Xiaobing Liu

Soil Organic Carbon Dynamics in Black Soils of China Under Different Agricultural Management Systems

Cultivation can reduce soil organic carbon (SOC) content and lead to soil deterioration, but some agricultural management systems may increase SOC content and soil productivity. This research examined the SOC dynamics during a 50-year cultivation and how long-term agricultural management practices influenced SOC content in a typical black soil (Mollisol) region of P.R. China. The experiments selected four areas with different cultivation periods: uncultivated, five years, fourteen years, and fifty years. In addition, four long-term agricultural managements were initiated in 1992: conventional wheat–soybean rotation, wheat–sweet clover rotation, wheat–soybean rotation with addition of pig manure, and wheat–soybean rotation with addition of wheat straw. The SOC content declined rapidly at early years of cultivation and gradually afterwards. Wheat–soybean rotation with addition of wheat straw or pig manure resulted in a substantial increase in SOC content in 9 years. Thus, proper soil management can improve soil quality and health by increasing SOM content, and mitigate the greenhouse effect by sequestrating carbon dioxide from the atmosphere as indicated by the significant increase of organic carbon content in soil.

Fifteen years of research examining cultivation of continuous soybean in northeast China: A review

This paper reviews aspects of research on continuous soybean for the last 15 years in northeast China. Growth and development including changes of root nodule number and LAI are described, and reduction in yield and seed quality are discussed. The effects on physiological and biochemical processes, soil rhizosphere microbes, and soil properties are reviewed; and roles of root diseases, insect pests, and root exudates or plant residuals are discussed. Farm practices for alleviating effects on yield reduction are provided, and a diagram of the interaction among factors involved in continuous soybean yield reduction is presented.

Physical and Chemical Characteristics of a Typical Mollisol in China

Abstract Mollisols (called Black soils) in China are distributed primarily in the northeast region, which is one of the three largest Mollisol areas in the world. Black soils are of major agricultural importance in China. This study reports the physical and chemical properties of this soil with use of a typical Black soil profile selected in Heilongjiang Province, China, and standard soil analytical procedures. The soil is characterized with a thick (60 cm) mollic epipedon. The upper layer of the epipedon contains 5.8% organic carbon, and its CEC is 43.7 cmol(+)/kg. The macroaggregate (>0.25 mm) stability of the epipedon is high (between 63 and 68% of the soil sample weight), which provides favorable soil structure and conditions for plant growth. Soil texture is clay loam for all horizons except the upper layer of the mollic epipedon, which is sandy clay loam. Bulk density increases with depth, and total porosity declines with depth, due most likely to the profile distribution of organic carbon (decreasing with depth). Total nitrogen (N) and phosphorus (P) and available water are also larger in the upper epipedon than the lower horizons. Overall characteristics make this soil fertile and productive. The results of this study can be used as baseline data for examining any change in soil properties of the same soils resulting from agricultural management and practices and for comparisons of pedogenic and carbon cycling studies of Mollisols in China or worldwide.

Effects of Long‐Term Continuous Cropping, Tillage, and Fertilization on Soil Organic Carbon and Nitrogen of Black Soils in China

Abstract Cultivation and tillage practices alter soil properties and often lead to decline of soil quality. Adoption of appropriate agricultural management systems, however, may maintain soil productivity. This research examined the effects of long‐term continuous cropping, tillage, and fertilization on soil organic carbon (C) and nitrogen (N) contents of black soils in China. Soil samples from 11‐year tillage, 11‐year continuous cropping, and 16‐year fertilization experiments were analyzed. Soil organic carbon (SOC) and N declined with depth in all treatments. Compared with a wheat‐corn‐soybean rotation, continuous cropping of wheat, corn, or soybean reduced SOC and N contents, particularly SOC content. Continuous cropping of corn reduced SOC more than that of soybean or wheat in topsoil layers. Moldboard plowing significantly reduced SOC and N contents, whereas integrated tillage (i.e., moldboard plow for wheat, deep tillage (subsoiling) for soybean, and rotary tillage for corn) increased SOC and N relative to conventional tillage. Use of chemical fertilizers [N, phosphorus (P), and potassium (K)] along with return of crop residues resulted in a substantial increase in SOC and N in topsoil layers. It is proposed that the best management for maintaining soil productivity in the study area would be crop rotation along with the integrated tillage and addition of crop residues and chemical fertilizers.

Effect of soil type and soybean genotype on fungal community in soybean rhizosphere during reproductive growth stages

Fungal communities in soybean rhizosphere from reproductive growth stages R1 (beginning bloom) to R8 (full maturity) were studied based on the polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE) banding patterns of partial rDNA internal transcribed spacer regions (ITS1) and sequencing methods. Pot experiment subjecting three soybean genotypes grown in two soils (Mollisol and Alfisol) indicated that the soil type was the major factor in shaping the fungal communities in the soybean rhizosphere. Field experiment was conducted in an Alfisol field with three soybean genotypes, and both pot and field experiments showed that rhizosphere fungal communities shifted with growth stages, and more diversity of communities was found in early reproductive growth stages than later stages. No major difference among fungal communities of three soybean genotypes was detected at individual growth stage. BLAST search of ITS sequence data generated from excised DGGE bands showed that fungi belonging to Ascomycetes and Basidiomycetes predominantly inhabited in the soybean rhizosphere. In addition, a few bands had low similarity with database sequences inferred that unknown fungal groups existed in soybean rhizosphere.

Interaction between phosphorus nutrition and drought on grain yield, and assimilation of phosphorus and nitrogen in two soybean cultivars differing in protein concentration in grains.

ABSTRACT Drought affects many physiological and biochemical processes and thus reduces plant growth. Phosphorus (P) fertilization improves tolerance to drought stress in many plants. A greenhouse experiment examined the interactive effects of P nutrition and drought stress on P accumulation and translocation, yield, and protein concentration in grains of two cultivars of soybean [Glycine max (L.) Merr.]. Plants of cultivars ‘Heisheng 101’ (high protein in grains) and ‘Dongnong 464’ (low protein) were grown in a P-deficient soil supplied with 0–30 mg P kg−1 soil. Drought stress was imposed at the initial flowering (R1) or the podding (R4) stage. Drought stress limited P accumulation and reduced P translocation to the seed. The addition of P enhanced the concentration and accumulation of nitrogen (N) and P in shoots and seeds of both cultivars. Drought stress decreased shoot biomass, grain yield, and P accumulation; the decrease was greater in ‘Dongnong 46’ than ‘Heisheng 101,’ and even more so if drought stress was imposed at R4 than at R1. In contrast, drought stress increased the concentration of N in shoot and protein in grains. The addition of P alleviated the effect of drought stress on plant growth, P accumulation, and grain yield in both cultivars but to a greater extent in ‘Dongnong 46’. The results suggest that application of P fertilizers could mitigate drought stress at the reproductive stage, resulting in less yield penalty and improvement of grain quality of soybean grown in P-deficient soils.

Bacterial Community Structure in a Mollisol Under Long-Term Natural Restoration, Cropping, and Bare Fallow History Estimated by PCR-DGGE

Abstract Soil microbial biomass and community structures are commonly used as indicators for soil quality and fertility. A investigation was performed to study the effects of long-term natural restoration, cropping, and bare fallow managements on the soil microbial biomass and bacterial community structures in depths of 0–10, 20–30, and 40–50 cm in a black soil (Mollisol). Microbial biomass was estimated from chloroform fumigation-extraction, and bacterial community structures were determined by analysis of 16S rDNA using polymerase chain reaction-denaturing gradient gel electrophoresis (PCRDGGE). Experimental results showed that microbial biomass significantly declined with soil depth in the managements of restoration and cropping, but not in the bare fallow. DGGE profiles indicated that the band number in top 0–10 cm soils was less than that in depth of 20–30 or 40–50 cm. These suggested that the microbial population was high but the bacterial community structure was simple in the topsoil. Cluster and principle component analysis based on DGGE banding patterns showed that the bacterial community structure was affected by soil depth more primarily than by managements, and the succession of bacterial community as increase of soil depth has a similar tendency in the three managements. Fourteen predominating DGGE bands were excised and sequenced, in which 6 bands were identified as the taxa of Verrucomicrobia , 2 bands as Actinobacteria , 2 bands as α- Proteobacteria , and the other 4 bands as δ- Proteobacteria, Acidobacteria, Nitrospira , and unclassified bacteria. In addition, the sequences of 11 DGGE bands were closely related to uncultured bacteria. Thus, the bacterial community structure in black soil was stable, and the predominating bacterial groups were uncultured.

Phosphorus Application Affects the Soybean Root Response to Water Deficit at the Initial Flowering and Full Pod Stages

Application of phosphorus (P) fertilizer is an important factor for improving the tolerance to water deficit in many plants. A pot experiment was conducted to identify the effects of P application on soybean adaptability to water deficit at the R1 (initial flowering) and R4 (full pod) stages through the investigation of root morphological traits, plant P uptake and resultant yield in two soybean (Glycine max L. Merrill) cultivars (Dongnong 46 and Heisheng 101). The four levels of P application were 0, 7.3, 14.6 and 29.2 mg kg−2, respectively. The three water treatments were (1) 65–75% of field water capacity (FWC) as a well-watered control, (2) 30–40% of FWC at the R1 stage, and (3) 30–40% of FWC at the R4 stage. Root traits, plant uptake of P and yield were significantly reduced by water deficiency at different growth stages, especially at the R4 stage. Application of P enabled to alleviate the adverse effects of water deficit, to increase the root dry weight, root length and root surface area, and to slow root senescence after the R5 (initial pod filling) stage. The response of soybean genotypes to both water and P deficit was different. In the absence of P application, Dongnong 46 showed relatively low adaptability to water deficit at the R4 stage, whereas Heisheng 101 showed a lower reduction of root traits and yield. The beneficial effects of P application for Dongnong 46 were more pronounced than those for Heisheng 101. Based on this experiment, we suggested that P fertilizer application to soybean may be justified in low-rainfall years because of its ability to enhance the soybean adaptability to water deficit stress by improving the root morphology, P uptake and consequently yield.

Responses of photosynthetic rates and yield/quality of main crops to irrigation and manure application in the black soil area of Northeast China

Soil nutrients and water have long been recognized as the main determining factors influencing agricultural productivity in rain-fed agriculture. Manure application and irrigation can increase crop yield when nutrients and water are deficient. Often effects of water and nutrients are closely related and can not be easily separated in actual production. Three years of experiment were conducted in northern part of black soil area of Northeast China to investigate the responses of photosynthetic rates and yield/quality of main crops, wheat (Triticum aestivum L.), maize (May zeas L.), soybean (Glycine max L. Merr.) to irrigation and manure application. Irrigation and manure application had no effects on photosynthetic patterns during reproductive development in crops, maximum photosynthetic rates were achieved by irrigation, and manure application maintained relatively higher photosynthetic rates after the peak. On average, higher photosynthetic rates with irrigation may contribute to higher yield in soybean but not in maize and wheat. Responses of crop yield and quality to manure application and irrigation varied in the crops. Soybean yield and quality was very sensitive to irrigation and manure application. The greater supply of nutrients with sufficient water, the higher the yield. However, the high-yield of soybean achieved was accompanied with a decline of seed protein content. Maize yield mainly depended on nutrients used not the water supply, irrigation resulted in higher water content in the seed of maize and lower grain protein content in wheat at harvest, which is detrimental to seed storage in maize and processing quality in wheat. In the northern part of black soil area in Northeast China, the management of manure is critical to improve crop production, the optimum management for maize and wheat production was to apply chemical fertilizer and manure without irrigation, but for soybean was to apply fertilizer and manure with irrigation.

Methanogenic archaeal communities in paddy field soils in north-east China as evaluated by PCR-DGGE, sequencing and real-time PCR analyses

Abstract Community structures of methanogenic archaea in north-east China (NE China) were investigated by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE), sequencing and real-time PCR methods. Plow layer soil samples were collected from 15 paddy fields over a broad area in NE China during March and April 2007. The DGGE banding patterns of methanogenic archaeal 16S rRNA genes amplified with primers 1106F-GC and 1378R in NE China were distinctly different from those obtained from Anjo and Chikugo paddy fields in Japan, and were also influenced by soil types and sampling locations inNE China. Real-time PCR quantification showed that the numbers of methanogenic archaeal 16S rRNA genes and mcrA genes, encoding the methyl-coenzyme M reductase a subunit of methanogenic archaea, ranged from 4.0 × 106 to 2.7 × 108 and from 4.7 × 105 to 3.2 × 107 g−1 dry soil, respectively. In total, 53 DGGE bands were sequenced and 42 sequences with different nucleotides were detected; 85.7% of the sequences were identified as methanogenic archaea. Phylogenetic analysis of the sequenced 16S rRNA genes indicated that methanogenic archaea belonging to Methanosaetaceae, Methanocellales, Methanomicrobiales and Methanosarcinaceae dominated the paddy fields in NE China.