Abstract:Three types of Point of Zero Charge (PZC), i. e. ck-PZC (Without B), ads-PZC(B adsorp tion) and des-PZC(B desorption), were measured in brown-red soil, yellow-brown soil and calcareous alluvial soil collected from Hubei Province. The ads-PZC, compared with its ck-PZC, decreased by 0.9 pH unit for the brown-red soil, and only by 0.3 pH unit for the yellow brown soil, but the corresponding adsorbed H⁺ (the potential ion) increased by 3.3 cmol kg^-1 and 3.5 cmol kg^-1, respectively. Therefore, if specific adsorption of B occurred, the buffering capacity of the yellow-brown soil for environmental acid was higher than that of the brown-red soil. The ads-PZC of the calcareous alluvial soil was nearly equal to its ck-PZC, and its adsorbed H⁺ varied within 1.0 cmol kg^-1. Most of the potential ion in electrolyte did not react with surface funct ional groups of soil colloid, but with calcium carbonate. Though the change in des-PZC to ads-PZC was small, the calcareous alluvial soil retained strong trend to adsorb H⁺ at B desorption. The amount of adsorbed H⁺ was two folds as much as that in the brown-red soil or the yellow brown soil, which suggested that the accelerat ing effect of adsorbed B on H⁺ adsorption by the calcareous alluvial soil just appeared at that time. The amount of B adsorbed changed with pH variation, which is connected with surface characteristics of soil colloids and B types. In lower pH range, net negative charge of soil surface was small, but B could combine with positiveion as ion pair, which was adsorbed on soil surface. The result also showed that the adsorption of B caused a ten fold increase of the adsorption of proton in acid soils.

Abstract:A ¹⁴C-labelling technique was used to study turnover of microbial biomass C of 3 red soils with different texture, i. e., vegetable garden of red sandy soil, citrus orchard and tea garden of clayey soil, for which the turnover periods of soil microbial biomass C were 80 days, 139 days and 170 days, respectively. The turnover period was closely related to clay content, and longer in the red sandy soil than in the clayey soils, suggesting that organic matter can be faster decomposed and transformed by microorganisms and nutrients more easily released in the sandy soil, in other words, nutrients may be retained longer in clayey soil. However their turnover period was little affected by land use form, pH and organic matter content. In general, the turnover period for red soils was shorter than that reported for other types of soils, which shows that quicker turnover of organic matter and nutrients went on in acidic red soils of the tropical-subtropical regions and this may be one of the reasons for nutrient deficiency in red soils. To study the turnover of microbial biomass C is quite significant in evaluating and managing red soil fertility.

Abstract:The adsorption of chloride ions by three variable charge soils and four constant charge soils of China were determined in different concentrations of co-existing SO₄^2- and accompanying Na⁺, K⁺, NHNH₄⁺, Mg²⁺, Ba²⁺ and Al^₃+, respect ively. The results indicated that the amount of Cl^- adsorbed by soils in different electrolyte solutions decreased in the order AlCl₃ > BaCl₂ and MgCl₂ > KCl and NH₄Cl> NaCl. However, the difference of Cl^- adsorption among electrolyte solutions was more significant in variable charge soils. In the same electrolyte solution, the amount of Cl^- adsorbed by different soils decreased in the order latersol> red earth> red latersol> yellow brown earth> brown earth, dark brown earth and black soil, which agreed with the order of posit ive surface charge of these soils. For variable charge soils, within the range of 0.5 to 5 mmol L^-1 of Cl^- added, the adsorption can be described by the Langmuir equation sat isfactorily, and the adsorpt ion energy parameter (K) calculated from the equation was similar in magnitude when different cations co-existed. The pH of the equilibrium solution increased and the amount of Cl^- adsorbed by variable charge soils decreased significantly with increasing concentration of SO₄^2- co-existed. However, there was some difference in Cl^- adsorption by constant charge soils in the presence of SO₄^2- when compared with Cl^- adsorption by variable charge soils in the same condit ion. It suggested that the negative surface charge of variable charge soils increased with increasing concentration of SO₄^2- co-existed, but the SO₄^2- co-existed did not influence the negative surface charges of constant charge soils remarkably. The results obtained in this work imply that for variable charge soils, co-adsorption (simultaneously adsorption) and ion-pair adsorption of Cl^- with cations might be involved except electrostatic adsorpt ion when accompanied by univalent cat ions and bivalent or trivalent cat ions respectively. For constant charge soils, only co-adsorpt ion of Cl^- with cations might occur except electrostatic adsorption.

Abstract:Methane emission in the late rice paddy field is characterized by a declining trend with growth of the rice and a positive relat ionship between daily emission rate and air temperature. Application of rice straw in soil (ARSS) could increase methane emission by 51.11%, and application of rice straw on soil surface (ARSSS) only by 33.98%. The rice tillering stage is a peak period for methane emission. At this stage, the methane emitted amounted to 65.6% of the total emitted throughout the whole growth stage of rice. Applying rice straw could increase the proportion of methane emitted at the rice tillering stage. Compared with ARSS, ARSSS decreased methane emission more significantly in the rice tillering stage and at daily peak emission time of 12.00~16.00.The diurnal change in soil temperature at 5 cm depth was highly related with content of methane dissolved in the soil water. ARSSS could remarkably reduce the content compared with ARSS in the layer of cultivated soil of paddy field.

Abstract:Surface charge characteristics of inorganic colloids in soils distributed in different latitudes of China were studied by back-titration method. Results showed that: (1) From south to north, variable surface charge increases with the latitude, which is mainly related to content and composition of soil clay minerals and Fe and Al oxides in the soils. Generally speaking, the higher the content of silicate salt clay in the soil, the higher the permanent negat ive charge and variable negative charge. The higher the contents of Fe and Al oxides, the lower variable negative charge. (2) There exits a peak around pH5 on every Qv-pH curve of inorganic soil colloids from 7 different zonal soils. Maybe it is a result of H⁺ absorption by Si-OH and H⁺ dissociation from Al-OH on the lateral of layer silicates at different pH values. It is possibly related with ZPC of Fe and Al oxides.

Abstract:A hydrodynamic dispersion experiment was done on unsaturated silt loam. Depending on the mass conservation law, formulas to calculate the coefficient of hydrodynamic dispersion were developed. Based on the data of soil water and salt regime measured from the upright soil column, the hydrodynamic dispersion coefficient was calculated, and the relation ship between the hydrodynamic dispersion coefficient and the average pore water velocity was built up. This approach has a clear concept of physics, and the formulas are simple and practical. It can be done with common ap paratus.

Abstract:Research to address spatio-temporal variability of soil chemical properties was conducted with geostatistical method in low hill region in subtropical China. Soil samples from 0- to 15-cm depth were collected at 105 locat ions on a 100- by 100-m grid within a 1.35 km² field in 1985 and again in 1997. Soil properties varied sharply, with available P showing the highest CV and soil pH the lowest. Geostatistical analysis revealed that all the soil chemical properties and their changes between the two sampling time were spatial-structured. The nugget-to-sill ratio showed a strong spat ial dependence for soil pH, and a moderate one for other properties. The ranges for soil properties sampled in 1985 were roughly equal or larger than the diameter of the hills. Changing the land use patterns decreased the ranges for soil chemical properties. The ranges for soil pH and available K were about the radius of hills. The contour map by kriging showed, to a certain extent, a spatial similarity among the estimated values for soil properties in and between the two sampling time. This showed the kridging can be used to analyze the spatio-temporal variability of soil properties.

Abstract:An experiment was conducted in a wheat field of Heilu soil in the south of the Loess Plateau, Changwu County, Shaanxi Province. Efficiencies of urea use and water use were studied in a plot field experiment. Meanwhile the fate of applied nitrogen was investigat ed with ¹⁵N isotope technique. Results showed that crop response to N applied at the rate of 100kg hm^-2 was higher with productiv ity index of 12.1kg grain kg^-1 N, than at the rate of 150kg hm^-2 with productivity index of 6.4kg grain kg^-1 N. Nitrogen application increased water use efficiency from 7.6kg hm^-2 mm^-1 to 9.7~10.5kg hm^-2 mm^-1. ¹⁵N study showed that plant recoveries were in the range of 36.6%~38.4%; N remaining in 0~40 cm soil ranged in 29.2%~33.6% and decreased rapidly with increasing soil depth. About 33%~40% of the N taken up by wheat was derived from the urea applied and the rest, around 2/3 derived from the soil.

Abstract:Investigations were made of dynamic change in phytohormones, including abscisic acid (ABA), indole-3-acetic acid (IAA), gibberellins (GAs) and cytokinis (CTKs) and their effects on the physio- biochemistry in and morphology of rice of three different cultivars, i. e., "Shanyou63" (Sy63), Wuyujing (Wyj) and upland rice "85-15" (85-15) grown in upland soil. The content of ABA increased as compared with that in the CK (waterlogged) and the dynamic change in ABA in rice of different cultivars followed some rules. And the dynamic change in GAs was similar to that in ABA. IAA decreased in roots and increased in leaves at the beginning of the stress period. The change in CTKs content was similar to that in IAA. The results suggested that on the upland soil the act ion of stoma of rice was controlled by IAA as well as ABA and the development of lateral roots was related to the increase in endogenous IAA and the decrease in endogenous CTKs in root.

Abstract:This paper, by using digital image method, studied the structural development of cultivated soils under non-tillage system with simulated laboratory conditions and natural filed conditions. The obtained images qualitatively showed that aggregates in soils became larger, and soil blocks became more compacted under the states of non-tillage. The analytical results of aggregate and pore size distributions clearly showed that smaller aggregates and pores decreased while larger aggregates and pores increased. The results of field soil samples also showed that natural interval rainfall may have a function on adjustment of soil structure, yet it is still uncertain whether non-tillage system is beneficial to soil properties and agricultural production if judged from the soil images and the changes of aggregate and pore size distributions.

Abstract:Fractal dimensions of particle surface were 2.805~2.942 in the plowed layers of 16 crop fields in Sichuan. Among them, sand soil was 2.821, loam soil 2.807, clay loam soil 2.916, and clay soil 2.939. Statistic analysis indicated that fractal dimensions were in highly significant negative correlation with the contents of coarse sand and fine sand, and in very significant positive correlation with the contents of silt and clay. In addition, in the partial correlation with the contents of silt, clay, organic matter and bulk density of soil was highly significant or significant.

Abstract:Comprehensive analysis of out door investigation findings and indoor test data of physical and chemical properties showed that the main properties of the soils on the northern slope of the Qinling Mountain change regularly with the increasing altitude: argillification is getting weaker and weaker, and clay reducing significantly. There are obvious argillic horizons in the middle-low zone on the slope, and no type B horizon in the middle-high zone soil pH value and base saturation decrease from the Wei river valley to the top of the Taibai mountain. It features strong leaching, low Fed, high iron activational degree, low enrichment of aluminium and iron. Soil weathering and development remains in the stage of siallitization. According to the Chinese Soil Taxonomy (Revised Proposal), the soil composition spectrum of the Vertical zones consists of Eum-Orthic Anthrosols (< 750meter)-Hap-Ustic Luvisols (750meter~1400meter)-Hap-Udic Luvisols(1400meter~2500meter) Acid Udic Cambisols(2500meter~3300meter)-Mol-Cryic cambisols (3300meter~3500meter)-Umb-Cryic Cambisols (> 3500meter).

Abstract:The objectives of this study are to understand the law of spatial and temporal changes in soil nutrient quality in the Taihu Lake valley during in period of past two decades, and reveal relationship the change in soil nutrient and its driving forces at a regional level over a long time. A long term sampling experiment was conducted to analyze changes in soil organic matter, total N, available N, available P, and available K in Ganlu Township, Wuxi City. Results show as follows: (i) Soil or ganic matter decreased in the first decade, then increased during the next decade, which is assumed to be related with tillage methods; (ii) Soil total N and available N steadily increased by about 114.4% and 104.7%, respect ively, after 20 years, which is supposed to be associated with the in creasing of the rate of nitrogen fertilizers. At percent, the application rate of nitrogen fertilizers is about 646kg hm^-2 a^-1, which is far beyond the absorption capacity of the crop for growth; and (iii) Soil available P and available K decreased by about 52.3% and 24.2%, respectively, during the period. The content of available P and available K in the soil was only 5.1 mg kg^-1 and 44.8mg kg^-1, respect ively, which is lower than the demand of the crop for normal growth. These changes are believed to a result of inadequate fertilizer input. Only 87. 0kg hm^-12 and 80.4kg hm^-2 were used in 1999. In a word, soil nutrient quality index (SNQI) decreased from 1981 to 1986, then increased after 1986. The analysis of the relationship between the changes of SNQI and the socio-economic factors revealed: (i) The impacts of state policies and tillage methods, cultivating systems on SNQI are very obvious; (ii) Agricultural net input is positively correlated with SNQI (r= 0.832, p< 0.05); and (iii) agricultural net income per hectare is negatively correlated with SNQI(r= 0.915; p< 0.05). Therefore, we can repay the variation of soil nutrient quality of the past and forecast changes in SNQI in future by long-term socio-economic statistics.

Abstract:On the basis of the data of the firsthand observations in the Hemingguan Watershed, a study was made on benefits of comprehensive control in reduction of water and sediment. Results show that rainfall, runoff and sediment are concentrated in the high-water season (May to October), the sequence of annual rainfall and runofff has little declining tendency while the sequence of annual sediment transportat ion declines evidently, which indicat es the turning-better tendency of water and sediment in the watershed after comprehensive control. Among the conservation measures taken, water conservancy practices and conservation engineering play a leading role in reducing water and sediment. The benefit of afforestation and grass-planting is remarkable but noticeable in hysteresis.

Abstract:The filter paper method discussed in this paper shows good sensitivity and reproducibility to unsaturated soil solut ion concentrat ion changes, so it can be used to obtain ion adsorption isotherms in unsaturated soils. It is also quite concordance with the centrifugal method and the ethyl alcohol extract ing method. NH₄⁺ 、K⁺ adsorption isotherms in unsaturated soil obtained with the filter paper method possess ordinary characteristics of ion adsorpt ion isotherms, and can be significantly fitted by Freundlich equation. With a certain equilibrium concentration, the adsorbed amount in solid phase and fitted parameters (k, n) of Freundlich equation increase with increasing solution/soil ratio, indicating that increasing solution/soil ratio can promote ion adsorption reaction in unsaturated soil.

Abstract:Analysis of three different methods of estimating CO₂ emission was carried out by comparing the data obtained from filed determination of soil CO₂ emission from Mat Cryo-sod soil in 1998~1999. Based on the results of the analysis a suitable method of estimating CO₂ emission form Mat Cryo-sod soil was developed. The equation for estimation of diel CO₂ emission is a monadic biquadratic multinomial with instantaneous CO₂ emission flux as dependent variable and time as drive variable. And by deriving the integral to time, the values of the diel CO₂ emission can be obtained. For estimation of annual emission, a multi-nonlinear experiential formula was established with diel CO₂ emission as dependent variable and environment factors as drive variable (such as precipitation, evaporat ion, sunshine, air temperature, soil temperature, etc.). Diel CO₂ emission was calculated using related data from the meteorological station every day, and then the annual accumulated CO₂ emission was obtained.

Abstract:Kinds and contents of organic acids in the compost of chicken feces and their changes were studied. The results indicated that a lot of organic acids came into being and accumulated; the content of organic acids was 88.3 cmol kg^-1 DM reaching the peak after 5 weeks of composting; the content of non-volatile organic acids had two peaks at the third and fifth week of composting separately; the peaks of the volatile acids occurred at the sixth week and ninth week separately. After 9 weeks of composting, the content and number of the kinds of organic acids declined sharply, apart from aromatic acids such as benzoic acid, benzenedicarboxylic acid etc., and their ramification. There were many small molecular organic acids such as butane diacid and their derivatives and some big molecular fatty acids coming into being.

Abstract:Root architecture is closely related to P acquisition efficiency. In the present study, effects of P availability on the root architectural responses of different common bean genotypes were examined. Four common bean (Phaseolus vulgaris L.) genotypes representing different origins and ecotypic races were compared in a strat ified mesh soil potculture system and root architectural parameters were analyzed with computer image analysis. The results showed that root biomass, total root length and total root surface area were decreased under low P conditions. The P efficient genotypes had a larger, finer and shallower root system than the P inefficient genotypes. The basal roots of G19833, G19839 became shallower while those of DOR364 became deeper under low P conditions. The results from this study suggest that there is great genetic variation in root architectural responses to P availability. The genetic potential of root architectural response provides possibility of selecting this trait for improving P acquisition efficiency in common bean.

Abstract:大棚种植具有很好的经济效益和社会效益^[1].近年来它以非常迅猛的速度在我国北方地区发展,据统计,1985年以大棚为主的保护地仅占全部蔬菜耕地面积的1.4%,而到1995年则增至14%^[2].现在这种增长的势头仍未有减缓的趋势,而且大棚种植植物也逐步从蔬菜扩展到果树和花卉.在许多地方,大棚种植成为当地的支柱产业或龙头产业,成为我国土地匮乏情况下有效提高单位面积产值的不可替代的模式.但大棚种植是一种受人为因素作用十分强烈的土地利用方式,这不仅体现在它对环境条件的改变上而且体现在肥水管理上及病虫害防治上^[3～5].