A conceptual model of carbon stabilisation based on patterns observed in different soils

In principle, greenhouse gas emissions can be offset by increasing soil carbon stocks. Full utilisation of that potential, however, requires a good understanding of the controls on carbon stocks to identify factors that can be modified through management changes and distinguish those from factors that are inherent soil properties that cannot be modified. Here, we present a conceptual model of protected (or stabilised) carbon stocks in soils based on observations from two farms in New Zealand, and from a combined soils data set from observations from throughout New Zealand. These data showed that1) When other factors, such as climate, plant cover and pasture management, were identical, soil carbon stocks were highly, and linearly correlated with the soil's specific surface area estimated from soil water adsorption.2) The slopes of these relationships decreased with soil depth.3) Extrapolation of the relationships to zero specific surface area resulted in relatively small intercepts on the soil carbon axis. These intercepts decreased with soil depth.4) The intercepts were considered to correspond to unprotected labile carbon, with highest contents near the soils surface where most carbon inputs are received by soils.5) Together, these observations implied that virtually all protected carbon in the analysed soils was protected by the soil matrix rather than biochemically, and that mineral surface area was the functionally relevant key attribute that defined the soils' protective capacity.6) It implied that protected organic carbon, Cp, in a soil can be described as, where k is a simple constant, is the total carbon inflow rate into the soil, is specific surface area, and f(T, W, pH, Al, …) is a specific turn-over rate of protected carbon as a function of temperature, soil water, pH, aluminium concentration, or any other factors apart from soil texture that may affect soil-carbon turn-over rates.These observations improve our understanding of the important carbon-protection mechanisms in the soil, with significant implications for the optimal manipulation of carbon input rates into different soils to maximise overall soil carbon storage. They imply that overall carbon storage of soils could be enhanced by physically transferring any available carbon from soils with low to soils with high specific surface areas

Estimating the surface area of soils by measured water adsorption. Adjusting for the confounding effect of water adsorption by soil organic carbon.

Specific surface area can be a strong predictor of organic carbon (SOC) contents in soils. Specific surface area can be estimated reliably and cost-effectively from water adsorption by air-dry soil samples, but SOC itself can also adsorb water. For estimating the mineral component of specific surface area, it is, therefore, necessary to exclude water-adsorption by SOC. Here, we refer to “apparent specific surface area” for measurements that include water adsorption by both mineral soil and SOC. We used a mathematical approach to estimate water adsorption by SOC so that this component can be subtracted from measurements of apparent specific surface area.We used a dataset of apparent specific surface area and soil carbon at seven depths from 50 soil cores collected from a research farm in the Manawatu region in New Zealand. Both apparent specific surface area and SOC content decreased with soil depth with very high correlation (r2 = 0.98). We estimated the SOC contribution to apparent specific surface area from the slope of the relationship between changes in apparent specific surface area and SOC content. For our soils, the SOC contribution to apparent specific surface area was estimated as 0.43 ± 0.02 m2 mgC−1. This parameter allows apparent specific surface area measurements to be corrected for the water adsorption by SOC to calculate the functionally relevant mineral specific surface area

Psychiatric disorders and symptoms severity in preschool children with atopic eczema

Background: To compare with a control group the frequency of psychiatric disorders and severity of psychiatric symptoms in preschool children with atopic eczema