Reply to Elberling et al.'s (2013) comments on "Abiotic processes dominate CO₂ fluxes in Antarctic soils" (Soil Biol. Biochem. 53, 99-111)

A Letter to the Editor in response to an article B. Elberling, L.G. Greenfield, E.G. Gregorich, D.W. Hopkins, P. Novis, A.D. Sparrow Comments on “Abiotic processes dominate CO₂ fluxes in Antarctic soils” by Shanhun et al. Soil Biology & Biochemistry 53, 99–111 (2012). Soil Biology and Biochemistry, Volume 75, August 2014, Pages 310-311

The effect of irrigated land-use intensification on the topsoil physical properties of a pastoral silt loam

In Canterbury, New Zealand, there has been a widespread conversion of dryland sheep grazing to more intensive irrigated dairying. We determined the effects of these land uses on soil physical properties, and water release characteristics, on adjacent sites: a centre-pivot sprinkler-irrigated dairy farm site, a dryland sheep site, and a non-grazed, non-irrigated control site. Despite the Pallic Soil being well drained, greater soil compaction occurred at the dairy site than at other sites, to at least 30 cm depth. The dairy site typically had significantly lower total porosity and macroporosity, and greater bulk density and volumetric water content, than the other sites. Available water capacity varied but was greater at the dairy site (0–30 cm) than at the sheep site and control site. Further research is required across more farms and soils to confirm these results in other conditions

Land-use intensification and dairy effluent effects on soil water repellency and soil carbon of a silt loam topsoil

In Canterbury, New Zealand, there has been widespread conversion of dryland sheep grazing to more intensive irrigated dairying. We determined the effects of these land uses on soil carbon on a centre-pivot sprinkler-irrigated dairy farm site, a dryland sheep site, and a non-grazed control site. The dairy site had significantly greater carbon density and carbon storage at 10–20 cm and 0–30 cm depths than the sheep farm site. The dairy farm site had significantly greater carbon stock (equivalent soil mass method) than the sheep farm site at 10–20 cm depth. The dairy farm site intensification did not adversely affect soil carbon, including carbon stock by the equivalent soil mass method. The effects of dairy effluent application on soil water repellency and water movement were investigated. The dairy site had significantly greater subcritical repellency index than the sheep site and a dairy effluent site. Further research is required across more farms and soils to confirm these results in these land uses and under other management and climate conditions

Contrasting diel hysteresis between soil autotrophic and heterotrophic respiration in a desert ecosystem under different rainfall scenarios

Diel hysteresis occurs often between soil CO(2) efflux (R(S)) and temperature, yet, little is known if diel hysteresis occurs in the two components of R(S), i.e., autotrophic respiration (R(A)) and heterotrophic respiration (R(H)), and how diel hysteresis will respond to future rainfall change. We conducted a field experiment in a desert ecosystem in northern China simulating five different scenarios of future rain regimes. Diel variations of soil CO(2) efflux and soil temperature were measured on Day 6 and Day 16 following the rain addition treatments each month during the growing season. We found contrasting responses in the diel hysteresis of R(A) and R(H) to soil temperature, with a clockwise hysteresis loop for R(H) but a counter-clockwise hysteresis loop for R(A). Rain addition significantly increased the magnitude of diel hysteresis for both R(H) and R(A) on Day 6, but had no influence on either on Day 16 when soil moisture was much lower. These findings underline the different roles of biological (i.e. plant and microbial activities) and physical-chemical (e.g. heat transport and inorganic CO(2) exchange) processes in regulating the diel hysteresis of R(A) and R(H), which should be considered when estimating soil CO(2) efflux in desert regions under future rainfall regime