Modification of Soil Physical Properties by Maize Straw Biochar and Earthworm Manure to Enhance Hydra

The deterioration of soil physical properties had led to a decrease in soil–water availability in facility agriculture. Thus, an experiment was set up with five soil treatments of 0% (CK, No additives), 3% biochar (BA3, Mass ratio), 3% earthworm manure (QA3), 5% biochar (BA5), and 5% earthworm manure (QA5) to investigate the effects on soil physical properties and hydraulic characteristics under greenhouse conditions. The physical properties of soil including the soil bulk density (BD) and total porosity (TP) were measured; the results showed that BA5 provided the lowest soil BD (1.24 g·cm−3) and the highest TP (53.09%) and was 13.8% higher than CK. More importantly, the saturated hydraulic conductivity (KS), field capacity (FC), permanent wilting point (PWP), and available water content (AWC) of the soils treated with biochar and earthworm manure were significantly higher than those of CK. At the same application rate, the effect of biochar on soil–water permeability and water-retention capacity was significantly higher than that of earthworm manure, in which the soil–water-characteristic curve (SWCC) showed that as BA5 > BA3 > QA5 > QA3 > CK, the FC and AWC increased from 28.90% and 14.13% under CK, respectively, to 40.73% and 21.91% under BA5, respectively; and the KS, FC, PWP and AWC of BA5 increased by 45.93%, 40.91%, 27.46% and 54.96% compared with CK, respectively. The results revealed that the improvement of the soil TP was conducive to the enhancement of the soil KS and FC, enhanced the soil–water permeability and the water-retention capacity, and ultimately increased the AWC. From the perspective of improving the facility soil and economic benefits, the application of 5% biochar is considered to be the most beneficial.