Soil surface sealing by liquid dairy manure affects saturated hydraulic conductivity of Brazilian Oxisols

Liquid manure applied on the soil surface may alter its hydraulic conductivity by surface sealing. In this study, we evaluated the chemical and physical mechanisms of the surface sealing process acting in sandy clay loam and clayey soils after liquid manure application (LDM). Factors affecting surface sealing, such as LDM dosage, total solids content of LDM, straw cover, and time after LDM application, were also studied. The saturated hydraulic conductivity (Ksat) was determined before and 24 h and 7 days after LDM application, and the sealing index was calculated. The liquid dairy manure application on the soil surface promoted surface sealing in both soils; around 93% of sealing surface was due to physical mechanisms and around 7% chemical mechanisms. The application of LDM with 9.4% total solids (TS) promoted a greater sealing index (greater surface sealing) compared to LDM with 0% TS, mainly within 24 h of LDM application. Greater surface sealing was also observed with a higher LDM dose (60 m3 ha−1). Soil cover with 5 Mg ha−1 of straw resulted in a lower sealing index (lower surface sealing) than soil with 0 Mg ha−1 of straw. Sealing index was greatest at 24 h after LDM application for all treatments (solids content, LDM dose and soil cover) in both soils (clayey and sandy clay loam). The clayey soil was more susceptible to surface sealing after LDM application than the sandy clay loam. In practical terms, application of LDM with a high total solids content to bare soil when followed by rainfall 24 h after LDM application, enhanced susceptibility to surface sealing and, consequently, greater detrimental effect on surface water quality.