1994 Volume 69 Pages 49-54
The main aim of land evaluation is to assess the capability of land resources in relation to particular land uses referring to use on a sustained basis. The potential productivity of soil-plant systems which are possible to introduce in a land area under consideration is important as a general measure of land evaluation. A model combining agro-climatic approaches, analysis on soil water dynamics, and crop water use was introduced successfully to predict the potential and rainfed production of grassland ecosystems in north eastern Hokkaido. The model output, i.e. rainfed production of harvesting grassland in this area, agreed well when the water requirement of grasses was assumed at 400g g-1. This approach was effective to compare benefits of several alternatives in management practices and to give long-term predictions based on the limted information provided by short-term experiments. Data requirements to use this model include climatic items, suth as temperature, reinfall, relative humidity, and sunshine hours, hydrophysical properties of soils, such as water content vs. suction and unsaturated hydralic conductivity vs. suction curves, and water use characteristics of grasses. These physical characteristics of soils and soil-plant systems are indispensable to predict the nutrient limited production of plants, to analyze the dynamics of energy and materials through agro-ecological systems, and assess their impacts to hydrosphere and atmosphere in the context of environmental issues. The importance of soil physical properties and physical approaches in the quantitative land evaluation will grow bigger and bigger in the future.