Development of buffer methods and evaluation of pedotransfer functions to estimate pH buffer capacity of highly weathered soils

Abstract

The pH buffer capacity of a soil (pHBC) determines the amount of lime required to raise the pH of the soil layer from its initial acid condition to an optimal pH for plant growth and the time available under current net acid addition rate (NAAR) until the soil layer acidifies to a critical pH leading to likely production losses. Accurate values of pHBC can also be used to calculate NAAR from observed changes in soil pH. In spite of its importance, there is a critical shortage of pHBC data, likely due to the long period of time needed for its direct measurement. This work aimed to develop quick, simple and reliable methods of pHBC measurement and to test these methods against a slow (7-day) titration used as benchmark. The method developed here calculates pHBC directly from the pH buffer capacity of the buffer solution and the increase in soil pH and corresponding decrease in pH of the buffer solution following mixing and equilibration. The pHBC values calculated using Adams and Evans or modified Woodruff buffers were in accord with those measured by slow titration. Buffer methods are easily deployed in commercial and research laboratories as well as in the field. The advantage of using buffer solutions to calculate pHBC instead of lime requirement is the broad application of this soil property. The pHBC of a soil is an intrinsic property that would not be expected to need remeasurement over periods of less than decades. Recurring lime requirement can be calculated from the soil's pHBC, initial and target pH values. A large proportion of the variability in pHBC was explained by the soil organic carbon content. This relationship between pHBC and soil organic carbon content allowed us to develop local pedotransfer functions to estimate pHBC for different regions of Australia.

Contrasting pH buffering patterns in neutral-alkaline soils along a 3600 km transect in northern China

“…Whereas acid inputs are fairly well documented, the patterns of soil pHBC across landscapes are not (Yang et al, 2012;Wong et al, 2013). Soil pHBC regulates the effect of acid deposition on terrestrial ecosystems by influencing the extent of soil pH change (Magdoff and Bartlett, 1985;Lu et al, 2015;Nelson and Su, 2010).…”

“…Soil pHBC regulates the effect of acid deposition on terrestrial ecosystems by influencing the extent of soil pH change (Magdoff and Bartlett, 1985;Lu et al, 2015;Nelson and Su, 2010). Hence, measurement or estimation of soil pHBC is clearly beneficial for predicting the rate of soil acidification in response to predicted rates of acid deposition (Vet et al, 2014;Wong et al, 2013;Lu et al, 2015).…”

“…Under regions with higher temperature and lower precipitation, in which potential evapotranspiration greatly exceeds precipitation, carbonate tends to accumulate and thereby enhance soil pHBC in the surface soil layer (Tan, 2011), whereas in regions with higher precipitation, leaching processes prevent the accumulation of carbonate and change the soil acidification rates. However, the controls of soil pHBC in neutral-alkaline soils have not received as much attention as those in acidic soils (Yang et al, 2012;Wong et al, 2013). Geographical gradients can provide an exceptional opportunity to decipher the effects of global changing environments (i.e., soil variables, climatic variables, and human disturbance) on variations in soil pHBC, which is important for understanding the underlying patterns of nutrient fluxes and the biogeochemical mechanisms of the response of terrestrial ecosystems to environment changes.…”

Retention Mechanisms of Citric Acid in Ternary Kaolinite-Fe(III)-Citrate Acid Systems Using Fe K-edge EXAFS and L3,2-edge XANES Spectroscopy

“…Tropical soils generally support forest and woodland systems which preserve a large C pool 6 , thus playing a vital role in global C cycling. Many tropical soils are highly weathered and acidic (3.0~5.0) 7 8 , and their clay mineralogy is generally dominated by kaolinite 9 10 11 12 . The low pH of tropical soils helps maintain a relatively high concentration of multivalent cations in the soil solution, with Fe 3+ and Al 3+ typically ranging from several to hundreds of μM, depending on specific soil properties 13 14 15 16 .…”

Sulfate sorption measured by a buffering index over a range of properties of soils from south Western Australia

“…The final concentration of the extracting solution is 0.01 M CaCl 2 . (6) The solution soil mixture is tumbled for 48 h at 258C; pH is measured at 6, 24 and 30 h and, if necessary, adjusted to the original soil pH CaCl2 using varying amounts of 0.01 M HCl or NaOH depending on the soil's pH buffering capacity, which is related to the carbon content (Wong et al 2013). (7) Tubes are centrifuged at 2670 g for 5 min and then filtered using Whatman no.…”