Search

High nitrous oxide (N2O) emissions (2–10% of fertiliser N) were observed previously from acid soils cropped with sugarcane (Saccharum officinarum) in Australia. We assessed the impact of lime, a nitrification inhibitor (NI, as 3,4-dimethylpyrazole phosphate, DMPP), and copper (Cu) on N2O emissions from an acid sugarcane soil in a laboratory experiment using (1) urea (U), (2) U + DMPP, (3) U + CuSO4.5H2O (U + Cu), and (4) U + DMPP + Cu. The treatments were applied to both an un-limed soil (pH 5.1) and a limed soil (pH 6.9) and incubated at 25 °C and 55% water holding capacity (WHC) for 28 d, and then increased to 90% WHC for another 8 d to favour denitrification. At 55% WHC, both the addition of the NI (U + DMPP) and the liming of the acid soil significantly decreased cumulative N2O emissions, due to significantly lower net nitrifications. Liming and DMPP decreased N2O emissions by 79% and 90%, respectively. However, where lime and DMPP were applied together, N2O emissions decreased by 94% compared to those in the un-limed (acid) U-treated soil. In contrast, the addition of Cu and the increase in water content to 90% WHC had no significant effect on N2O emissions. Therefore, the combined use of lime and DMPP provides the best option to decrease N2O emissions from the acid soil. [ABSTRACT FROM AUTHOR]

Lime [calcium carbonate (CaCO3)] has been used for acid soil amelioration of acid soils in Australia and elsewhere, but its effects on soil physical properties are not clear. Mechanisms responsible for the beneficial changes in the soil physical and structural properties of an acidic hardsetting soil in southern NSW, Australia, as a result of lime application were investigated. Changes in water-stable aggregation, a mechanical property, were related to changes in physicochemical properties, and soil organic carbon forms as a result of liming. The improved soil structure due to liming can be explained in terms of reduction in SAR (Sodium absorption ratio) and increase in EC (Electrical conductivity) (both lead to less dispersion) as well as increases in labile carbon (less slaking). The combined effects of reduced dispersion and slaking were responsible for the reduced bulk density and tensile strength of the hardsetting surface soil. These beneficial effects of liming on soil structural and physical properties were detectable 4 years after but not 18 years after lime application. [ABSTRACT FROM AUTHOR]

Acid soils threaten agriculture in Australia as well as in many parts of the world by reducing plant productivity. Surface-applied lime (CaCO3) moves into the root zone only slowly but the process can be considerably hastened in the presence of earthworms. In a laboratory experiment, the abilities of three earthworm species in incorporating lime into the subsoil and the mechanisms involved were investigated. Aporrectodea longa was the most effective in moving surface-applied lime, increasing subsoil pHCa by 1.1 units (from 4.0 to 5.1) in the 7.5–10 cm layer after only 6 weeks. Aporrectodea trapezoides and a native anecid, Anisochaetae sp., were less effective than A. longa, but still increased pHCa by 0.7 unit in the 7.5–10 cm layer. The extent of lime incorporation by the different earthworms was unrelated to burrow size and abundance, but significantly related to the increase in water stable aggregates (>250 μm) found in the earthworm-inoculated soils. The water stable aggregates, largely in the forms of earthworm casts and burrow wall material (drilosphere) had significantly higher pH (>6) than the bulk soil (4.0). The results suggest that significant amounts of surface-applied lime can be carried down the soil profile by the earthworms either via ingestion and subsequent deposition as casts at depth or by directly attaching to the body surface. [ABSTRACT FROM AUTHOR]