Effect of biochar addition on soil water and nutrient contents and yield formation of millet in loess arid region

The content of soil organic matter in loess arid region is low, and the limited resources of water and fertilizer in dry farmland lead to low water and nutrient use efficiencies. Biochar has the potential to regulate the soil porosity environment and the availability of water and fertilizer. Therefore, the related mechanisms of biochar promoting the grain yield and regulating the soil water and fertilizer transport in loess arid region are worthy of in-depth exploration. In order to clarify the effect of biochar addition on soil water and nutrient contents, and yield formation of millet in loess arid region in northern Shaanxi Province, "Jingu 21" was used in this study. Five levels of biochar application were applied, i.e. CK (0 t·hm⁻²), C1 (2 t·hm⁻²), C2 (4 t·hm⁻²), C3 (8 t·hm⁻²) and C4 (16 t·hm⁻²), and the same amount of carbon for each level was applied consecutively for 2 years. The results showed that (1) Adding proper amount of biochar could effectively increase soil water content, but excessive addition of biochar was not conducive to soil water storage and utilization. The soil water content under C3 at the jointing and maturing stages was significantly increased by 21.4% and 30.5% compared with CK, and of the water content under C4 decreased by 8.83% and 7.25% for respective growth stages compared with C3, but there was no significant difference. (2) Soil pH value, organic matter, ammonium, nitrate and available potassium contents under C4 increased by 4.28% - 29.4% compared with CK after two years of biochar application. The soil available phosphorus content increased first and then decreased with the increase of biochar application, and the available phosphorus content under C4 decreased by 7.27% compared with CK. (3) The addition of biochar effectively improved the biomass and yield of millet. Under C3, the above-ground biomass of millet at the mature stage increased by 17.8% compared with CK, and the yield of millet increased by 16.9% compared with CK. In conclusion, appropriate amount of biochar application can effectively improve the soil water and fertilizer nutrient contents in the loess arid region in northern Shaanxi, and consequently favorite the accumulation of grain biomass, the transformation of carbohydrate and yield gain.