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1. chinaXiv:201712.00322 [pdf]

Decomposition characteristics of organic materials and their effects on labile and recalcitrant organic carbon fractions in a semi-arid soil under plastic mulch and drip irrigation

Wu, Jinggui
Subjects: Geosciences >> History of Geosciences

Labile organic carbon (LC) and recalcitrant organic carbon (RC) are two major fractions of soil organic carbon (SOC) and play a critical role in organic carbon turnover and sequestration. The aims of this study were to evaluate the variations of LC and RC in a semi-arid soil (Inner Mongolia, China) under plastic mulch and drip irrigation after the application of organic materials (OMs), and to explore the effects of OMs from various sources on LC and RC by probing the decomposition characteristics of OMs using in-situ nylon mesh bags burying method. The field experiment included seven treatments, i.e., chicken manure (CM), sheep manure (SM), mushroom residue (MR), maize straw (MS), fodder grass (FG), tree leaves (TL) and no OMs as a control (CK). Soil LC and RC were separated by Huygens D’s method (particle size-density), and the average soil mass recovery rate and carbon recovery rate were above 95%, which indicated this method was suitable for carbon pools size analysis. The LC and RC contents significantly (P<0.01) increased after the application of OMs. Moreover, LC and RC contents were 3.2%–8.6% and 5.0%–9.4% higher in 2016 than in 2015. The applications of CM and SM significantly increased (P<0.01) LC content and LC/SOC ratio, whereas they were the lowest after the application of TL. However, SOC and RC contents were significantly higher (P<0.01) after the applications of TL and MS. The correlation analysis indicated the decomposition rate of OMs was positively related with LC content and LC/SOC ratio. In addition, lignin, polyphenol, WOM (total water-soluble organic matter), WHA (water-soluble humic acid), HSL (humic-like substance) and HAL (humic acid-like) contents in initial OMs played important roles in SOC and RC. In-situ nylon mesh bags burying experiment indicated the decomposition rates of CM, SM and MS were significantly higher than those of MR, FG, and TL. Furthermore, MS could result in more lignin derivatives, WHA, and HAL polymers in shorter time during the decomposition process. In conclusion, the application of MS in the semi-arid soil under a long-term plastic mulch and drip irrigation condition could not only improve soil fertility, but also enhance soil carbon sequestration.

submitted time 2017-12-18 From cooperative journals:《Journal of Arid Land》 Hits1356Downloads735 Comment 0

2. chinaXiv:201712.00323 [pdf]

Effects of long-term cultivation practices and nitrogen fertilization rates on carbon stock in a calcareous soil on the Chinese Loess Plateau

Chen, Zhujun
Subjects: Geosciences >> History of Geosciences

Soil organic carbon (SOC) and soil inorganic carbon (SIC) are important C pools in the Loess Plateau of Northwest China, however, variations of SOC and SIC stocks under different cultivation practices and nitrogen (N) fertilization rates are not clear in this area. A long-term field experiment started in June 2003 was conducted to investigate the SOC and SIC stocks in a calcareous soil of the Chinese Loess Plateau under four cultivation practices, i.e., fallow (FA), conventional cultivation (CC), straw mulch (SM), and plastic film-mulched ridge and straw-mulched furrow (RF), in combination with three N fertilization rates, i.e., 0 (N0), 120 (N120), and 240 (N240) kg N/hm2. Results indicate that the crop straw addition treatments (SM and RF) increased the contents of soil microbial biomass C (SMBC) and SOC, and the SOC stock increased by 10.1%–13.3% at the upper 20 cm soil depth in comparison to the 8-year fallow (FA) treatment. Meanwhile, SIC stock significantly increased by 19% at the entire tested soil depth range (0–100 cm) under all crop cultivation practices in comparison to that of soil exposed to the long-term fallow treatment, particularly at the upper 60 cm soil depth. Furthermore, moderate N fertilizer application (120 kg N/hm2) increased SOC stock at the upper 40 cm soil depth, whereas SIC stock decreased as the N fertilization rate increased. We conclude that the combined application of crop organic residues and moderate N fertilization rate could facilitate the sequestrations of SOC and SIC in the calcareous soil.

submitted time 2017-12-18 From cooperative journals:《Journal of Arid Land》 Hits1072Downloads705 Comment 0

3. chinaXiv:201712.00324 [pdf]

Determinants and rates of land degradation: Application of stationary time-series model to data from a semi-arid environment in Kenya

Mganga, Kevin; Nyariki, Dickson
Subjects: Geosciences >> History of Geosciences

The causes of land degradation in the African drylands have been shown to vary. Some researchers consider climate to be the major contributor to degradation, with anthropogenic factors playing a minor role. Others reverse the significance of these two factors. A third group attributes land degradation to climate and anthropogenic factors equally. This study was undertaken to establish the factors influencing land degradation in a semi-arid environment in southeastern Kenya and the rate of change in vegetation types for a period of 35 years (1973–2007). The reduction in grassland cover was used as an indicator of land degradation. Causes of land degradation were determined by a multiple regression analysis. A log-linear regression analysis was used to establish the rate of vegetation change. The multiple and log-linear regression analyses showed: (1) woody vegetation, livestock population and cultivated area to be the main contributors of reduction in grassland cover in the area, and (2) an increase in undesirable woody species, livestock population and cultivated area had a significant (P<0.05) negative effect on grassland vegetation. Increased human population, low amounts of rainfall and drought showed no significant negative effect on grassland vegetation cover. In conclusion, human and livestock population growth and increased agricultural land have contributed to intensive crop cultivation and overgrazing in the semi-arid lands. This overuse of the semi-arid rangelands has worsened the deterioration of the natural grassland vegetation.

submitted time 2017-12-18 From cooperative journals:《Journal of Arid Land》 Hits1088Downloads679 Comment 0