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The intensive use of pesticide and plastic mulches has considerably enhanced crop growth and yield. Pesticide residues and plastic debris, however, have caused serious environmental problems. This study investigated the effects of the commonly used herbicide glyphosate and micrometre-sized plastic debris, referred as microplastics, on glyphosate decay and soil microbial activities in Chinese loess soil by a microcosm experiment over 30 days incubation. Results showed that glyphosate decay was gradual and followed a single first-order decay kinetics model. In different treatments (with/without microplastic addition), glyphosate showed similar half-lives (32.8 days). The soil content of aminomethylphosphonic acid (AMPA), the main metabolite of glyphosate, steadily increased without reaching plateau and declining phases throughout the experiment. Soil microbial respiration significantly changed throughout the entirety of the experiment, particularly in the treatments with higher microplastic addition. The dynamics of soil β-glucosidase, urease and phosphatase varied, especially in the treatments with high microplastic addition. Particles that were considerably smaller than the initially added microplastic particles were observed after 30 days incubation. This result thus implied that microplastic would hardly affect glyphosate decay but smaller plastic particles accumulated in soils which potentially threaten soil quality would be further concerned especially in the regions with intensive plastic mulching application. [ABSTRACT FROM AUTHOR]

Knowledge of the changes of soil properties and soil particle-size distribution (PSD) is important for quantifying soil quality and dynamics during natural succession. We applied multifractal theory to characterize the PSDs in five soil layers of nine croplands abandoned for less than 1 year, 2, 5, 7, 10, 15, 20, 30 and 35 years and evaluated the changes of soil organic carbon (SOC), total nitrogen (total N), total phosphorus (total P), soil texture and multifractal parameters [capacity dimension ( D ), entropy dimension ( D ), correlation dimension ( D ) and Hölder exponent of order zero ( α )] during natural succession on the Loess Plateau of China. Rényi spectra ( D ) and singularity spectra f( α) characterized the PSDs well and sensitively reflected the changes of heterogeneity of the surface soil (0-20 cm) during natural succession. SOC, total N and clay contents and the multifractal parameters increased significantly by the late stage of succession, mostly in the topsoil (0-10 cm). Natural succession thus effectively improved the soil physicochemical properties on the Loess Plateau of China, even though it was time-consuming. SOC and total N contents decreased with depth throughout the natural succession, but the multifractal parameters were higher in the topsoil only in the late stage. D and D were strongly and positively correlated with SOC and total N contents in the surface layers and with fine particles in all layers, suggesting that D and D may be sensitive and practical indices for quantifying changes in soil properties and erosion. [ABSTRACT FROM AUTHOR]

This article studies the soil moisture conditions of 30 years artificial Robinia pseudoacacia in the north of Shaanxi under different climate conditions in order to explore the relationship between soil moisture and impact factor of Robinia pseudoacaeia in this area, and variation characteristics of soil moisture in the Loess Plateau region. The results show: that soil moisture content decreases with increase of soil depth, and in 40-50 cm depth the jump point of moisture reduction appears significantly. Soil moisture was lower than the grorvth critical moisture in 5 samples to the north of Chunhua, and has different degrees of deficit. Soil moisture deficit degree was more than 50% in sandy loam and light loam soils such as Yulin, Shenmu and Suide. With the increasing of latitude, hoth of soil accumulative storage and net rainfall tends to decrease, but the relationship between them is significant correlation, indicating that that climate conditions are the major factors causing significant difference of soil moisture. [ABSTRACT FROM AUTHOR]

Abstract: This study examined the changes in soil properties and soil quality 30years after cultivated farmland was restored back to forest land in Loess Plateau, China. Specifically, organic matter, total nitrogen (N) and phosphorus (P), available N, P and Potassium (K) contents in soils were tested and analyzed. In addition, enzyme activities of α-amylase, saccharase, polyphenol oxidase, cellulase, urease, catalase and alkaline phosphatase were also investigated. The study area has mostly been restored, in the past 30years, back to grassland in some parts, and the other parts of forest lands of black locust, korshinsk peashrub, Chinese pine, mixed trees of Chinese pine and amorpha, and mixed trees of black locust and amorpha. Soil properties on a sloped farmland, located in the study area but has not had a chance to be restored, were tested and the result was treated as the soil properties of non-restoration. Soil properties of an 80-year old forest land of Chinese arborvitae were tested and the result was treated as that of a climax community. The study showed that after 30years of restoration, nutrients content in the soil of mixed forest of black locust and amorpha increased significantly. However, nutrients content in the soil of mixed forest of Chinese pine and amorpha decreased. As to soil enzyme activities, saccharase, cellulase, urease, catalase and alkaline phosphatase increased while polyphenol oxidase activity decreased compared to non-restoration and climax community soils. The study also found that the organic matter content was relatively low in the restored soils, compared with not-restored land. This may be caused by the high enzyme activity per unit of organic carbon in the soils of the study area which tends to help decompose and therefore decrease the organic matter in soil. [Copyright &y& Elsevier]

Abstract: Severe soil and water loss has led to widespread land degradation of the Loess Plateau, China. During the past two decades, significant efforts have been made to revegetate degraded soil in the region. However, a better understanding of the ability of plants to promote soil microbial processes is important for successful revegetation. The current study was conducted at the Dunshan watershed on the Loess Plateau, with the aim of evaluating the effect of different vegetation types on the microbial properties of rhizosphere soil. Six vegetation types were evaluated: two natural grassland (Artemisia capillaries and Heteropappus altaicus), two artificial (i.e. planted by humans) grassland (Astragalus adsurgens and Panicum virgatum) and two artificial shrubland (Caragana korshinskii and Hippophae rhamnoides) species; an area without vegetation cover was used as a control. The results indicated that the highest values of soil organic C, total nitrogen (TN), microbial biomass carbon (MBC), MBN, saccharase, urease, catalase and peroxidase were recorded for H. altaicus and A. capillaries; of basal respiration (BR), the MBN: TN ratio, alkaline phosphatase and polyphenol oxidase for A. adsurgens; and of the BR: MBC ratio for P. virgatum. A rhizosphere soil microbial index (RSMI) was obtained using principal component analysis, and metabolic quotient (BR/MBC), BR, urease, water-soluble C and cellulase were found to be most important for assessing rhizosphere soil quality. All revegetated soil showed higher RSMI compared with control soil, with soil under natural grassland species (H. altaicus and A. capillaries) recording the highest value. It was concluded that plant species under arid climatic conditions have different effects on the microbial properties of rhizosphere soil owing to their different root exudates and plant debris. In addition, natural grasslands are most effective for revegetation of the Loess Plateau. [Copyright &y& Elsevier]