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.
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