Xue-Ming Yang

The decomposed rate of crop residues is a major determinant for carbon balance and nutrient cycling in agroecosystem. In this study, a constant temperature incubation study was conducted to evaluate CO2 emission and microbial biomass based on four different parts of corn straw (roots, lower stem, upper stem and leaves) and two soils with different textures (sandy loam and clay loam) from the black soil region. The relationships between soil CO2 emission, microbial biomass and the ratio of carbon (C) to nitrogen (N) and lignin of corn residues were analyzed by the linear regression. Results showed that the production of CO2 was increased with the addition of different parts of corn straw to soil, with the value of priming effect (PE) ranged from 215. 53 µmol . g-1 to 335. 17 µmol . g -1. Except for corn leaves, the cumulative CO2 production and PE of clay loam soil were significantly higher than those in sandy loam soil. The correlation of PE with lignin/N was obviously more significant than that with lignin concentration, nitrogen concentration and C/N of corn residue. The addition of corn straw to soil increased the contents of MBC and MBN and decreased MBC/MBN, which suggested that more nitrogen rather than carbon was conserved in microbial community. The augmenter of microbial biomass in sandy loam soil was greater than that in clay loam soil, but the total dissolved nitrogen was lower. Our results indicated that the differences in CO2 emission with the addition of residues to soils were primarily ascribe to the different lignin/N ratio in different corn parts; and the corn residues added into the sandy loam soil could enhance carbon sequestration, microbial biomass and nitrogen holding ability relative to clay loam soil.

The organic carbon content and optical densities of humic acids in black soils of China were predicted and assessed using near infrared spectroscopy technique. The contents of humic acid (HA) and fulvic acid (FA) in 136 black soil samples in China were analyzed and the NIR spectra were collected using a VECTOR/22 (Fourier transform infrared spectroscopy). Partial least squares (PLS) regression with cross validation was used to develop prediction models with reference data and soil NIRS spectra, and the model was validated using an independent set of samples. NIRS well predicted (HAC+FAC), HAC and FAC contents, with R2 = 0.92, 0.92 and 0.86, RPD = 3.66, 3.82 and 2.69, and high correlation coefficients between predicted and measured values (r = 0.90, 0.85 and 0.82). Predictions for the E4 values of HA and FA were also good (R2 = 0.85, 0.85; RPD = 2.88, 2.65; r = 0.92, 0.80). Predictions for optical densities of HA and FA at 665 nm (E6) was acceptable. Generally, NIRS showed a good potential to predict C content and optical densities of humic acid and fulvic acid in blacks soils and may reveal information on SOC quality.

The soil organic carbon (SOC) associated with different soil fractions varies in the composition and dynamics. The present work is aimed to evaluate the potential of near infrared spectroscopy (NIRS) to predict SOC content in different soil fractions of black soils. SOC contents of 136 black soil samples in China were analyzed and the NIR spectra were collected using a VECTOR/22 (Fourier transform infrared spectroscopy). Partial least squares (PLS) regression with cross validation was used to develop calibrations between reference data and NIRS spectra (n = 100) which were validated using an independent set of samples (n = 36). Predictions for water-sieved aggregate associated organic carbon were generally good with R2 (coefficient of determination) ranging from 0.69 to 0.82 and the RPD (residual prediction deviation) from 1.2 to 1.8. NIRS well predicted the SOC in < 53 microm mineral fraction (R2 = 0.97, RPD = 5.4), but the prediction for SOC in 250-2 000 microm or in 53-250 microm particulate matter fractions was poor. However, the prediction for the SOC in 53-2 000 microm fraction was good (R2 = 0.79, RPD = 2.2). In addition, NIRS very well predicted the SOC in fine particle fraction (< 20 microm) (R2 = 0.93, RPD = 3.8). Accordingly, NIRS showed a good potential to predict SOC in some soil fractions and could reduce tedious laboratory analysis.

As a critical component of soil ecosystem, earthworm can improve soil structure and relates closely to soil nutrient cycling, playing an important role in promoting soil quality and productivity. However, there is lack of systematic study on the field sampling methods for earthworm, especially in China. This paper reviewed the operational processes of commonly used field sampling methods for earthworm, and discussed their corresponding merits, efficacy, and potential influence on research results. To achieve a complete and accurate characterization of earthworm community size and structure, the method of chemical repellent combined with hand-sorting could work well at the sites where physical disturbance was acceptable, while the AITC (allyl isothiocyanate) method would be a favorable option at the sites where soil destruction was not feasible.

In this study, near infrared reflectance spectroscopy (NIRS) was used to determine the organic carbon (OC), total nitrogen (TN), and C/N ratio in black soil of Northeast China. Based on the 3699-12000 cm(-1) NIRS of 136 black soil samples collected in 2004-2005, and by using partial least square (PLS), the related quantitative models were established. Leave-one-out cross validation showed that the OC and TN were well predicted, with the values of coefficient of determination (R2) being 0.92 and 0.91, RPD (the ratio of standard deviation of validation set to root mean square error of cross validation) being 3.45 and 3.36, and correlation coefficient (r) being 0.94 and 0.93 respectively, suggesting that NIRS had the potential to predict the OC and TN in black soil of Northeastern China. However, the C/N ratio was poorly predicted, with R2 = 0.61, RPD = 1.61, and r = 0.74, indicating that NIRS could not give reasonable prediction for the C/N ratio in black soil.

By using dye tracer and double-ring infiltrometer techniques, the characters of infiltration and preferential flow of black soil under no-tillage (NT) and fall moldboard plow (MP) were compared after six years continuous management. The results showed that the infiltration rate was higher under NT than under MP. When the infiltration reached steady, the infiltration rate and accumulative infiltration capacity under NT were 1.35 and 1.44 times as high as those under MP, respectively. The penetration depth of methylene blue reached a depth of 43 cm in NT soil, being 16 cm deeper than that in MP soil. Comparing with MP soil, NT soil had better development of pore structure and more biological pores, and presented better preferential flow character, which were of importance for water infiltration and soil and water conservation.

The study on the distribution characters of water-stable aggregates and aggregate-associated C in 32 pairs of virgin and cultivated black soils in Northeast China showed that in virgin soils, the amount of water-stable macroaggregates (>0.25 mm) and their associated C in 0-30 cm layer were higher than those of microaggreagtes (< 0.25 mm). With the increase of soil depth, the amount of macroaggregates and their associated C showed a decreasing trend, while those of microaggregates increased significantly (P < 0.01). The distribution characters of aggregates in cultivated soils were in adverse to virgin soils. Compared with those in virgin soils, the amount of macroaggregates and their associated C in 0-30 cm layer in cultivated soils declined drastically, particularly for >1 mm aggregates. In virgin soils, the proportions of soil macroaggregates, especially for >1 mm aggregates, were positively correlated to soil organic carbon; but in cultivated soils, no obvious relationship was observed between them. The associated C of soil aggregates was positively correlated to soil total organic carbon in both virgin and cultivated soils (P <0.01). In cultivated soils, less C was associated with macroaggregates but 37% more C was associated with microaggreagtes, and the total soil organic carbon was decreased by 29.5%, in comparison with those in virgin soils, which suggested that soil macroaggregates played an important role in the dynamics changes of soil total organic carbon. It was indicated that soil water-stable macroaggregates were sensitive to soil management, and could be an indicator in evaluating the impacts of agronomic managements on soil fertility and soil quality.

A long‐term fertilization experiment with monoculture corn (Zea mays L.) was established in 1980 on a clay‐loam soil (Black Soil in Chinese Soil Classification and Typic Halpudoll in USDA Soil Taxonomy) at Gongzhuling, Jilin Province, China. The experiment aimed to study the sustainability of grain‐corn production on this soil type with eight different nitrogen (N)‐, phosphorus (P)‐, and potassium (K)–mineral fertilizer combinations and three levels (0, 30, and 60 Mg ha^–1 y^–1) of farmyard manure (FYM). On average, FYM additions produced higher grain yields (7.78 and 8.03 Mg ha^–1) compared to the FYM0 (no farmyard application) treatments (5.67 Mg ha^–1). The application of N fertilizer (solely or in various combinations with P and K) in the FYM0 treatment resulted in substantial grain‐yield increases compared to the FYM0 control treatment (3.56 Mg ha^–1). However, the use of NP or NK did not yield in any significant additional effect on the corn yield compared to the use of N alone. The treatments involving P, K, and PK fertilizers resulted in an average 24% increase in yield over the FYM0 control. Over all FYM treatments, the effect of fertilization on corn yield was NPK > NP = NK = N > PK = P > K = control. Farmyard‐manure additions for 25 y increased soil organic‐matter (SOM) content by 3.8 g kg^–1 (13.6%) in the FYM1 treatments and by 7.8 g kg^–1 (27.8%) in the FYM2 treatments, compared to a 3.2 g kg^–1 decrease (11.4%) in the FYM0 treatments. Overall, the results suggest that mineral fertilizers can maintain high yields, but a combination of mineral fertilizers plus farmyard manure are needed to enhance soil organic‐matter levels in this soil type.