Dairy liquid manure and no-tillage: Physical and hydraulic properties and carbon stocks in a Cambisol of Southern Brazil

Application of liquid manure is often related to risks of nutrient losses by runoff and thus to the deleterious effects on water quality; but scarce is the information about the beneficial effects of liquid manure on soil physical conditions and its contribution in reducing runoff and nutrient losses in long-term, especially in no-tillage (NT) soils in tropics and subtropics. This study assessed the contributions of dairy liquid manure (DLM) on structural and hydraulic quality and on total organic carbon (TOC) stocks of a sandy clay loam Cambisol under NT, in Southern Brazil. The DLM was applied during 2 years, at rates of 0, 60, 120 and 180 m3 ha−1 year−1 (DLM-0, DLM-60, DLM-120 and DLM-180, respectively). In the 0–5 cm layer, the application of DLM-180 decreased soil bulk density (1.32 to 1.17 Mg m−3), increased macroporosity (0.24 to 0.32 m3 m−3), increased mean weight diameter of water-stable aggregates (1.59 to 1.94 mm), increased the larger macroaggregates (>4.00 mm), decreased the microaggregates (<0.25 mm) and increased nearly five times the saturated hydraulic conductivity (54 to 246 mm h−1), compared to unamended soil. Similar but smaller trends for those properties were observed in 5–10 cm, while no alterations occurred in 10–20 cm layer. Application of DLM increased the soil water sorptivity from 2.78 mm min−0.5, in unamended soil, to 10.34 mm min−0.5, in DLM-180-amended, and so the respective infiltration rate from 164 to 241 mm h−1. The total annual C addition (crops plus manure) increased almost linearly from 5.5 to 10.5 Mg ha−1 with increments in DLM rate, but increments in TOC stocks in the whole 0–20 cm layer were observed only between unamended (stock of 23.4 Mg C ha−1) and amended soils (average stock of 26.5 Mg C ha−1), and not among amended soils. In general, findings of structural and hydraulic improvements support the possibility of DLM application to diminish runoff and associated nutrient losses in coarse-textured NT soils in long-term, contributing thus to mitigation of water eutrophication problems. Additionally, the tendency for increments in TOC stocks due to DLM application might indicate a potential of this management practice into promoting C sequestration.