Until recently, chemical fertility of soil had genarally been the primary environmental factor limiting crop productivity of upland farming in Japan. Now, however, with abundant fertilization, “physical fertility”,the degree to which the physical factors of the soil are suitable for optimum plant nutrition and root functioning, is becoming the major limiting factor along with the climatological factors. Therefore, the future development of high yield, upland farming will require a multidisciplinary, organic approach in order to assemble the best combinations among the plant’s genetic factors and the environmental factors, including the physical, chemical, and biological components. Some of the problems concerning plant nutrition and production ecology that must be solved with the par, ticitation of soil physicists are presented:
1)The alleviation of temperature stresses by the integrated management of soil, water, and nutrients.
2)The unified management of plant nutrients, of which nitrogen is the most important, and soil water for maximum economic yield and pollution control.
3)The expansion of the “living space” for the subterranean part of the plant------particularly in relation to protecting the most fertile, surface layer that is often disturbed by machinery.
4)The elimination of the rhizosphere stress through improvement of transport and metabolism within the soil.
Using a flowing solution technique, a giant wheat plant yielding more than 400 g. of grain was raised. This implies that a reduction of the rhizosphere stress below the “normal” level might be a key factor in a breakthrough in the yield limit of the current crop methods.
The moisture content of soil is an important factor in determining the productivity of plants. Many of the climatological models used in estimating plant yields are expressed in terms of a humidity index calculated from weather data, such as precipitation, air temperature and humidity, and solar radiation. The “Chikugo” model developed by the authors is presented as an example of the above. While this kind of model works well for large space and time scales, in order to accurately monitor soil moisture and estimate plant yields for smaller space and time scales, direct evaluation of soil moisture content is necessary. With that in mind, we will present a simple model to estimate soil moisture content on a daily basis from weather data. The model is based on a simple water balance in flat layered soil and is written as:
where dW is the change in soil moisture content, R is precipitation, Et is evapotranspiration, and Sp is surplus water. The terms Et and Sp are estimated from weather data on the basis of the moisture characteristics of the soil. When the values derived from the model were compared with actual soil moisture measurements, a very good correlation was obtained.
The AVRDC (Asian Vegetable Research and Development Center) soil science unit has developed a noncirculating hydroponics system which requires neither aeration, nor monitoring of pH, EC, temperature or nutrient level. Once the facility has been established, the only input required is the addition of nutrients once every two weeks. The composition of nutrient solution need not be changed for each crop. During the summer of 1986, soybean, green pepper, large-fruited tomato, melon and cucumber were all successfully grown. Yields of the latter three were 3.1kg (average fruit wt:130g), 2.34kg and 4.72kg per plant, respectively.
The authors summarized the biological factors involved in the formation of several kinds of soils in established grasslands and suggested the future course of the method of grassland establishment which was payed regard to the conservation of natural environment. The authors described mainly the effect of root system on the clay mineralogical characteristics as well as physical and chemical ones of some kinds of soils, and also described briefly the importance of the roots of grasses and legume, soil fauna and soil microbe as the biological factors involved in the formation of grassland soil. After discussing the classification and the problems of the methods of grassland establishment adopted in Japan recently, it was considered to be introduce Landscape EcologyM which studied the method of grassland establishment with attention to the conservation of natural environment and the beautiful landscape. And the authors suggested the ploughless method with a stumpcutter-bushcutter system as an ecological method of grassland establishment which would satisfy those needs.