Abstract:Soil compaction by agricultural machinery has become one of the most serious soil degradation problems in the world. This paper reviewed the research progress of soil compaction from four aspects: detection, impact, alleviation and prevention of soil compaction. It shows that new detecting methods are urgently needed for field soil compaction detection. The impact of soil compaction is mostly focused on the top cultivated soil layer, but the effects of subsoil compaction and its potential ecological services in addressing climate change have been overlooked. Reasonable agricultural management strategies such as crop and tillage rotation methods could be applied to alleviate soil compaction. Overall, subsoil compaction is difficult to alleviate in a short period and prevention should be the top priority although there is still a lack of practical prevention methods. Agricultural mechanization in China is still in the early development stage, and effective preventive measures should be taken to avoid soil compaction like that in developed countries.

Abstract:[Objective] In order to improve soil structure of the subsoil layer of black soil and solve the problem of how to return maize straw in Northeast China, a three-year (2015—2018) field experiment was carried out.[Method] The field experiment was designed to have three treatments in returning pattern, i.e. CK (no straw return), QS (returning of chopped straw) and KL (returning of pelletized straw), and three treatments in straw returning dosage, i.e. low dosage (15 000 kg·hm-2), medium dosage (45 000 kg·hm-2, 3 times as much as the low dosage) and high dosage (75000 kg·hm-2, 5 times as much as the low dosage), and all had the straw buried in the soil 30-40 cm depth. Effects of the treatments on soil bulk density, soil compactness and soil water content were explored, and effects of soil aggregate distribution regulating soil physical properties was analyzed.[Result] The tests of the soil samples collected at the maize maturity stage of the three year experiment show:1) The practice of deep straw returning reduced soil bulk density and soil compactness and increased soil water content, and the effects were more significant in the 20-40 cm layer than in the 0-20cm soil layer. Moreover, the effects become more significant with increasing of straw dosage, and less with the time going on, and the effects of straw returning once at a high rate might last for a few years. In the third year of the experiment, only QS5 reduced soil bulk density significantly or by 10.9% (P < 0.05), and QS5 and KL5 lowered soil compactness by 24.1% and 22.0% (P < 0.05), but raised soil water content by 8.9% and 7.4% (P < 0.05), respectively; 2) The treatments of medium and high in dosage significantly increased the content of macroaggregates and reduced the content of microaggregates in the subsoil, and the fractions of > 0.25 mm water stable aggregates and of the > 2 mm large aggregates increased significantly with rising straw dosage. Whats more, the return of pelletized straw tended to promote the formation of macroaggregates than the return of chopped straw. The first and second years of straw returning were the main period for formation of macroaggregates, of which the highest content reached up to about 5 times and 1.5 times than that in CK, respectively; 3) Significant relationships were observed of 0.25-0.053 mm micro aggregate and > 0.25 mm water stable aggregate with soil bulk density, soil compactness and soil water content in the subsoil layer (P < 0.05), and the 0.25-0.053 mm, > 2 mm, and > 0.25 mm fractions of aggregates were the key factor driving changes in soil physical properties in 2016 and 2017, but the 1-0.5 mm fraction of aggregates was found to be the key factor driving the changes in soil physical properties in 2018.[Conclusion] Therefore, from the perspective of recycling maize straw in Northeast China, the return of chopped straw with a rate of 75 000 kg·hm-2 is a good management to regulate the distribution of soil aggregates and improve the physical properties of subsoil. The finding may provide a theoretical basis and technical guidance for improvement of soil structure of the black soil in China.

Abstract:【Objective】It is of great scientific significance to explore effects of the practice of subsoiling coupled with fertilization on the fractions of activated organic carbon and nitrogen, and enzyme activities in black soil. 【Method】Based on a 2-year field experiment in Qinggang County, Heilongjiang Province, a black soil region typical of Northeast China, variations of the soil were analyzed in fractions of dissolved organic carbon (DOC), microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), particulate organic carbon (POC), particulate organic nitrogen (PON), and readily oxidizable organic carbon (ROC), and in activity of N-acetylglucosaminnidase (NAG), Cellobiohydrolase (CBH), β-glucosidase (BG) and β-xylosidase (BXYL) with treatment in the experiment, which consisted of five treatments, including no-till + chemical fertilizer (T1), subsoiling 25 cm (in depth) + chemical fertilizer (T2), subsoiling 25 cm + chemical fertilizer + organic manure (T3), subsoiling 35 cm + chemical fertilizer (T4), sub-soiling 35 cm + chemical fertilizer+ organic manure (T5) .【Result】Results showed that both subsoiling and fertilization and their interactions significantly affected the contents of soil activated carbon and nitrogen, particularly of POC and PON; Subsoiling (T2 and T4) significantly reduced the contents of soil activated organic carbon and nitrogen components with varying degree relative to depth of subsoiling, T2 was significantly lower than T1 (P<0.05) in POC and PON content; T3 and T5 significantly increased the contents of soil activated organic carbon and nitrogen. T3 was 8.37%, 46.64%, 35.10% and 42.39% (P<0.05) higher than T2 in content of SOC, POC, ROC and PON. Besides, subsoiling improved stability of the soil activated organic carbon and nitrogen components. Compared with T1, subsoiling treatments significantly reduced the ratios of MBC/SOC and POC/SOC in the soil (P<0.05), and subsoiling 35 cm in depth significantly decreased the ratio of PON/TN (P<0.05); T2 and T4 did not differed much from T1 in enzyme activity, whereas T3 significantly increased CBH activity relative to T2. 【Conclusion】To sum up, subsoiling 25 cm in depth combined with application of chemical fertilizer and organic manure can maintain the content of activated organic carbon and nitrogen components in the soil, hence it is recommended to be extrapolate as an effective farming technique to build up black soil farmland and to increase organic matter content in the soil of this area.

Abstract:【Objective】Red soil slope farmlands are an important cultivated land resource in South China. Because of long-term unreasonable tillage measures and uneven spatial and temporal distribution of precipitation, resultant serious soil erosion on slope farmlands in this area has led to a sharply declining productivity and low and unstable crop yields, thus seriously restricting development of the agriculture in South China. Reasonable tillage measures play an important role in improving soil structure, increasing water use efficiency, preventing soil erosion, improving ecological environment, building up land productivity and raising crop yields. In this paper, a tract of red soil slope farmland in Yunnan Province was taken as research object. Farmlands under different tillage measures were compared in soil quality. This study was conducted to explore mechanisms of tillage measures affecting erosion resistance and production performance of the cultivated-layers of the farmlands, in an attempt to provide certain scientific basis for quality evaluation of the cultivated-layers of red soil slope farmlands and improvement of conservative tillage technologies for red soil slope farmlands.【Method】In this study a total of 15 experimental plots were set up and cultivated for comparison between different tillage measures or treatments, i.e. CK (traditional tillage), NT (no-tillage), P20 (tillage 20 cm in depth), P20C (tillage 20 cm in depth + compaction), and P20S30 (tillage 20 cm + subsoiling 30 cm in depth), in soil quality of the cultivated layer, and one-way ANOVA and soil quality index method were used to analyze the experimental data.【Result】Results show:（1）The impacts of tillages on erosion resistance of the cultivated-layers in red soil slope farmlands. Compared with Treatment CK, Treatment P20S30 increased by 28.13% in average mass diameter of water-stable aggregates. Treatment NT was the highest in shear strength (12.12 kg·cm-2), and in soil saturated hydraulic conductivity (1.27 mm·min-1) as well. Treatment P20 was the highest in content of >0.25 mm water-stable aggregates, in mean weight diameter of water-stable aggregates and in geometric mean diameter of the aggregates, reaching up to 69.64%, 1.74 mm and 0.77 mm, respectively;（2）The impact of tillage on productivity of the cultivated-layer in red soil sloping farmland varied with treatment. In Treatment NT, soil bulk density significantly increased, and soil organic matter and available phosphorus concentrated in the surface layer. In Treatment P20 and P20S30, the cultivated-layer was significantly thicker, and the soil organic matter and available phosphorus contents increased significantly;（3）And the effect of tillage on soil quality of the cultivated-layer and on the suitability of the diagnostic indices varied with treatment. Treatment P20S30 was the highest in soil quality index (0.58); and Treatments P20 and P20S30 varied within the range of suitability in thickness, bulk density and available phosphorus index of the cultivated-layer. Treatment P20 was the highest in organic matter content.【Conclusion】All the findings in this study may serve as reference for selection of suitable tillage measures, and evaluation and construction of a rational cultivated-layer in red soil slope farmlands.

Abstract:【Objective】To solve the problems of soil organic carbon deficiency in the subsoil layer and the yield of crop straw being too large in volume to make full use of in farmlands of black soil in Northeast China, a long-term (2015—2018) field experiment was carried out. 【Method】The field experiment was designed to have three treatments, i.e. CK (no straw returned), FS (returning of chopped straw) and KL (returning of pelletized straw), and three straw returning rates, i.e. Rate 1 (15 t•hm-2), Rate 2 (45 t•hm-2, 3 times as high as Rate 1) and 3 (75 t•hm-2, 5 times as high as Rate 1). The straw was deeply incorporated into the subsoil layer. Soil samples were collected from all the plots separately each year for analysis of soil organic carbon content, organic carbon structure and soil nutrient ratio in an attempt to find out a way to turn waste into treasure and hence to promote sustainable development of black soil. 【Result】Results show: 1. Organic carbon content in the subsoil of the treatment plots varied in the range of 2%-20%(1 a), 5%-27%(2 a) and 1%-18%(3 a). The effect of straw returning raising organic carbon content in the subsoil was significant and improved with increasing returning rate and the effect of the treatments the highest in returning rate were the most significant and particularly in the second year, which indicates that organic carbon accumulation occurred mainly in the second year. Two-way variance analysis shows that straw returning rate was an important factor affecting soil organic carbon; 2. Nuclear magnetic resonance test shows that at the end of the experiment, the organic carbon in Treatment FS5 was found the highest in aliphaticity, while that in Treatment KL5 the highest in aromaticity, indicating that chopped straw is more likely to promote formation of organic carbon of alkyl carbon chain, while pelletized straw is to promote formation of organic carbon of aromatic hydrocarbon type; 3. In Treatments FS5 and KL5, soil C/N and C/P ratios increased by >10%, and C/K ratio did by >20%. The effect in Treatments KL was short and instant, while that in Treatments FS was long and slow. 【Conclusion】In a conclusion, deep incorporation of processed straw at a high rate can significantly increase organic carbon in the subsoil layer and help keep soil carbon in balance with nitrogen, phosphorus and potassium. It is, therefore, a feasible way to build up the black soil in thickness and fertility and to solve the difficult problem of straw returning in Northeast China.