Effects of fertilization practices on infiltration in Shajiang black soils

Infiltration is an important mechanism by which rain and irrigation water replenishes soil water to support plant growth. As a low-yield soil, the Shajiang black soil has high clay content with strong wedging structures. These structures hinder infiltration and water holding capacity of the soil. This implies that high percentage of water occurring on the soil surface is lost to evaporation or the water in the soil is lost to leaching, which either way results in low plant water use efficiency. Soil structure improvement was considered as the most effective strategy to increase water holding capacity and plant water use efficiency of Shajiang black soils. However, few approaches have been developed to ameliorate soil properties in the region. Returning crop straw to the soil is a recommended approach that is extensively used in China. However, the exact role of straw products after degradation in soil property improvement and water cycle has remained largely unknown. This study investigated how the addition of maize straw and coal fly ash to soils affected soil properties and water infiltration of Shajiang black soils. Using an in situ Lysimeter field device, the effects of fertilization practices on soil properties and soil water infiltration characteristics were investigated. The study used non-fertilization as the control (CK), and formulated fertilization (PF), formulated fertilization plus 7 500 kg·hm^-2 straw returning (PF+JG) and formulated fertilization plus 7 500 kg·hm^-2 coal fly ash application (PF+FMH) as the experimental treatments. Soil properties and water infiltration characteristics were determined using the double-ring infiltration method at the end of the 2-year field experiment. The results indicated that soil organic matter in PF+JG treatment increased by 18.01% and 11.18%, that in PF+FMH treatment increased by 8.92% and 2.61% over those in CK and PF treatments, respectively. Similarly, soil total porosity respectively increased by 13.89% and 12.46% in PF+JG treatment and by 5.87%, 4.56% in PF+FMH treatment over those in CK and PF treatments. But soil bulk density decreased by 12.90% and 4.48% in PF+JG treatment and by 11.29% and 2.98% in PF+FMH treatment over those in CK and PF treatments, respectively. Cumulative soil water infiltration respectively increased by 98.08% and 34.64% in PF+JG treatment and by 90.39% and 29.41% in PF+FMH treatment over those in CK and PF treatments, which was significant. Steady-state infiltration rates of PF+JG (1.18 × 10^-4 m·s^-1) and PF+FMH (1.13 × 10^-4 m·s^-1) treatments were 1.99 and 1.91 times higher than that of CK (5.92×10^-5 m·s^-1) and 1.35 and 1.29 times higher than that of PF (8.73 × 10^-5 m·s^-1), respectively. While significant positive correlations were noted between steady-state infiltration rate and soil organic matter content or total porosity (P < 0.01), steady-state infiltration rate was negatively correlated with soil bulk density (P < 0.05). The results suggested that the application of maize straw and coal fly ash was a useful alternative method for improving soil properties and increasing water infiltration capacity in Shajiang black soils.