Sulfuric acid solution diffusions into horizontal allophanic soil column, including less than 2 mm aggregates, were measured to estimate the acid rain influences on this soil and to calculate pH diffusion coefficient. pH profile following sulfuric acid solution diffusion into this soil for 15 days was predicted by the method of mixing cell model which were combined with chemical equilibrium equations established in batch experiments. The results obtained were summarized as follows ;
1. pH profile following diffusion for 15 days was differ from smooth distributions such as water diffusion or thermal diffusion in homogenous medium. pH was changed sharply in the range of 0.3〜0.7 cm from acid solution reservoir.
2. The average soil pH diffusion coefficient obtained with sulfuric acid solution diffusion was 7×10-8cm2/s.
3. Effects on pH profile derived from proportion of soil that was concerned in reaction with acid solution and from degree of sulfuric ion adsorption expressed by Langmuir type adsorptive equation were analyzed. Sensitivity analysis with two parameters for pH profile gave suggestions that proportion of active soil had large influence on pH profile than that of sulfuric ion adsorption.
4. The results of simulations, with reduced proportion of active soil and sulfuric ion adsorption, for pH profile after 15 days had a sharp pH change similar to measured profile. Simulations were succeeded in error less than 土pH 0.1 compared with measured value.
5. Simulation results implied that advancement of pH diffusion was restricted by the formation of new and high pH boundary conditions in the neighborhood of acid solution reservoir.
The purpose of this study is to make influence to consolidation of the paddy fields and soil physical properties by advanced technique, which contributes to promote new technique. We selected implementing advanced rice growing farmers, and investigated their growing method and soil of paddy fields. Location of survey site in this research in the paddy fields conducted shallow Under-drainage in Fukuroi city of Shizuoka prefecture. The following items on paddy fields such as soil profile, soil physical property, water content, bearing capacity, and Under-drainage discharge, water quality were measured. In order to examine the influence of under-drainage, the effect of shallow under-drainage was pursued with these obtained results. As a result, it was cleared that soil dryness progresses and soil structure progresses. Also this investigated paddy field has already been constricted under-drainage, therefore the workability of agricultural machine like rice transplanter and harvest-machine like combine were improved. In addition to the introduction new growing technique of field drainage with conversion of paddy fields into large-sized and multi-purpose one, is also being considered as significant thing. Therefore it can be considered that shallow under-drainage with sheet pipe is efficient to field drainage.
Soil reclamation (both desalinization and desodification) is frequently required in arid and semiarid regions in order to keep the irrigated agriculture sustainable. Intermittent and continuous ponding are the most widely used leaching methods in this aspect. This study examined the efficiency of these two leaching methods in desalinization and desodification of two saline and sodic soils : a gypsyferous sandy loam and a nongypsiferous clay loam. Soil columns (100 and 200 mm high) were leached with irrigation water (EC=1.8 dS/m, SAR = 3.2) under both methods. Effluent from the columns was collected continuously, and its cationic and anionic composition was analyzed. Intermittent ponding was more efficient than continuous ponding in desalinization and desodification of the clay loam. By contrast, in the sandy loam, efficiency was similar under the two leaching methods in desalinization, whereas desodification was more efficient under intermittent ponding. In the clay loam where soil aggregation is higher, unsaturated water flow that occurs in micropores under intermittent ponding resulted in higher leaching efficiency on desalinization compared with continuous ponding under which condition water flow is saturated and much of the water is conducted by the macropores. Conversely in the sandy loam, unsaturated water flow prevails under both intermittent ponding and continuous ponding explains the similar leaching efficiency on desalinization observed under the two leaching methods. Soil desodification was enhanced by intermittent ponding in both soils, because Na replacement is a slow process which is controlled by intra-aggregate diffusion of Na+ and Ca2+ and the rate of gypsum dissolution. In the clay loam, the rate of intra-aggregate diffusion of Na+ and Ca2+ determines the efficiency of desodification, and in the gypsiferous sandy loam, the rate of gypsum dissolution determines the efficiency of desodification.
A new method that can measure dissolved oxygen (DO) in soil solution and redox potential (Eh) and others in several constant depths was developed. This method was used at two paddy fields, with different organic content, under farming conditions over three years. Findings are listed as follows.
① The installation was made up of a simple box (50 cm X 50 cm X 60 cm) and other instruments. Filters for sampling soil solutions and several electrodes of redox potential were set horizontally at the observation box (open lysimeter).
② Concentrations of DO in inundation were 5-8 mg/L during the ponding irrigation period. After translation of rice plants, DO in soil solution of plow layer(at 3-4 depths) became about 2 mg/L during the irrigation period. DO in soil solution increased to 5-8 mg/L during the nonirrigation period.
③ The value of Eh in plow layer decreased gradually after inundation and became a reduction layer (about —150 mV) until mid-summer drainage. If the period of mid-summer drainage did not received rain for seven days, the plow layer became oxidation layer. But the higher Eh values in the plow layer would return to similar low Eh before mid-summer drainage when inundation continued over two weeks. After the ponding water was released the values of Eh gradually increased and became the oxidation layer (over 400 mV). As the above results show, the new method clarifies that DO and Eh values of plow layer at constant depths show seasonal fluctuation.