Urea/sodium hydroxide pretreatments enhance decomposition of maize straw in soils and sorption of straw residues toward herbicides

Because of the rigid crystalline structure and recalcitrant components, maize straw returned is slowly decomposed in soils. Straw residues are substantially accumulated in soils and pose detrimental impacts to crop plantation. Here we report the pretreatments of urea and NaOH (USH) to enhance maize straw decomposition in the field. The USH reagents interacted synergistically to destruct straw, mainly through breaking the rigid hydrogen bonding network and chemically hydrolyzing recalcitrant lignin. The synergy was evident for the USH reagents containing 6-8% urea and 0.1-1% NaOH under various temperature conditions (-20 °C to 25 °C). The USH (7%/0.1%) pretreatment resulted in notable enhancement (37%) of straw decomposition in the field within 6 months, superior to current biological-based treatments (6-28%). Moreover, this pretreatment posed no influence on the adsorption of straw residues collected at the early stage of decomposition (27 days) toward five commonly used herbicides. Those straw residues collected on 67 days and later exhibited high adsorption capacity, indicated by 0.5- to 4-folded increases in Kd values. Additionally, the impacts to soil pH and bacterial/fungal community were negligible. The USH pretreatments thus have practical interests in mitigating accumulation of straw residues in straw-returned soils.