Accumulation of soil organic carbon in aggregates after afforestation on abandoned farmland

Zhong

et al. 2017

Sci Rep

Despite vital importance in soil conditioning and a proxy for arbuscular mycorrhizal (AMF), glomalin-related soil protein (GRSP) contribution to soil carbon and nutrients at vertical soil profiles and underlying mechanism were not well-defined yet. Thus, 360 soil samples were collected from 72 farmland 1-m soil profiles in northeastern China, and soil physiochemical properties, nutrients, glomalin characteristics, local climates were determined. Linear decreases of glomalin amounts were observed from the top to deep soils, and glomalin/SOC (glomalin ratio to total SOC) in the 80–100 cm soil (EEG, easily-extracted GRSP, 2.2%; TG, total GRSP, 19%) was 1.34–1.5-fold higher than did in the 0–20 cm soil. Different statistical analyses crosschecked that the lower pH and higher SOC usually accompanied with the higher EEG and TG, while EEG was more sensitive to climates; Moreover, glomalin was more physiochemical-regulated in the deep soils, but more nutrient-regulation was found in the surface soils. Structure Equation Model showed that soil depths and climates indirectly affected TG and EEG features through soil properties, except significant direct effects on EEG. In future, glomalin assessment should fully consider these for identifying the AMF importance in the whole 1-m profile, and our findings also favor degrade soil improvement from glomalin rehabilitation.

Section: Discussionmentioning

confidence: 99%

Glomalin contributed more to carbon, nutrients in deeper soils, and differently associated with climates and soil properties in vertical profiles

Zhong

et al. 2017

Sci Rep

Soil Science Society of America Journal

“…The SOC content was determined using the Walkley-Black method (Nelson and Sommers, 1982). Soil bulk density (D B ) was measured at the same depths using a stainless-steel cutting ring 5.0 cm high by 5.0 cm in diameter (Wei et al, 2013a(Wei et al, , 2013b. The cores were weighed after drying at 105°C for 24 h.…”

Section: Materials and Methods Sample Collection And Preparationmentioning

confidence: 99%

Determination of Soil Texture by Laser Diffraction Method

Yang

Zhang

et al. 2015

Self Cite

The laser-diffraction method (LDM) can rapidly determine soil particlesize distributions (PsDs), but LDM-derived PsDs cannot be directly used to classify soil textures by referring to the standards of the classical sievepipette method (sPM). Our objectives were to explore calibration models for converting PsD data from LDM (volume, %) to sPM (mass, %), and to evaluate the precision of textural classification by using LDM data. we determined the PsDs using both methods for 235 soil samples of various textures collected from three typical land uses, on the Loess Plateau of China. The LDM generally underestimated clay fractions by an average of 45.1%, and overestimated silt fractions by an average of 18.3% compared with sPM. Differences in PsD data between the two methods, indicated by coefficient Cs, increased with increasing clay contents for the 235 samples (P < 0.05). Three calibration models could, however, convert the clay, silt, and sand contents from the volume percentage (LDM) to the mass percentage (sPM). After the conversion, the mean coefficient C between the two methods decreased from 7.9 to 4.1% for the validation samples (n = 78). The distributions of soil textures within the usDA textural triangle agreed well in 71 of the 78 samples, for measured and converted PsD data. The three types of land use did not affect the differences between measured and converted PsD data (P > 0.05). soil textures can thus be rapidly determined by converting PsD data from the faster volume-based LDM to data equivalent to the mass-based sPM, independent of land-use type.

“…Similar to the concurrent measurements, separated measurements of 292 SOC and SIC also showed that fertilization and tillage practices could improve SOC accumulation 293 with an average rate of 37.3 g m -2 yr -1 (Fig. 4), and the increase in SOC is due to the fact that 294 fertilization practices could return more organic C from roots, litter, and organic manure to soils 295 (Meng et al, 2005;Yin & Cai, 2006;Zhang et al, 2006;Pan et al, 2006;Wei et al, 2012). 296 Counteracting depletion of SIC averaged at a rate of 17.1 g m -2 yr -1 (Fig.…”

mentioning

confidence: 99%

“…This overuse of 68 fertilizers has maintained crop production Song et al, 2007; Suo & Han, 69 2009;Sun & Suo, 2011), but also resulted in soil degradation and soil acidification (Guo et al, 70 2010). Furthermore, returning farmland to forest or grassland is a national policy to rehabilitate 71 the environment and soil erosion, and implementation of this policy over 10 years has improved 72 soil fertility and soil quality Wei et al, 2012;Wang et al, 2014a). In addition 73 to soil physiochemical changes, a lot of papers, books, and thesis papers have focused on the 74 changes of SOC, SIC, or both (as listed in references).…”

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confidence: 99%

See 1 more Smart Citation

Empirical model predictions and field measurements manifested divergent changes of SOC and SIC in calcareous soils in China

2017

Preprint

Background. Considerable amounts of calcareous soils exist in China and various management practices are used for improving their productivity; however, no holistic view is currently available of their effects on soil organic carbon (SOC) and soil inorganic carbon (SIC) pools. Our study aims to define co-current changes of SOC and SIC by using empirical model predictions and reviewing analysis of actual field data. Methods. Three datasets were compiled for the present study; the first was obtained from 9 soil survey reports from China and included data for SOC and SIC concentrations and various soil fertility parameters of soil N and available N; soil P and available P; soil K and available K; and soil pH and cation exchange capacity (CEC). These data were used for empirical prediction of SIC and SOC changes with changes in other soil properties via regression analysis. The second dataset comprised 111 data points from concurrent measurements of SOC and SIC from long-term fixed sites and paired sampling sites (long-term fertilization, tillage treatment, paired land-uses, degraded farmland afforestation etc), which were used to confirm the empirical predication. The third dataset comprised separated measurements of rates of changes in SIC (36 data points) and SOC (74 data points), and frequent distribution and averages were analyzed for finding changing rate differences. These datasets were used to determine the relative magnitude of rates of changes in SIC and SOC to identify the importance of co-inclusion of the two components for soil carbon budget estimation. Results. Empirical relationships between soil fertility parameters (total N and available N; total P and available P; total K and available K; and pH and CEC) and SOC were generally opposite to relationships between soil fertility parameters and SIC (p < 0.001), indicating that soil physicochemical changes as a result of management strategies may affect SOC and SIC in a divergent direction. A total of 111 concurrent measurements of SIC and SOC revealed that soil fertilization and tillage practices could increase SOC andlower SIC by 18% and 11%, respectively, compared to control practices. Similarly, the dataset comprising separated measurements showed that SOC changing rate averaged at 37.3 g m-2 yr-1(SOC accrual), and SIC changing rate averaged at -17.1 g m-2 yr-1(SIC loss), counteracting the SOC accumulation. Discussion. Changes in SIC are more complicated than those of SOC. In a semiarid region with abundant CO 2 and Ca 2+ , pedogenic formation of SIC was observed, while in a moist region (such as a karst land region) with sufficient water supply, dissolution-induced SIC loss in surface soils was frequently observed. Our findings highlight that SOC and SIC should be simultaneously included in the computation of soil carbon budgets to avoid false estimation of carbon changes as a result of using either SOC or SIC alone.