on BD and Ks gradually disappeared due to the disturbance from the subsequent farming practice. Biochar use lessened the disturbance. At maize harvest, BD was 1.47 (CK) vs. 1.34 g cm−3 (T3), and Ks was 0.06 × 10−5 (CK) vs. 0.28 × 10−5 cm s−1(T3); in comparison with CK, T3 increased Na+ leaching by 65%, Cl− leaching by 98%, organic carbon content by 40.3%, and water-stable aggregates (0.25–2 mm) by 38%, indicating an improvement in soil properties. Biochar use and rotary tillage improved soil physical properties (BD, Ks) and favored soil aeration, water filtration, and salt leaching, which further helped the accumulation of soil organic carbon, the formation of water-stable aggregates, and the amelioration of salt-affected compact soil.