Xinhua Peng

Influence of types of restorative vegetation on the wetting properties of aggregates in a severely degraded clayey ultisol in subtropical China

Vegetation may affect soil physical behaviour because of increases in hydrophobic organic compounds that bind soil particles and reduce the rate of wetting by inducing a low level of water repellency. These processes have not been isolated previously, so the aim of this study was to evaluate how different types of restorative vegetation influence the water repellency and pore structure of soil. We measured an index of water repellency, R, as the ratio between water and ethanol sorptivities on the surfaces of different size soil aggregates from a severely degraded clayey Ultisol. R is proportional to the decrease in water sorptivity. The treatments were (1) eroded bare land, two types of restorative vegetation—(2) deciduous Camphor trees (Cinnamomum camphora) and (3) leguminous Lespedeza shrubs (Lespedeza bicolor), (4) Masson pine (Pinus massoniana), and (5) a vegetable garden with large annual inputs of pig manure. R increased from <1.5 in eroded bare land up to the range from 2.0 to 4.4 when this land was planted with vegetation. Undisturbed soil under Masson Pine had an Rg3. Large (20–50 mm) aggregates had greater water repellency and porosity than small (10–20 mm) aggregates, particularly under Camphor trees. The type of vegetation and pore structure therefore affects water repellency. Isolating these properties will help us understand how plant selection and soil management influence soil physical behaviour and structure dynamics. D 2003 Elsevier Science B.V. All rights reserved.

Effect of Biochar Addition on Maize Growth and Nitrogen Use Efficiency in Acidic Red Soils

Biochar added to soil can improve crop growth through both direct and indirect effects, particularly in acidic, highly weathered soils in subtropical and tropical regions. However, the mechanisms of biochar improving crop growth are not well understood. The objectives of this study were i) to determine the crop responses to biochar addition and ii) to understand the effect of biochar addition on N use efficiency. Seven acidic red soils varying in texture, pH, and soil nutrient were taken from southern China and subjected to four treatments: zero biochar and fertilizer as a control (CK), 10 g kg−4 biochar (BC), NPK fertilizers (NPK), and 10 g kg−1 biochar plus NPK fertilizers (BC+NPK). 15N-labeled fertilizer was used as a tracer to assess N use efficiency. After a 46-d pot experiment, biochar addition increased soil pH and available P, and decreased soil exchangable Al3+, but did not impact soil availabe N and cation exchange capacity (P > 0.05). The N use efficiency and N retained in the soil were not significantly affected by biochar application except for the soil with the lowest available P (3.81 mg kg−1) and highest exchanageable Al3+ (4.54 cmol kg−1). Greater maize biomass was observed in all soils amended with biochar compared to soils without biochar (BC vs. CK, BC+NPK vs. NPK). This agronomic effect was negatively related to the concentration of soil exchangeable Al3+ (P < 0.1). The results of this study implied that the liming effect of biochar improved plant growth through alleviating Al toxicity and P deficiency, especially in poor acidic red soils.

Influence of soil structure on the shrinkage behaviour of a soil irrigated with saline–sodic water

Soil structural properties of swelling/shrinking soils play an important role in assessing hydraulic properties. However, the effect of shrinkage/swelling processes on structure formation and strength especially in saline–sodic soils, such as a Typic Chromexert, has not yet been clarified. In this study, we investigate the changes in the shrinkage pattern after applying saline sewage water and use a 3-parameter sigmoidal curve model to fit its shrinkage data. Our aims were to determine the overall effect of sewage water application on soil structure and shrinkage processes after applying saline–sodic water and to evaluate soil shrinkage behaviour through parameters in relation to soil properties. Three plots within the FILTER Project, which were irrigated for summer and winter irrigated cropping with around 1000 m3/ha every 2 weeks with different saline sewage effluent concentrations for >5 years, were sampled from the top horizon to 1.00 m depth. The exchangeable sodium percentage is greatly decreased due to the application of low salt concentration except in the deep horizon. Soil structural properties such as aggregate strength and hydraulic properties are improved, especially in topsoil horizon. The stabilised soil structure reduces the volume change of structural shrinkage. Three parameters of the shrinkage model, defined as α, m, and n, present different physical meanings in relation to soil structure. Parameters α and m have similar functions, both a significantly exponential relationship with aggregate strength and a linear relationship with structural and residual shrinkages, whereas parameter n has a significantly linear relationship with aggregate strength and with the slope of the proportional shrinkage. The relation between parameters of the model and shrinkage behaviour facilitates the prediction of changes in pore water and soil structure and will be a useful tool for modelling water flow in non-rigid soils.

EFECTO DEL CAMBIO DE USO EN LA ESTABILIDAD DE LA ESTRUCTURA Y LA FUNCIÓN DE LOS POROS DE UN ANDISOL (TYPIC HAPLUDAND) DEL SUR DE CHILE

Los suelos volcanicos del sur de Chile constituyen cerca del 60% del suelo arable del pais. Estos suelos se encuentran bajo un amplio rango de usos desde sistemas pristinos hasta otros con un uso intensivo. El objetivo de este trabajo fue determinar el efecto del cambio de uso de suelo sobre: i) la estabilidad del suelo frente a presiones externas e internas; ii) la conductividad hidraulica y iii) su resiliencia funcional. Muestras disturbadas y no disturbadas de suelo fueron recolectadas a 5, 20, 40 cm de profundidad en un suelo Andisol (Typic Hapludand) bajo un renoval de bosque nativo (NF), una pradera de 50 anos (P50) y otra de 1 ano de uso (Pl). Se determino la curva de retencion de agua, contraccion y consolidacion, la conductividad hidraulica saturada (Ks), permeabilidad de aire (Ka), contenidos de carbono organico (CO), textura y alofan. Se estimo la conductividad hidraulica no saturada (Ku) de acuerdo al modelo propuesto por van Genuchten (1980). Se definieron indices de deformacion de suelo como consecuencia de estreses mecanicos (COELm) e hidraulicos (COELh). El suelo estudiado esta sujeto a constantes cambios en su estructura como consecuencia de estreses mecanicos e hidraulicos afectando la distribucion de los poros y su funcionalidad. La magnitud de estos cambios disminuye con el incremento de la intensidad de uso del suelo. La gran capacidad de contraccion del suelo puede traer consecuencias en su comportamiento hidraulico dependiendo de la intensidad del secado a traves de la formacion de grietas y vias de flujo de preferencial. Finalmente, los poros del suelo son capaces de recuperar su integridad funcional despues de una compactacion, lo que esta estrechamente relacionado con los contenidos de materia organica.

Effects of Grazing Intensity on Soil Water Regime and Flux in Inner Mongolia Grassland,China

Abstract In the past few decades, the increase in grazing intensity has led to soil degradation and desertification in Inner Mongolia grassland, China, due to population growth and shift in the socio-economic system. Two sites with different grazing intensities, continuous grazing site (CG) with 1.2 sheep ha−1 year−1 and heavy grazing site (HG) with 2.0 sheep ha−1 year−1, were investigated at the Inner Mongolia Grassland Ecosystem Research Station (43° 37′ 50″ N, 116° 42′ 18″ E) situated in the northern China to i) characterize the temporal distribution of soil water content along soil profile; and ii) quantify the water fluxes as affected by grazing intensity. Soil water content was monitored by time domain reflectometry (TDR) probes. Soil water retention curves were determined by pressure membrane extractor, furthermore processed by RETC (RETention Curve) software. Soil matric potential, plant available water and water flux were calculated using these data. Both sites showed an identical seasonal soil water dynamics within four defined hydraulic periods: 1) wetting transition coincided with a dramatic water increase due to snow and frozen soil thawing from March to April; 2) wet summer, rainfall in accordance with plant growth from May to September; 3) drying transition, a decrease of soil water from October to November due to rainfall limit; and 4) dry winter, freezing from December to next February. Heavy grazing largely reduced soil water content by 43%–48% and plant available water by 46%–61% as compared to the CG site. During growing season net water flux was nearly similar between HG (242 mm) and CG (223 mm) sites between 5 and 20 cm depths. However, between 20 and 40 cm depths, the upward flux was more pronounced at HG site than at CG site, indicating that water was depleted by root uptake at HG site but stored at CG site. In semi-arid grassland ecosystem, grazing intensity can affect soil water regime and flux, particularly in the growing season.

Contrasted effects of biochar on maize growth and N use efficiency depending on soil conditions

Abstract Biochar amendment may improve crop growth through its nutrients and indirect fertility. However, this improvement varies in a wide range of biochars, crops, and soils. Our objectives were to determine the response of crop growth to biochar amendment and to assess the N use efficiency relative to the biochar and the soil types. In this pot experiment, we investigated five typical agricultural soils in China amended with two biochars. Four treatments were designed: the soil itself as a control, the soil amended with 1% biochar, the soil with fertilizer NPK, and the soil with added biochar and fertilizer. Biochar amendment increased the maize biomass and the N use efficiency in the red soil (p<0.05) but not in the other four soils (p>0.05). In the red soil, the biomass under biochar+NPK was 2.67-3.49 times higher than that of only NPK, and 1.48-1.62 times higher than that of only biochar amendment, 21-36 and 35-42% of which were contributed from biochar fertility and indirect fertility, respectively. This study indicates that biochar amendment is very plausible for the red soil but has a minor or even negative effect on the other four soils in China.

Sorption and Leaching Potential of Isoproturon and Atrazine in Low Organic Carbon Soil of Pakistan Under a Wheat-Maize Rotation

Abstract Pesticide leaching is a great threat in low organic carbon soils when subjected to improper irrigation scheduling. Limited data are available on the sorption and leaching potential of pesticides in agricultural soils of Pakistan with low soil organic carbon (SOC). Lysimeter and field studies were conducted with and without manure application at two irrigation levels in a wheat-fallow-maize rotation in Faisalabad, Punjab, Pakistan. Isoproturon was applied to wheat 55 d after sowing at 1 kg active ingredient (a.i.) ha−1, while atrazine was sprayed on maize 30 d after sowing at 0.774 kg a.i. ha−1. Soil was sampled from three depths (0–35, 35–70, and 70–110 cm) for the field study and four depths (0–35, 35–70, 70–115, and 115–160 cm) for the lysimeter study, 280 and 65 d after application of isoproturon and atrazine, respectively. The soil-water partition coefficients (Kd) of isoproturon and atrazine ranged from 0.3 to 1.2 and 0.4 to 1.5 L kg−1, respectively, and increased linearly with increase in SOC contents. The organic carbon-normalized soil-water partition coefficient (Koc) of isoproturon and atrazine averaged 246.1 and 184.9 L kg−1, respectively, being higher with low spiking concentration. Isoproturon residues measured 280 d after application ranged from 2.1% to 3.6% of the applied mass in the lysimeter study and from 1.5% to 3.1% under field conditions. Atrazine residues 65 d after application ranged from only 0.62% to 0.78% and from 0.88% to 0.82% in the lysimeter and field studies, respectively. The lowest levels of residues for both pesticides were observed with frequent irrigation applied to manure-amended soil. A pesticide leaching risk screening tool, the ground water ubiquity score (GUS), indicated that in the absence of manure under both irrigation levels, isoproturon has a leaching potential (GUS = 2.8), while with the application of manure it has a very low leaching risk. Atrazine GUS ranged from 1.7 to 1.9, indicating a very low risk of leaching.

Modeling Grazing Effects on Soil-Water Budget Under Leymus chinensis and Stipa grandis Vegetation in Inner Mongolia, China

Abstract To better understand the effects of different grazing intensities on soil-water dynamics and its budget in Inner Mongalia, China, five sites, under two representative vegetation types, Leymus chinensis (LC) and Stipa grandis (SG), were investigated: ungrazed sites since 1979, LCUG79 and SGUG79, a winter grazed site (LCWG), a continuously grazed site (SGCG) defined as a moderate grazing intensity, and a heavily grazed site (LCHG). Soil, plant, and meteorological data were collected for use in modeling soil-water content and its budget during growing seasons from 2008 to 2009 using the HYDRUS-1D. The soil-water content in 2010 was simulated using annually averaged values of initial and boundary conditions. Our results showed that grazing reduced total pores and saturated hydraulic conductivity but ungrazed sites benefited from natural recovery. Greater transpiration was observed at the SGCG site when compared with the LCWG and LCHG sites. At the two ungrazed sites, transpiration was greater in the SG region as compared with the LC region. Rainfall reduced the difference between potential and actual evapotranspiration through increasing plant-available water. The simulation of soil water in 2010 using annually averaged parameters was determined to be an acceptable alternative to actual on-site observation. Our data suggest that selection of an appropriate grazing intensity may be possible via simulation modeling for use in making land management decision, especially in the absence of on-site observations as often is the case from such remote regions.