Soil and Water Resources and Land Sustainable Productivity in the Catchment Area with Intensive Management in Hilly Red Soil Regions,China

Taking an example of Majiayu Catchment Area (14.15 ha) in Taoyuan County of HunanProvince, the soil and water resources dynamics, fertility evolution characteristics andland productivity changing situation were studied. Fixed observation results from 1993to 2002 showed that pools covering about 15% of total area could store up 10% of surfacerunoff, keep 78.1% of eroded soil and 65.4% of lost nutrients. The yearly ratio ofinterception and evapotranspiration in land, storage in pools and drainage was 7:2:1,which ensured the resources and nutrients equilibrium and a benign recycle in thecatchment area system, and benefited the aquatic culture and helped to resist seasonaldrought. Moreover, the results showed that soil erosion modulus decreased significantly,equal to or lower than soil loss tolerance (≤500 tkm-2) in reddish yellow soil regions.Soil organic matter, total and available N content in sloping land, dryland and paddyfield increased steadily (>10%); water storage enhanced by more than 20% in sloping landand dryland in drought season; crop production increased by more than 20%; and productionof trees, fruits, tea and fish as well as land productivity increased yearly.

Water Budget Analysis of Red Soils in Central Jiangxi Province, China

The daily soil water budgets in the red soil areas of central Jiangxi Province,southern China,were investigated with a large-scale weighing lysimeter and runoff plots. From 1998 to 2000,peanuts (Arachis hypogaea L.) and rape (Brassica napus L.) were planted in the lysimeter and in 1999,peanuts were planted in the runoff plots. The soil water budget components including rainfall,runoff,percolation and evapotranspiration were measured directly or calculated by Richards' equation and water balance equation. The results showed that most rainfall,including rainstorms,occurred from March to July,and induced the greatest soil water percolation during the year. The evapotranspiration was still large from July to September when rainfall was minimal. Thus,the lack of synchronization in soil water inputs and losses was disadvantageous to crops growing in this region. Among the soil water losses,percolation was the largest,followed by evapotranspiration,and then soil runoff. Runoff was very small on farmland with crops. It was significantly different from the uncultivated uplands where large-scale runoff was usually reported. The soil water storage fluctuated sinusoidally,with a large amplitude in the rainy season and a small amplitude in the dry season.

Water and heat transport in hilly red soil of southern China:I. Experiment and analysis

Studies on coupled transfer of soil moisture and heat have been widely carried out for decades. However, little work has been done on red soils, widespread in southern China. The simultaneous transfer of soil moisture and heat depends on soil physical properties and the climate conditions. Red soil is heavy clay and high content of free iron and aluminum oxide. The climate conditions are characterized by the clear four seasons and the serious seasonal drought. The great annual and diurnal air temperature differences result in significant fluctuation in soil temperature in top layer. The closed and evaporating columns experiments with red soil were conducted to simulate the coupled transfer of soil water and heat under the overlaying and opening fields’ conditions, and to analyze the effects of soil temperature gradient on the water transfer and the effects of initial soil water contents on the transfer of soil water and heat. The closed and evaporating columns were designed similarly with about 18 °C temperatures differences between the top and bottom boundary, except of the upper end closed or exposed to the air, respectively. Results showed that in the closed column, water moved towards the cold end driven by temperature gradient, while the transported water decreased with the increasing initial soil water content until the initial soil water content reached to field capacity equivalent, when almost no changes for the soil moisture profile. In the evaporating column, the net transport of soil water was simultaneously driven by evaporation and temperature gradients, and the drier soil was more influenced by temperature gradient than by evapo- ration. In drier soil, it took a longer time for the temperature to reach equilibrium, because of more net amount of transported water.

Coupled Transfer of Water and Heat in Red Soil: Experiment and Numerical Modelling

Coupled transfer of soil water and heat in closed columns of homogeneous red soil was studied under laboratory conditions. A coupled model was constructed using soil physical theory, empirical equations and experimental data to predict the coupled transfer. The results show that transport of soil water was affected by temperature gradient, and the largest net water transport was found in the soil column with initial water content of 0.148 m3 m-3. At the same time, temperature changes with the transport of soil water was in a nonlinear shape as heat parameters were function of water content, and the changes of temperature were positively correlated with the net amount of water transported. Numerical modelling results show that the predicted values of temperature distribution were close to the observed values, while the predicted values of water content exhibited limited deviation at both ends of the soil column due to the slight temperature changes at both ends. It was indicated that the model proposed here was applicable.

Water and heat transport in hilly red soil of southern China:II. Modeling and simulation

Simulation models of heat and water transport have not been rigorously tested for the red soils of southern China. Based on the theory of nonisothermal water-heat coupled transfer, a simulation model, programmed in Visual Basic 6.0, was developed to predict the coupled transfer of water and heat in hilly red soil. A series of soil column experiments for soil water and heat transfer, including soil columns with closed and evaporating top ends, were used to test the simulation model. Results showed that in the closed columns, the temporal and spatial distribution of moisture and heat could be very well predicted by the model, while in the evaporating columns, the simulated soil water contents were somewhat different from the observed ones. In the heat flow equation by Taylor and Lary (1964), the effect of soil water evaporation on the heat flow is not involved, which may be the main reason for the differences between simulated and observed results. The predicted temperatures were not in agreement with the observed one with thermal conductivities calculated by de Vries and Wierenga equations, so that it is suggested that Kh, soil heat conductivity, be multiplied by 8.0 for the first 6.5 h and by 1.2 later on. Sensitivity analysis of soil water and heat coefficients showed that the saturated hydraulic conductivity, KS, and the water diffusivity, D(θ), had great effects on soil water transport; the variation of soil porosity led to the difference of soil thermal properties, and accordingly changed temperature redistribution, which would affect water redistribution.

Study on soil water characteristics of tobacco fields based on canonical correlation analysis

In order to identify the principal factors influencing soil water characteristics （SWC） and evaluate SWC effectively, the multivariate-statistical canonical correlation analysis （CCA） method was used to study and analyze the correlation between SWC and soil physical and chemical properties. Twenty-two soil samples were taken from 11 main tobacco-growing areas in Guizhou Province in China and the soil water characteristic curves （SWCC） and basic physical and chemical properties of the soil samples were determined. The results show that： （1） The soil bulk density, soil total porosity and soil capillary porosity have significant effects on SWC of tobacco fiels. Bulk density and total porosity are positively correlated with soil water retention characteristics （SWRC）, and soil capillary porosity is positively correlated with soil water supply characteristics （SWSC）. （2） Soil samples from different soil layers at the same soil sampling point show similarity or consistency in SWC. Inadequate soil water supply capability and imbalance between SWRC and SWSC are problems of tobacco soil. （3） The SWC of loamy clay are generally superior to those of silty clay loam.

Determination of Water Colltent in Clayey Red Soil Using Techniques Based on Measurement of Dielectric Constant

Two time-domain reflectometry (TDR) systems and a new impedance measuring instrument, Thetaprobe,which are based on determination of soil dielectric constant, were used to measure water content of clayeyred soil to eraluate the accuracy of these instruments. The results indicated that these instruments shouldbe carefUlly re-calibrated before being applied in clayey red soil. With a new calibration curve fed into one ofthe TDR systems tested, nase system, the measured data compared well with tho8e by standard oven-dryingmethod.

Soil Erosion Changes over the Past Five Decades in the Red Soil Region of Southern China

This paper reports the dynamic changes of soil and water loss in the red soil region of Southern China since the 1950s. The red soil region covers eight provinces: Jiangxi, Zhejiang, Fujian, Anhui, Hubei, Hunan, Guangdong and Hainan. From the 1950s to 1986, the annual rate of soil erosion increased by 3.4%. From 1986 to 1996 and from 1996 to 2000, the annual rates of soil erosion decreased by 2.0% and 0.32%, respectively. Field surveys showed that from 2000 to 2005, the area of soil and water loss decreased annually by 1.2%. This decrease was a result of large-scale erosion control activities across China. Although the eroded soil has been restored, the restoration process is very slow and full restoration will take a long time. Our report suggests that controlling soil and water loss is a challenging task, and additional measures must be taken to effectively control the soil erosion in the red soil region.

Different Fertilization Modes of Sugarcane in Latosolic Red Soil of Guangxi

[Objectives] This study aimed to compare the effects of water-fertilizer integrated drip irrigation modes and traditional fertilization mode on growth,yield,production costs and economic benefit of sugarcane in latosolic red soil of Guangxi. [Methods]A field test was conducted. [Results] The agronomic traits and comprehensive economic benefit of sugarcane under the water-fertilizer integrated drip irrigation modes were superior to those under the traditional fertilization mode. Among them,the comprehensive economic benefit of sugarcane with special granular fertilizer as the base fertilizer and water-fertilizer integrated drip irrigation as topdressing were the highest,increased by 15 813 kg/ha,an increase of 15. 8%. Considering the cost input,the comprehensive economic benefit increased by 5 676 yuan/ha. [Conclusions]Taking the production cost,economic benefit and input-output ratio into account,it is recommended to promote the application of water-fertilizer integrated drip irrigation mode in bases with water and fertilizer equipment conditions.

In-Situ Evaluation of Evaporation in Layered Soils （Tukulu, Sepane and Swartland）

Knowledge about the influence of soil layers on evaporation is essential for the optimization of infield rainwater harvesting （IRWH） in the semi-arid areas of the Free State province of South Africa. Among the soils earmarked for 1RWH development include the Tukulu, Sepane and Swartland soil types that have contrasting soil layers. These soils have to capture and store rainwater within the soil profile layers away from the evaporation zone. To determine how the three soils release and deliver soil water at the evaporating site, a 21-day evaporation experiment was conducted on pre-drained monoliths. Instantaneous soil water content （SWC） from in-situ and soil water characteristic curve （SWCC） from laboratory was measured. Separate soil samples of 15 mm thickness were also evaporated under the same conditions to establish the extent of drying and hydraulic gradient at the soil surface. The Darcian evaporative flux and unsaturated hydraulic conductivity （K-coefficient） were also determined. At the surface suctions of magnitude greater than 1,500 kPa were observed from all monoliths. Total contributions to evaporation from the Tukulu, Sepane and Swartland were 43, 51 and 70 mm, respectively. The low contributions were explained by the presence of the prismacutanic C-horizon in the Tukulu and Sepane at respective depths of 600 and 700 mm. This layer was associated with the steepest suction gradient that restrained further upward fluxes by subsequent lowering for the K-coefficient with more than two orders of magnitudes within a narrow range of SWC. However, the presence of the pedocutanic B-horizon at depths of 300 mm undermined this restrictive function through the appreciable capillary activity demonstrated by clays at near evaporating surfaces. The shallowness and deficiency in structure of the Swartland was consistent with the high contribution to evaporation that gave this soil a dry soil water regime. It was therefore concluded that the Tukulu offered soil profile layers that could reasonably satisfy the soil water conservation requirements for IRWH.

Effects of gravel on the water absorption characteristics and hydraulic parameters of stony soil

The eastern foothills of the Helan Mountains in China are a typical mountainous region of soil and gravel,where gravel could affect the water movement process in the soil.This study focused on the effects of different gravel contents on the water absorption characteristics and hydraulic parameters of stony soil.The stony soil samples were collected from the eastern foothills of the Helan Mountains in April 2023 and used as the experimental materials to conduct a one-dimensional horizontal soil column absorption experiment.Six experimental groups with gravel contents of 0%,10%,20%,30%,40%,and 50%were established to determine the saturated hydraulic conductivity(K_(s)),saturated water content(θ_(s)),initial water content(θ_(i)),and retention water content(θ_(r)),and explore the changes in the wetting front depth and cumulative absorption volume during the absorption experiment.The Philip model was used to fit the soil absorption process and determine the soil water absorption rate.Then the length of the characteristic wetting front depth,shape coefficient,empirical parameter,inverse intake suction and soil water suction were derived from the van Genuchten model.Finally,the hydraulic parameters mentioned above were used to fit the soil water characteristic curves,unsaturated hydraulic conductivity(K_(θ))and specific water capacity(C(h)).The results showed that the wetting front depth and cumulative absorption volume of each treatment gradually decreased with increasing gravel content.Compared with control check treatment with gravel content of 0%,soil water absorption rates in the treatments with gravel contents of 10%,20%,30%,40%,and 50%decreased by 11.47%,17.97%,25.24%,29.83%,and 42.45%,respectively.As the gravel content increased,inverse intake suction gradually increased,and shape coefficient,K_(s),θ_(s),andθ_(r)gradually decreased.For the same soil water content,soil water suction and K_(θ)gradually decreased with increasing gravel content.At the same soil water suction,C(h)decreased with increasing gravel content,and the water use efficiency worsened.Overall,the water holding capacity,hydraulic conductivity,and water use efficiency of stony soil in the eastern foothills of the Helan Mountains decreased with increasing gravel content.This study could provide data support for improving soil water use efficiency in the eastern foothills of the Helan Mountains and other similar rocky mountainous areas.

Effects of biochar amendments on soil water retention characteristics of red soil at south China

Biochar has been extensively used for the improvement of soil water retention.However,the effects of various biochars were not well determined.The objectives of this study were to investigate the effects of three biochars[biochars made from bamboo(Bambusaceae),rice straw(Oryza sativa),and tobacco stem(Nicotiana L.)]on soil physical properties and the water retention characteristics of red soil at southeast China.The air-dried soil samples were mixed with ratios of 2%,5%,and 10%(w w^(−1))BC(bamboo biochar),RC(rice straw biochar),and TC(tobacco biochar),respectively,and evaluated for changes in soil bulk density(BD),soil saturated water content,field capacity,capillary porosity and soil hygroscopic coefficient.The results showed that BD decreased significantly with the application of the three types of biochar,total soil porosity and capillary porosity increased with the increase of the biochar ratio.The soil hygroscopic coefficient,wilting moisture capacity,saturated water content,and field capacity were significantly affected by the application of the three types of biochar.Compared with the other two treatments,the BC showed the best effects on soil water characteristics.BC treatments with addition ratios of 2%,5%,and 10%significantly decreased BD by 6.55%,18.03%,and 36.07%,respectively.Moreover,saturated water content and field capacity were increased by BC.BC treatments significantly increased the readily available water by 32.65%,42.49%,and 50.01%,respectively.However,the increased non-readily available water induced by the high ratio of biochar addition was not easily utilized by plants.Our results suggested that the biochar amendment can improve soil structure,decrease soil BD,boost soil porosity and capillary porosity,and increase soil moisture constant,and 2-5% of BC was recommended in the field condition.

Characteristics of In-Situ Soil Water Hysteresis Observed through Multiple-Years Monitoring

A soil water retention curve (SWRC) is an essential soil physical property for analyzing transport and retention of water in a soil layer. A SWRC is often described as a single-valued function that relates the soil water potential ψ to volumetric water content θ of the soil. However, an in-situ ψ − θ relation should show soil water hysteresis, though this fact is often neglected in analyses of field soil water regimes while long-term in-situ soil water hysteresis is not well characterized. This study aimed at probing and characterizing in-situ ψ − θ relations. The developments of large hysteresis in the in-situ ψ − θ relations were observed only a few times during the study period of 82 months. Any of the large hysteretic behaviors in the ψ − θ relations began with an unusually strong continual reduction in ψ. The completion of a hysteresis loop required a recorded maximum rainfall. Because the study field had very small chances to meet such strong rainfall events, it took multiple years to restore the fraction of soil water depleted by the unusually strong continual reduction in ψ. While wetting-drying cycles had occurred within a certain domain of ψ, hysteretic behaviors tended to be so small that the in-situ ψ − θ relation can be approximated as a single-valued function of θ(ψ). These observed patterns of the in-situ ψ − θ relations were characterized by kinds of difference in dθ/dψ between a drying process and a wetting process at a given ψ. Thus, more amounts of experimental facts about wetting SWRCs in parallel with drying SWRCs should be needed for correct modelling, analyzing, and predicting soil water regimes in fields. It is also necessary to increase our understandings about the long-term trends of occurrences of extreme weather conditions associated with possible change in climate.

Formation and Water Stability of Aggregates in Red Soils as Affected by Organic Matter

The water stability of aggregates in various size classes separated from 18 samples of red soils under different managements, and the mechanisms responsible for the formation of water-stable soil aggregates were studied. The results showed that the water stability of soil aggregates declined with increasing size, especially for the low organic matter soils. Organic matter plays a key role in the formation of water-stable soil aggregates. The larger the soil aggregate size, the greater the impact of organic matter on the water stability of soil aggregates. Removal of organic matter markedly disintegrated the large water-stable aggregates (> 2.0 mm) and increased the small ones (< 0.25-0.smm) to some extent, whereas removal of free iron(aluminium) oxides considerably destroyed aggregates of all sizes, especially the < 0.25-0.5 mm classes. The contents of organic matter in water-stable aggregates increased with aggregate sizes. It is concluded from this study that small water-stable aggregates (< 0.25-0.5 mm) were chiefly cemented by Fe and Al oxides whilst the large ones (> 2.0 mm) were mainly glued up by organic matter. Both free oxides and organic matter contribute to the formation and water stability of aggregates in red soils.

Characteristics of Soil Porosity and Changes of Soil Water Content in Eucalyptus Plantation

Objective] This study almed to investigate the characteristics of soiI total porosity （STP） and various factors affecting soiI water content （SWC） in eucalyptus pIantation （EP）, thereby providing references for soiI water utiIization in eucalyptus pIanting in the red soiI hiI y region of South China. [Method] In the same cIimatic region, soiI sampIes were coI ected from surface soiI Iayer （A）, iI uvial horizon （B） and parent material horizon （C） in the upper sIope, middIe sIope and Iower sIope of eucalyptus pIantation, native forest and pine forest, respectiveIy, to determine the soiI porosity and soiI water content and analyze changes and various infIuencing factors of soiI water content in horizontal and vertical direction. [Result] Average soiI porosity in eucalyptus pIantation, native forest and pine forest was 45.9%, 41.4%and 55.3%, respectiveIy; soiI water content in these three forest stands was 13.3%, 13.4% and 15.5%, respectiveIy. In addition, soiI water content in these three forest stands exhibited no significant differences （P＆gt;0.05） among different soiI profiIes and sIope positions, but soiI water content in surface soiI Iayer varied significantIy （P＆lt;0.05） among different forest stands; in the horizontal direction, soiI water content exerted an extremeIy significant positive correIation with total coverage. [Conclusion] Total coverage of canopy Iayer, herb and Iitter Iayer is one of the most critical fac-tors affecting the changes of soiI water content in surface soiI Iayer of forest stands.

Effects of Combined Application of Water Retaining Agents and Organic Materials on Water Holding Characteristics of Yellow Brown Soils in Hilly Areas

[Objective] The aim was to reduce fertilizer and water losses caused by surface runoffs in rainy season and provide scientific references for soil moisture in arid season. [Method] The application proportion of complex water-holding organic materials was determined by multi-factor mixture experiment and the curve changes of soil moisture characters were tested to analyze water-holding capacity and water availability of soils. [Result] The initial moisture content of soil with different mixture proportions improved in varying degrees. For example, when water-retention agents reached 0.4% and 0.6% of soil weight, soil moisture contents were 69.0% and70.5%, respectively, which showed significant differences with the control（S0.0）. Soil dehydration terms in different treatments all extended, prolonging in the range of4.6-14 d. [Conclusion] The applications of water-retention agent and organic material would improve water-holding capacity of hills and low mountains, and initial moisture content and dehydration cycle tend to be volatile upon mixture proportion. Therefore,it is necessary to adjust soil fertility, crop species, and irrigation to meet crop demands on fertilizer and water.

Soil water characteristics in mountain poplar stand and its benefits to soil and water conservation in loess hilly region

The soil physical properties,its water characteristics and the benefits to soil and water conservation in mountain poplar stand were determined and studied. The results of the study show that the compaction in soil profile is relatively homogeneous.the specific gravity and volume weight of soil increase with deepening of soil horizon. The water infiltration rate of soil in the stand is 17,6 times as high as in rangeland.Owing to the intense absorption of water by root system of plants,a drying layer is formed in soil horizon from 2.3 m to 2.7m,showing that the subsoil moisture is in the state of deficit. The annual water storage capacity in 2 m of soil horizon is 360 mm 370mm,or 63% 65% of annual precipitation. Compared with farmland,mountain poplar stand reduces the surface runoff and soil loss by 70% and 99%,respectively,indicating the great benefits to soil and water conservation.

Design and Application of Automatic Test System of Soil Water Characteristic Curve

[Objective] In order to better meet the requirement of crops on a more and more accurate water content under various planting environment of modern agri-culture, an automatic test system of soil water characteristic curve was designed by combining the conceptions of soil moisture content and soil water potential. [Method] Electronic soil moisture tension meter was used to determine the real-time tension value of soil moisture in the tested container, and the electronic Weigh sensor was used to determine soil Weigh. Minusing method was used to calculate soil moisture content, based on which the soil water characteristic curve was plotted. [Result] Through the filed survey of 2 different kinds of soil in Jiangsu Province, the results were as fol ows： soil of different composition showed different trend in soil water characteristic curve that the soil water characteristic relation of the sandy soil in the old course of the Yel ow River in Xuzhou was Y=-0.000 2X3＋0.027 7X2-1.644 5X＋38.161, R2=0.991 9; while the soil water characteristic relation of the saline-alkali soil in Jinhai Farm of Dafeng was Y=-0.00 2X2-0.426X＋39.905, R2=0.991 3. [Con-clusion] The automatic test system of soil water characteristic curve soil water char-acteristics curve could reflect soil moisture content and soil water potential, as wel as reflect the effectiveness of soil water to plant growth, providing basis for the sci-entific irrigation.

Rice Yield and Water Use as Affected by Soil Management Practices

A field experiment was conducted at the Shenyang Experimental Station ofEcology, Chinese Academy of Sciences, to study the effects of soil management practices on water useand rice (Oryza sativa L.) yield in an aquic brown soil during 2001 and 2002. A completely randomexperimental design with three replications was employed, having four soil management practices astreatments, namely: an undisturbed plow layer (CK), a thin plastic film (TN), a thick plastic film(TI) and subsoil compacting (CP). Results indicated no significant differences among all treatmentsfor rice biomass and grain yields. Also, water consumption was about the same for treatments TN andCK, however the treatments TI and CP were much lower with more than 45% and 40% of the irrigationwater in the treatments TI and CP, respectively, saved each year compared to CK. Therefore, wateruse efficiency was higher in the treatments TI and CP. These results will provide a scientific basisfor the water-saving rice cultivation.

Prediction of soil–water characteristic curve for Malan loess in Loess Plateau of China

To predict the soil-water characteristic curve(i.e.SWCC)of natural and remoulded Malan loess from soil physical properties,one-point methods for determining the SWCC that are much simpler than experimental methods are proposed.The predicted SWCC is presented in the form of the BRUTSAERT equation,in which the four model parameters can be estimated from soil physical properties using the best correlations obtained in the present study along with one measured data point.The proposed one-point methods are validated using the measured SWCC data reported in the literature.The results of validation studies suggest that the proposed one-point methods can provide reasonable prediction of the SWCC for natural and remoulded Malan loess.The measured data point should be within the transition zone;the measured suction is suggested between25to100kPa for natural loess,while between100to500kPa for remoulded loess.