Biochar application strategies mediating the soil temperature, moisture and salinity during the crop seedling stage in Mollisols.

It is well known that biochar remarkably changes the fertility and quality in degraded soils, however, it's still not clear how homogeneous application (HA) and bottom concentrated application of biochar (CA) influences soil moisture (SM), soil temperature (ST) and salts during crops seedling stage. In this study, both HA and CA combining with four levels of 0 (CK), 10 (CA1/HA1), 20 (CA2/HA2) and 40 t ha (CA3/HA3) were used to reveal how biochar affects SM, ST and soil electrical conductivity (EC) at seedling stage (spring) of maize in moderately degraded Mollisols. The results showed that, the speed of daily ST increase was only significantly slower in CA1 than in CK during the warming stage, performing a "hysteresis effect". Compared with CK, SM and EC were significantly reduced by 32.9 % and 52.9 % in CA3, while increased by 30.4 % and 20.7 % in HA3 during the whole seedling stage. Between the SM/EC and biochar application amount, there was a negative linear relationship in CA, while was a quadratic function relationship in HA during the whole seedling stage. SM (14.49-29.72 %), EC (0.15-0.38 ms cm) and ST (14.86-19.31 °C) were higher in CA1 and HA3 than other treatments in rainfall and drought conditions. DSSA-CERES-maize model adequately simulated the effect of biochar on ST change during maize seedling (nRMSE≤22.6 %, d ≥ 0.59) by integrating initial soil conditions, meteorological data, crop management data, and soil physicochemical properties and crop growth indexes affected by biochar. Generally, HA3 and CA1 was beneficial for improving soil water retention and reducing salt ion leaching, while CA3 accelerated soil drought and increased salt ion leaching during maize seedling stage in Mollisols. The results of this study can provide guidance for the application of crop models in biochar application.