In previous papers, the author determined the flocculation conditions of the puddled water of Kotoh area by Ca application on the basis of the hetero coagulation theory. The results were examined by a laboratory test using 8 flocculation aids. The agreement of the theoretical and experimental results was good and the puddled water was found to flocculate at conditions of Ca concentration >1 — 2 mmol/dm3 or below pH< 5. To realize the condition,gypsum application of lg/dm3 was considered to be the most effective among the aids tested. However,those results were confirmed only in ldm3 volume of the suspensions and it is still unknown that the treatment is effective on the actual conditions of a puddled paddy field. In this paper, gypsum application was examined in the test plots made on the two paddy fields of the area. The effect of basal fertilizer of usual rate on the flocculation was also tested. In addition,the effect of this treatment on the whole effluent load out of the paddy field was estimated. The findings were as follows ;(1)gypsum application rate of 30kg/10a was sufficient to decrease the suspended solid(SS) concentration under 0.1% in 12 hours. The criterion Ca concentration in the puddled water at rapid flocculation was 1—2 mmol/dm3 in the field test, which coincides well with the results of the laboratory test. (2)Basal fertilizer promoted flocculation to some extent and did not hinder the flocculation by gypsum. (3) The rate of 30kg/l0a gypsum was estimated to reduce 70—80% of the whole effluent of SS of the puddled water.
It is recently found that Kanumatsuchi is problem soil due to increment of earthwork with the advance of agricultural use. We investigated the properties of Kanuma pumice stratum and the physical organization of Kanumatsuchi from a view point of agricultural use. Kanumatsuchi consists of pyroclastics originated from Akagi volcano(Gunma prefecture), and its main component is weathered pumice grain of which the diameter is about 2 ~20mm. Taking Kanumatsuchi to pieces,they are classified into four components :(l)Weathered pumice,(2)Small grained pumice,(3)Imogolite,(4)Volcanic gravel.After natural moisture ratio o›j,dry weight ratio a. and specific gravity Gs of each component are determined,moisture ratio (a›i'),void ratio(e / )and porosity (n1’) for the whole Kanumatsuchi are caluculated by the following equations.
n1’= ei'/ (1+en) n”= nn—∑ni’
Where the mark(' )andC ) represents respectively inside value and outside one of pumice grains (Weathered pumice and small grained pumice)for the whole Kanumatsuchi. Degree of saturation of pumice grain Si and one among pumice grains S。are caluculated by the following equations.
S i= ωi Gi=ei S0＝ω”Gs/ei”
As the result,the following facts become clear.
(1) Value of solid phase,liquid phase and gaseous phase are respectively 11.8〜13.5%,61.4〜74.5%, 12.5 〜26.5%.
(2) On natural condition, quantity of mositure(〇)//n)and quantity of void(ω1'/ωn)in weathered pumice is respectively 85.3〜95.9% and 71.9〜90.1% to the whole quantity.
(3) Degree of saturation in weathered pumice grain(S Jis respectively high value(80.6~97.9%).
(4) Degree of saturation among pumice grains is 16.6〜60.5% and quantity of moisture among pumice grains to the whole quantity is relatively low value(2.2〜9.7%)
The effects of different levels(ECiw=0.60, 8,16 dSm-1)of water salinity, gypsum(G= 0.160kg ha-1) and Zinc(Zn=0, 5kg ha-1)on the concentration and uptake of nutrients by rice roots and quality of rice grains were studied in greenhouse. Highly significant(P^0.01)effect of salinity on the concentration and uptake of nutrients by roots and quality of rice grains was found, the adverse effect being more pronounced on BR 6 rice while the exotic CSR 4 appeared more salt tolerant. The concentration and uptake of Ca, Mg and Zn in roots decreased with an increase in salinity. The concentration of Na, Cl and S increased with an increase in water salinity but the uptake of S and Cl was slightly decreased at 8 dSm-1 while 50 per cent yield reduction was at 16 dSm-1. Maximum amount of uptake of Na was at 8 dSm-1 followed by that at 16 and 0.60 dSm-1 for both the cultivars. Application of gypsum and Zn at the rates of 160 and 5kg ha-1 increased the concentration and uptake of Ca, Mg and S, and were effective to decrease the concentration of Na and Cl in rice roots. Salinity significantly reduced the grains and root yields of the rices but GiM and Zn5 had favorable effects on these parameters. Protein contents of the rices varied significantly with the treatments and ranged from 68.8 to 87.5 g kg-1 for CSR 4 and 67.5 to 82.5 g kg-1 for BR 6. Application of G160 and Zn5 separately or in combination improved the protein contents of rice grains, regardless of salinity.
The effect of chisel tillage on the growth and yield of spring wheat seeded in early winter was studied.
1) Spring wheat seeded in early winter germinated under snow and their roots extended more than 30cm during snow season. These growth of roots in snow season promoted sufficient growth of spring wheat in early stage after thawing. The yield of spring wheat seeded in early winter was more than that of wheat seeded in spring.
2) Chisel tillage which broke the soil roughly was possible to adopt the early winter seeding method of spring wheat because the germination of spring wheat occured under snow without moisture stress.
3) The yield of spring wheat of chisel tillage was equal to or more than that of rotary tillage because of the large number of grain per ear and 1000 grain weight.
4) Chisel tillage made ununiform soil physical conditions consisted from tilled and untilled part. The roots distribution of spring wheat concentrated to the tilled part. It seemed that the precipitation and fertilizer also concentrated to tilled part and spring wheat absorbed it efficiently.
Change of landuse from forest to grassland somehow affects soil properties and runoff characteristics of a watershed. Hence, in order to evaluate the effects of the change, two sets of study watersheds, major landuse of which was forest and grassland respectively, were set up for comparison in the Kitakami mountainous area； namely the Nawasirozawa and the Yamaya watersheds, and the Sotoyama—daiiti and the Sotoyama—daini watersheds. Following results were obtained from the research.
(1) The surface layer of grassland soil was shown to have different porosity from that of forest soil in respect to macropores.
(2) Based on the measurements at the watersheds, infiltration capacity was evaluated as medium on grassland soil, while it was large on forest soil.
(3) Regression analysis of direct runoff, lost rainfall and peak discharge vs. rainfall showed that there were statistically significant differences in the regressions between the Sotoyama— daiiti watershed and the Sotoyama—daini watershed. It was proved that these were caused by difference in proportion of grassland and forest in the watersheds.
(4) Based on the measurements, it was analyzed that baseflow possibly decreased by the conversion in the Nawasirozawa and the Yamaya watersheds, while it remained unchanged in the Sotoyama—daiiti and the Sotoyama—daini watersheds.
(5) Distribution factors of the unit hydrograph for each watershed were presented. Runoff hydrographs were also presented based on the typical storms on the watersheds.
(6) Runoff characteristics and their probable changes by the conversion were summarized based on the original soil properties, and the historical, the present and the future landuse.
The main aim of land evaluation is to assess the capability of land resources in relation to particular land uses referring to use on a sustained basis. The potential productivity of soil-plant systems which are possible to introduce in a land area under consideration is important as a general measure of land evaluation. A model combining agro-climatic approaches, analysis on soil water dynamics, and crop water use was introduced successfully to predict the potential and rainfed production of grassland ecosystems in north eastern Hokkaido. The model output, i.e. rainfed production of harvesting grassland in this area, agreed well when the water requirement of grasses was assumed at 400g g-1. This approach was effective to compare benefits of several alternatives in management practices and to give long-term predictions based on the limted information provided by short-term experiments. Data requirements to use this model include climatic items, suth as temperature, reinfall, relative humidity, and sunshine hours, hydrophysical properties of soils, such as water content vs. suction and unsaturated hydralic conductivity vs. suction curves, and water use characteristics of grasses. These physical characteristics of soils and soil-plant systems are indispensable to predict the nutrient limited production of plants, to analyze the dynamics of energy and materials through agro-ecological systems, and assess their impacts to hydrosphere and atmosphere in the context of environmental issues. The importance of soil physical properties and physical approaches in the quantitative land evaluation will grow bigger and bigger in the future.
The lower and the upper limits of soil water content for plant growth were reviewed in terms of water and gas transmission in the soil. Plants can survive for about one month after a lot of rainfall by extracting water held in the soil, but plants exhaust soil oxygen within a few days if soil oxygen was not replenished by gas exchange between the soil and the ambient air. This is a distinct difference between soil water and soil air for plant growth. In case of water, both water potential and hydraulic conductivity are expressed as a function of soil water content, which enables to translate from the water potential to the hydraulic conductivity and vice versa. The lowest limit of soil water called wilting point corresponds to —1.5 MPa for soil water potential or to a value of the order of 10-11 cm/s for hydraulic conductivity, and this limitation was explained well by a single root model. The highest soil water content, which impedes respiration has been studied by use of air porosity, oxygen concentration, oxygen diffusion rate (ODR) or relative gas diffusion coefficient. Even though these studies have proposed critical values of root respiration such as 0.1 to 0.2 for air porosity, 0.1 for a critical oxygen concentration,10 for a critical ODR and 0.005 for relative gas diffusion coefficient, we still have little knowledge of the relation among these physical factors. factor to be uppermost layer in the field supplies the largest amount of water to roots by this time. It for research to confirm either water potential or hydraulic conductivity governs the break potential transpiration. Under field conditions, water transmission ability of the soil should by the amount of water above the break point in the surface soil. Aa gas exchange is inevitable for soil aeration and air porosity is the easiest physical Transpiration begins to decrease at soil water potential between —0.1 and —1.0 MPa and the is important point of the be evaluated measured in the field, relative gas diffusion coefficient as a function of air porosity must be studied further. It is important for gas diffusion to evaluate the amount of isolated air filled pores at saturation and the reflection point or the bubbling pressure in the soil water characteristic curves.
Even though nutrient supply ability of soil has been estimated using extraction method, roots can not absorb nutrients before they reach root surfaces. Soil physics, plant demand and other environmental conditions must be taken into account to evaluate nutrient supply ability of soil. Micro model that was used by Nye and extended by Barber et al., made considerable contribution in the area. But still now, there are some problems that hinders effective utilization of those models. Elongation and development reaction of roots in relation with physical or nutritional conditions of soil, activity of root hair and mycorrhizae, effect of root—induced changes of rooting zone. These are the examples of the hindrances. A macro model that was developed by the author deals behaviours of nitrogen in a paddy soil including mineralization, organization,leaching, denitrification, fertilization, temperature of the soil, absorption by rice plant, development and production of the plant, etc. The model gave some good estimations of experimental outcomes. Many interesting results were obtained by simulation. Utilization of this or other macro models along with micro models will be practical in the area of evaluation of nutrient supply ability and ways of soil management.
Field operarion is related closely with field drainage and soil physical conditions. Criteria for the field operation have been described on basis of soil physical characteristics of fields. However, field condition is extremely heterogeneous and data obtained from the field shows great variebility. In this paper, problems were poited out for processing the soil physical data obtained from fields in order to estimate field condtions. And also, especially with relation to the field drainage, it was examined on basis of a simulation, dimension of samples required to get a representative value of hydraulic conductivity of a field with shrinkage cracks. As a result, it is made clear that a sample which has a diameter two or three times larger than intervals of the cracks would offer the representative value of the hydraulic conductivity of the field.