Discussion of soil degradation mechanism and efficient irrigation schedule in irrigated arid lands

1.在温室内进行了土水调控微灌蔬菜栽培试验。结果表明，适宜的土壤水分范围是叶菜类蔬菜产量和品质的保证。采用再生纸覆盖、黑色聚乙烯薄膜覆盖和银膜覆盖3种不同覆盖方式进行大豆栽培试验。在相同微灌量下，再生纸覆盖试验田大豆生长最好，水分利用效率也较高，可作为节水栽培。通过对日本西部鸟取县砂田灌溉参数的实测，建立了模拟模型，推荐了水箱微灌制度。利用日降雨量、蒸散量和掺沸石砂的水分特征曲线进行模拟。将人造沸石的特性应用于微灌系统， ...更多信息 2.进行了短期降雨强度变化对土壤影响的试验研究。在恒定雨强试验中。地壳形成于初始阶段。与恒定雨强试验不同，增加雨强试验中土壤流失量随着时间的推移逐渐增加。但粘性土和桑迪流失量增加的原因不同。在降低降雨强度的试验中，土壤流失量随时间的延长而减少。降雨强度的变化强烈影响粘性土的飞溅率。在裸坡上进行了人工降雨试验。本试验测定了裸露坡面上形成的细沟网络和土壤径流的时间变化。分析了径流土壤的粒度组成，探讨了土壤硬度、原土粘粒含量与土壤流失的关系。研究了粘土矿物、粘土含量和平衡液盐度对蒙脱石和伊利石钠钙交换选择性评价的影响。采用时域反射法（TDR）测量了钠钙镁矾的介电常数ε和体电导率（EC）。尽管用蒸馏水制备的膨润土样品具有相当大的EC值，其最大峰值为体积含水量θ=0.60 m^3 m^<-3>，饱和度θ的最低限值：钠基膨润土为3.88 dS m^<-1>，钙基膨润土为1.45 dS m^<-1>。由于能量损失，钠基膨润土在θ=0.45 ~ 0.87 m^3 m^-之间，钙基膨润土在θ=0.36 ~ 0.50 m^3 m ^-之间，TDR波形几乎完全衰减<-3>。提出了一种由多步出流和蒸发相组成的两阶段快速估算土壤水分保持函数和导水率函数K的方法。该函数由平衡出流数据和湿度数据的曲线拟合确定。利用蒸发数据和最终含水量剖面反推K函数。通过与其它可靠方法的K值比较，验证了该方法的可靠性。少

1.Vegetable cultivation in a greenhouse was performed using the microirrigation under soil-water control. It was shown clearly that the yield and quality of leafy vegetables were produced by suitable soil water range. The soybeans cultivating experiments were compared using three different types of mulching ; recycled paper mulch, black poly-film mulch, and silver film mulch. Growth of soybeans in the experimental field under recycled paper mulch was the best under the same amount of microirrigation, the water use efficiency was also high, and it was useful as water-saving cultivation. The microirrigation schedules with tank systems were recommended using the simulation models with irrigation parameters measured in the Tottori sand fields located in the west part of Japan. The simulation was carried out using daily rainfall, evapotranspiration and water retention curves of sand mixing with artificial zeolite. By applying characteristics of artificial zeolite to the microirrigation sche … More dules, saving amount of irrigation water were estimated for vegetables cultivated in Tottori sand fields.2.An experimental study was made on the effect on the soil of changing rainfall intensity in a short period of time. In the test on constant rainfall intensity. crust was formed at the initial stage. Unlike the constant rainfall intensity test, the soil loss gradually increased with the passage of time in the test on increasing the rainfall intensity. The cause for soil loss increase, however, differs between clayey soil and sandy soil. In the test on decreasing the rainfall intensity, the soil loss decreased with time. A change in the rainfall intensity strongly affected the clayey soil in terms of splash rate. Experiments were carried out by supplying artificial rainfall on the bare slope. In this experiment, rill networks that develop on the bare slopes and the time variations of soil run-off were measured. Particle size of run-off soil was analyzed and the relationship between the soil hardness, clay content of original soil and soil loss was investigated. And confinned that the change of configuration of soil surface was deeply influenced by the clay content of soil.3.The effects of clay minerals, clay contents and salinities of equilibrated solution to evaluate Na-Ca exchange selectivity using Montmorillonite and Illite were studied. The dielectric constant ε and bulk electrical conductivity (EC) of Na- and Ca-bentonites were measured by time-domain reflectometry (TDR). Bentonite samples though prepared by distilled water provided considerable magnitude of EC having a maximum peak value at volumetric water content θ=0.60 m^3 m^<-3>, the lowest limit of θ for saturaion : 3.88 dS m^<-1> for Na-bentonite and 1.45 dS m^<-1> for Ca-bentonite. Due to energy loss, TDR waveform was almost completely attenuated between θ=0.45 and 0.87 m^3 m^- for Na-bentonite and between θ=0.36 and 0.50 m^3 m^<-3> for Ca-bentonite. A two-stage laboratory method which consists of multi-step outflow and evaporation phase was developed for rapid estimation of the soil water retention function and hydraulic conductivity function K from near-saturation to air-dry. The function was determined by curve-fitting of the equilibrium outflow data and psychrometric data. The K function was estimated inversely using evaporation data and final water content profile. Compared with K data from other reliable method, reliability of the presented method was verified. Less