[Assessment of humic and fulvic acids in black soils using near-infrared reflectance spectroscopy].

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.

[Prediction of soil organic carbon in different soil fractions of black soils in Northeast China using near-infrared reflectance spectroscopy].

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.

[Effects of tillage mode on black soil's penetration resistance and bulk density].

Taking an eight-year field experiment site in Dehui County of Jilin Province, Northeast China as test object, this paper studied the effects of different tillage modes (no tillage and ploughing in autumn) on the penetration resistance and bulk density of black soil. No tillage increased the soil penetration resistance, especially at the soil depth of 2.5-17.5 cm. In the continuous cropping of maize and the rotation of maize-soybean, the maximum soil penetration resistance at planting zone under no tillage and ploughing in autumn was 2816 and 1931 kPa, and 2660 and 2051 kPa, respectively, which had no restriction on the crop growth. The curve of soil penetration resistance under ploughing in autumn changed with ridge shape, while that under no tillage changed less. Comparing with ploughing in autumn, no tillage increased the bulk density of 5-20 cm soil layer significantly. Under no tillage, the bulk density of 5-30 cm soil layer changed little, but under ploughing in autumn, soil bulk density increased gradually with increasing soil depth. There was no significant correlation between soil bulk density and soil penetration resistance.

[Field sampling methods for earthworm: a review].

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.

[Near infrared spectroscopy in determining organic carbon and total nitrogen in black soil of Northeast China].

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.