Joint study on the fruit growing at sleep slope orchards

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Most of citrus orchards of western part of Japan are located on steep slope. Fifty percent or more acreage are located on the slope above 15ﾟ. Soil erosion is one of the most serious problems in those orchards.It has been reported that soil erosion reached an amount of 25.6t/ha/year in an orchard of clean culture. Precipitation of the year was 1224mm. By introducing sod culture, the followings can be expected. (1)Improvement of soil texture ; (2)Prevention of surface soil erosion ; (3)Organic matter supply as a source of humus and (4)Propagation of useful microorganisms.Roost of bahiagrass penetrate into somewhat consolidated layer of the soil and make the soil porous. Decayed leaves of the grass are transformed into humus. On the root surface of bahiagrass, VA mycorrhizal fungi proliferates.It is observed that VA fungi population on the citrus roots (Poncirus trifoliata) is high where bahiagrass is introduced for sod culture. VA fungi may contribute to absorb phosphate by the citrus r … More oots from the soil where phosphate is scarce. Although sod culture had been introduced to commercial citrus orchards, it has not been successful in Japan. Citrus growers have believed the clean culture is the best for high grade fruit production. However, we are now on the stage when soil management must be fundamentally reconsidered.Previously grasses introduced for sod culture was mainly originated in northern Europe. These grasses grow so vigorously from late March to April. Competition of nutrient absorption between citrus roots and the grass is very sever. It is very important to preserve spring cycle shoots for high yield. Because flower differentiation and fruit bearing are stable on those shoots. If the grass might depress the growth of spring cycle shoots, the significance of sod culture will be lost. To overcome the competition in the nutrient absorption, it becomes necessary to introduce grasses originated in tropical or subtropical regions. It has been reported that bahiagrass is recommended in the orchards of Taiwan. The grass becomes dormant from December to April in Japan. There is no problem of rhizosphere temperature as affected by the grass during the period from late March to April and the competition is not serious. The grass grows vigorously in summer. Herbicide treatments will be necessary. But the amount of herbicide for bahia grass control can be reduced to about one third compared with the miscellaneous weed control. In the future, growth retardants for bahiagrass might be developed and applied by overhead sprinkler system. Bahiagrass is weak at germination and is overcome by other species. So at present investigations are focussed on how to establish the species being dominant in the citrus orchards. Less