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Soil organic carbon (SOC) is the most often reported attribute and is chosen as the most important indicator of soil quality and agricultural sustainability. In this review, we summarized how cultivation, crop rotation, residue and tillage management, fertilization and monoculture affect soil quality, soil organic matter (SOM) and carbon transformation. The results confirm that SOM is not only a source of carbon but also a sink for carbon sequestration. Cultivation and tillage can reduce soil SOC content and lead to soil deterioration. Tillage practices have a major effect on distribution of C and N, and the rates of organic matter decomposition and N mineralization. Proper adoption of crop rotation can increase or maintain the quantity and quality of soil organic matter, and improve soil chemical and physical properties. Adequate application of fertilizers combined with farmyard manure could increase soil nutrients, and SOC content. Manure or crop residue alone may not be adequate to maintain SOC levels. Crop types influence SOC and soil function in continuous monoculture systems. SOC can be best preserved by rotation with reduced tillage frequency and with additions of chemical fertilizers and manure. Knowledge and assessment of changes (positive or negative) in SOC status with time is still needed to evaluate the impact of different management practices.

Soil degradation that results from erosion, losses of organic matter and nutrients, or soil compaction are of great concern in every agricultural region of the world. The control of soil erosion and loss of organic matter has been proposed as critical to agricultural and environmental sustainability of Northeast China. This region is bread basket of China where the fertile and productive soils, Mollisols (also called Black soils), are primarily distributed. In this paper, we introduce the importance of Northeast China’s grain production to China, and describe the changes of sown acreage and grain production in past decades. This paper also summarizes the distribution, area and intensity of water erosion, changes in the number of gullies and gully density, thickness of top soil layer, soil organic matter content, bulk density, field water holding capacity, and infiltration rates; the number of soil microorganism and main enzyme activities from soil erosion in the region are also summarized. The moderately and severely water-eroded area accounted for 31.4% and 7.9% of the total, and annual declining rate is 1.8%. Erosion rate is 1.24–2.41 mm/year, and soil loss in 1°, 5° and 15° sloping farmlands is 3 t/ha/year, 78 t/ha/year and 220.5 t/ha/year, respectively. SOC content of uncultivated soil was nearly twice that of soil with a 50-year cultivation history, and the average annual declining rate of soil organic matter was 0.5%. Proper adoption of crop rotation can increase or maintain the quantity and quality of soil organic matter, and improve soil chemical and physical properties. Proposed strategies for erosion control, in particular how tillage management, terraces and strip cultivation, or soil amendments contribute to maintain or restore the productivity of severely eroded farmland, are discussed in the context of agricultural sustainability with an emphasis on the Chinese Mollisols.

Soil organic matter (SOM) is of primary importance for maintaining inherently low SOC contents (typically below 1%, Hunt soil productivity, and agricultural management practices may signifiet al., 1982). Consequently, small changes in the SOM cantly influence SOM chemical properties. However, how SOM chemical characteristics change with agricultural practices is poorly under-content are significant to the agricultural production of stood. Therefore, in this study, we evaluated the impacts of tillage the region. An evaluation of tillage and crop residue (conventional vs. conservation) management on the structural and management practices to rebuild SOC levels has been compositional characteristics of SOM using cross-polarization magicconducted by Hunt et al. (1996). These researchers monangle-spinning (CPMAS) and total sideband suppression (TOSS) itored changes in SOC levels in numerous small tillage solid-state 13 C nuclear magnetic resonance (NMR) and diffuse reflecplots and found that after 9 yr of CnT, the SOC content tance Fourier transform infrared (DRIFT) spectroscopy. We characin the top few centimeters was significantly higher than terized both physically and chemically isolated SOM fractions from a the soil under CT management. Campbell et al. (1999) Norfolk soil (fine-loamy, siliceous, thermic Typic Kandiudults) under reported that over an 11-to 12-yr period, increases in long-term tillage management (20 yr). The solid-state 13 C NMR results C storage in the 0-to 15-cm soil depth, because of indicated that humic acid (HA) from conventional tillage (CT, 0-5 cm) was less aliphatic and more aromatic than HA from conservation adoption of no-tillage, were small (0-3 Mg ha Ϫ1). Most tillage (CnT). The aliphatic C content decreased with increasing depth of the differences were observed in the 0-to 7.5-cm soil (0-15 cm) for both CT and CnT treatments. The reverse trend was depth, with little change in the 7.5 to 15 cm. However, true for aromatic C content. Based on reactive/recalcitrant (O/R) the short and long-term influences of disturbance on C peak ratio comparisons, HA was more reactive in the top soil (0-5 mineralization are complex and may vary depending cm) under CnT than CT. Both soil organic C (SOC) and light fraction on types of soil and plant residues (Hu et al., 1995; (LF) material were higher in the 0-to 5-cm soil of CnT than CT Franzleubbers and Arshad, 1996; Alvarez et al., 1998). treatment. Our results show that long-term tillage management can The strong influence of soil management on the amount significantly change the characteristics of both physical and chemical and quality of SOM was also reported by others (Janzen fractions of SOM.

In the three-dimensional extracellular matrix of the insect cuticle, horizontally aligned microfibrils composed of the polysaccharide chitin and associated proteins are stacked either parallel to each other or helicoidally. The underlying molecular mechanisms that implement differential chitin organization are largely unknown. To learn more about cuticle organization, we sought to study the role of chitin deacetylases (CDA) in this process. In the body cuticle of nymphs of the migratory locust Locusta migratoria, helicoidal chitin organization is changed to an organization with unidirectional microfibril orientation when LmCDA2 expression is knocked down by RNA interference. In addition, the LmCDA2-deficient cuticle is less compact suggesting that LmCDA2 is needed for chitin packaging. Animals with reduced LmCDA2 activity die at molting, underlining that correct chitin organization is essential for survival. Interestingly, we find that LmCDA2 localizes only to the initially produced chitin microfibrils that constitute the apical site of the chitin stack. Based on our data, we hypothesize that LmCDA2-mediated chitin deacetylation at the beginning of chitin production is a decisive reaction that triggers helicoidal arrangement of subsequently assembled chitin-protein microfibrils.