果樹の生育に及ぼす土壤の物理的組成の研究

Abstract

1. The soil properties, top growth and root disribution of young peach seedlings were compared at Hiratsuka on triplicated plots under six treatments-clean cultivation, straw mulch and cover crop with and without fertilizing respectively-in 1950 and on triplicated plots under three treatments-clean cultivation, straw mulch, and cover crop without fertilizing-in the field with better subsoil in 1951.2. Soil temperature of limiting the root development is about 35°C and optimum temperature is 24°C, and it is about 10% soil moisture that the top lineal growth of peach trees is ceased and optimum soil moisture for peach trees is 20-40% on dry basis. It was found that in the experiments in 1950 straw mulch was effective in maintaining the soil temperature in optimum range. The lowest soil moisture of the soil surface was found in the clean cultivation plots. In the soil between 5 to 10cm deep, however, the cover crop plots had the lowest soil moisture, which was less than 10%, compared with other treatments. From the experiment in 1951, the same effects of soil management upon soil moisture and soil temperature were found in 10cm depth of surface soil. Soil temperature 10cm deep in clean cultivation plots was 35°C on August 10, 1951, but in mulched plots it was lower than 35°C even on soil surface. Soil temperature in cultivation plots was about 24°C in 5cm depth before May 1 and also in 20cm depth on July 3, which was the optimum temperature for tree growth. On the contrary, temperature on soil surface of mulched plots just rised to 24°C on June 1 for the first time. Differences of soil moisture contents among treatments were greater in hotter and drier soil condition, and then soil moisture content in 5-10cm depth was 10-14% in cover crop plots, 16-18% in clean cultivation plots, and in mulched plots it was about 20% unrelated with soil depth.3. It seems to be principally due to the effect of higher soil temperature in early season in 1951 that the peach seedlings showed the better top growth in clean plots than in mulch plots until early July. Subsequent rapid top growth of seedlings was made in mulched plots, growing as large as in clean cultivation plots in late August. This rapid growth was perhaps owing to the more developments of fibre roots of peach seedlings in surface mulched soil 0-10cm deep than in clean cultivation plots. In 1950 experiment, the most root development in 5cm deep was found in mulched plots. In 5-20cm soil layer root development of mulch plus fertilizing was best, and that of clean cultivation plus fertilizing was next. Root of cover crop plus fertiliztng plots and especially cover crop plots developed poor as top growth. The same characteristic root systems as those of the previous experiment were obtained from different soil managements in 1951 experiment. In the lower parts of the soil under 30cm depth, the differences in soil temperature and soil moisture among soil managements were never found, and therefore root development under 30cm of soil in every treatment was nearly identical.4. The potassium content of the leaves and exchangeable potassium in the topsoil were incrased significantly by mulching. There is no increasing of available phosphorus content even in 10cm depth soil of fertilized plots. In experiments in 1951, much the same as those in 1950, cover crops system caused the least nitrogen content of peach leaves. The difference of organic matter contents was seen only on top soil, but straw mulch caused the best, cover crop the next and clean cultivation the least increasing of them.