Studies were done on the effects of long-term use of compost made of cow manure and barks on the physico-chemical properties of andosol and yields of horticultural crops. The aim of the studies was to set standards for soil diagnosis and minimum fertilizer application schedules. The yields of cabbages and Japanese radishes were greatly affected by the weather conditions, and they varied considerably, almost two folds between the lowest and highest yields in cabbage heads and more than three folds in the weight of Japanese radish roots. The effect of the application of the compost was not apparent in the first year on the yields of cabbages and Japanese radishes. But the yields increased more than 10% to more than 30% in the following years. However, their yields were not much greater than those in the plots that had only chemical fertilizers, though the compost was given to them for many years. This trend was seen in the yield of Japanese radish roots. If the soil contained a certain amount of phosphorus, the effect of phosphorus in the compost on the yields was not obvious. With regard to the physical property of soil, the difference between the sold phases of the plots with and without compost applications tended to widen. Even when bases were applied equally, the amount of bases in the soil decreased rapidly in the plots with good absorption property while they accumulated in the plots where crop yields were low with not nitrogen fertilizer. Cation exchange capacity (CEC) increased even in the increased with application of the compost and fused magnesium phosphate. CEC increased even in the no-nitrogen plots when phosphorus was applied. Total carbon and total nitrogen increased every year when 3 t/lOa of compost was applied yearly, though the amounts had some fluctuations.
Anthropogenic effects on peat soils were investigated by comparing the physical properties of soils taken from undisturbed natural moss field, adjacent rice fields, adjacent upland fields and adjacent windbreak areas in Bibai, Hokkaido Japan. Following the soil profile observations, in situ water contents, bulk densities, particle densities, ignition losses, and shrinkage index were examined in the laboratory. In lowmoor peat areas, the upland fields were relatively dry and the shrinkage indexes were relatively high. Both in lowmoor and transitional moor peat areas, the bulk densities of surface soils in rice fields and upland fields were very high due to the efforts of soil dressing continued up to now. In the highmoor peat area, in situ water contents were as high as 1,000 to 1,500% but the ignition losses were not necessary higher than transitional moor. Against our expectation, the shrinkage degrees versus water contents of highmoor were lower than those of lowmoor.
Recently nitrate outflow from the agricultural area became one of big problems in Japan. We continue the long term experiment on nitrate removal in the flooded paddy field from 1991. Experimental plots consist of four plots ; weed plant, rice, non-plant and covered plot. In the non-plant plot any plant does not grow, but some of algae grow. In the covered plot, no algae grows due to the shield of the light. Natural water with high nitrate concentration about 20 mg L_1 are supplied to each plot continuously. Nitrate is removed through the flow process in the plots by denitrification and the uptake by the plant. Average values of nitrate removal rate for 8years are 0.30gm 2d_1 in a weed plot and 0.27gm 2d-1 in a rice and a non-plant plots. Nitrate removal rates gradually decreased in the first few years, but now they keep the ability of nitrate removal after 9 years. In order to clarify the influence of plant growth and algae on nitrate removal these data are examined by the nitrate removal equation as shown in eq. (2), which indicates the relation between the nitrate removal by denitrification (Ro) and nitrate concentration of water (X) and temperature (T).