Ruqin Fan

Short-term effects of tillage practices on soil aggregate fractions in a Chinese Mollisol

Abstract Soil aggregate-size distribution and soil aggregate stability are used to characterize soil structure. Quantifying the changes of structural stability of soil is an important element in assessing soil and crop management practices. A 5-year tillage experiment consisting of no till (NT), moldboard plow (MP) and ridge tillage (RT), was used to study soil water-stable aggregate size distribution, aggregate stability and aggregate-associated soil organic carbon (SOC) at four soil depths (0–5, 5–10, 10–20 and 20–30 cm) of a clay loam soil in northeast China. Nonlinear fractal dimension (Dm) was used to characterize soil aggregate stability. No tillage led to a significantly greater aggregation for >1 mm aggregate and significant SOC changes in this fraction at 0–5 cm depth. There were significant positive relationships between SOC and >1 mm aggregate, SOC in each aggregate fraction, but there was no relationship between soil aggregate parameters (the proportion of soil aggregates, aggregate-associated SOC and soil stability) and soil bulk density. After 5 years, there was no difference in Dm of soil aggregate size distribution among tillage treatments, which suggested that Dm could not be used as an indicator to assess short-term effects of tillage practices on soil aggregation. In the short term, > 1 mm soil aggregate was a better indicator to characterize the impacts of tillage practices on quality of a Chinese Mollisol, particularly in the near-surface layer of the soil.

An appropriate time-window for measuring soil CO2 efflux: a case study on a Black soil in north-east China

Abstract Soil CO2 efflux rate is influenced by soil temperature which varies with time within a day. In order to determine a measuring time-window which can represent the daily average soil CO2 efflux rate from a Black soil in north-east China, soil CO2 efflux rates from no-tillage (NT) and mouldboard plough tillage (MP) plots were measured at a 2-h interval over 48 h four times in the growing season of 2008. Results showed that during the course of measurements, NT soil had a higher soil CO2 efflux rate than MP soil. Daily average soil CO2 efflux rate was matched relatively well with the CO2 efflux rate occurring between 09:00 h and 13:00 h, and between 19:00 h and 23:00 h. Our results indicate that the soil CO2 efflux rate measured between 09:00 and 11:00 h represents the daily average soil CO2 efflux rate during sunny days. When the measurements were conducted outside this time window, a procedure to adjust the CO2 efflux rates measured between 07:00 and 21:00 h (outside of the optimum time-window) to estimate daily average soil CO2 efflux rate is described.

Short-Term Impacts of No Tillage on Aggregate-Associated C in Black Soil of Northeast China

In order to get a good indicator to evaluate the impacts of no tillage (NT) on soil structure and soil quality, we studied the dynamics of total soil organic carbon (SOC) and aggregate-associated SOC, and their relationships in the plow layer (30 cm) in black soil of Northeast China under NT practice. The tillage experiment was established in Dehui County, Jilin Province, China, in 2001. The total SOC and aggregate-associated SOC under 5-yr tillage treatments were measured. NT practices did not lead to the increase of average SOC content at 0-30 cm depth, but it did significantly increase SOC at the top soil (0-5 cm). In NT plots, the change of SOC in >1 000 mu m aggregate was the same with that of total SOC, but the effect of NT on SOC in >1 000 mu m aggregate was greater than the effect on total SOC, suggesting that >1 000 mu m aggregate had more sensitive response to the impact of tillage practices. Also, significant positive correlation occurred between total SOC and SOC in >1 000 mu m aggregate in black soil. Consequently, in the short term soil macroaggregate >1 000 mu m could be used as an indicator to evaluate the impacts of tillage practices on soil structure in black soil of Northeast China.

Effects of tillage management on infiltration and preferential flow in a black soil, Northeast China

The impacts of no-tillage (NT) and moldboard plough (MP) managements on infiltration rate and preferential flow were characterized using a combined technique of double-ring device and dye tracer on a black soil (Mollisols) in Northeast China. The objective of this study is to evaluate how tillage practices enhance soil water infiltration and preferential flow in favor of soil erosion control in the study area. The steady infiltration rates under NT management are 1.6 and 2.1 times as high as those under MP management in the 6th and 8th years of the tillage management in place, while the infiltrated water amounts under NT management are 1.4 and 2.0 times as high as those under MP management, respectively. The depth of methylene blue penetrated into NT soil increases from 43 cm in the 6th year to 57 cm in the 8th year, which are 16 cm and 19 cm deeper than those in MP soil, respectively. The results of morphologic image show that more biological macro-pores occur in NT soil than in MP soil. These macro-pores play a key role in enhancing preferential flow in NT soil, which in turn promotes water infiltration through preferential pathways in NT soil. The results are helpful to policy-making in popularizing NT and have the implications for tillage management in regard to soil erosion control in black soil region of China.

Spatial variation of penetration resistance and water content as affected by tillage and crop rotation in a black soil in Northeast China

Limited information is available for understanding the spatial variation of soil penetration resistance (SPR) and water content induced by different tillage methods and crop rotations in a black soil of Northeast China. A 11-year tillage experiment in Dehui County, Jilin Province, Northeast China was conducted to evaluate the effects of tillage treatments [no tillage (NT), moldboard plow (MP), and ridge tillage (RT)] and crop rotations (corn-soybean rotation and continuous corn) on SPR and water content in relation to horizontal and vertical variations. Effect of NT, MP, and RT differed on the spatial distributions of SPR and water content among the rows, shoulders, and inter-rows. Compared with MP, NT, and RT treatments increased SPR in row and inter-row positions at the depth of 2.5–17.5 and 2.5–15 cm, respectively (p < 0.05). NT and RT led to significant decrement of soil water content than MP treatment in the rows and inter-rows of 0–15 cm layer (p < 0.05). Greater variability of SPR and water content was found in MP than NT and RT plots. Crop rotation did not have a marked impact on SPR and water content (p > 0.05). Tillage, sampling position, along with depth greatly affected SPR and water content (p < 0.05).

Curve-fitting techniques improve the mid-infrared analysis of soil organic carbon: a case study for Brookston clay loam particle-size fractions

Few studies have evaluated structural features of soil organic carbon (SOC) in different soil particle fractions, especially SOC changes induced by tillage, using Fourier transformed mid-infrared (MIR) spectroscopy. To make a contribution in this context, soil samples of a Brookston clay loam (mesic Typic Argiaquoll) with averaged pH and organic matter concentration at 7.28 and 43.9 g kg−1, respectively, were collected from short-term no-tillage (NT97) and mouldboard plow (CT97) treatments initiated in 1997 and long-term no-tillage (NT83) and mouldboard plow (CT83) treatments initiated in 1983 under a corn-soybean rotation, and were separated into sand, silt, and clay fractions using sonication. Structural features of SOC in these soil fractions were investigated using curve-fitting analysis of mid-infrared (MIR) spectra. Aromatic C content was found to be greater in clay- than in sand-sized fractions, while aliphatic C content was higher in sand- than in silt- and clay-sized particles. With decrease in tillage intensity, the aliphatic C gradually increased in sand- and clay-sized fractions but not in the silt-sized fraction. The aliphatic C content in sand fraction was significantly greater in NT83 than CT83 (P < 0.05). The aromatic C in silt- and clay-sized fractions was greater in NT83 than in both CT soils, whereas aromatic C contents were higher in both CT soils than in NT83 soil. Significantly higher aromatic/aliphatic C ratio in CT83 than NT83 was found in sand-sized fractions, while the opposite trend was found in the silt-sized fraction. These findings were not apparent until the curve-fitting technique was employed, which has the capacity to quantify many overlapped bands in the spectra. This study demonstrates that the curve-fitting of MIR spectra advances the analysis of organic matter in soil samples.