Diversity of soil moisture movement in growing non-rice crops on paddy based land of tropical area and its analysis: study on diversified crop water requirements in the Philippines (II)

摘要

Diversity and complexity of soil moisture movement give difficulties of determining the effective soil layer (ESL) in applying soil moisture depletion method for non-rice crops in paddy based land. This paper aims at analyzing the reasons of these diversity and complexity based on the data of total 16 crops in the Philippines. Firstly, features of soil moisture movement were shown with changes of total potential gradients, and classified into three types. Furthermore, the conditions having appearance of three types were identified. Secondly, a mathematical model was made to quantify root water absorption ratios and analyze the reasons. Finally, typical example (s) of each type was analyzed by the model, and the appearance conditions of diversity and complexity were studied. The results indicated that (1) the diversity and complexity are caused by appearance of the maximum root water absorption ratio at the subsurface soil layer under high evaporative demand and by smallness of supplemental flux for the absorbed water due to low permeable soils, and (2) the difference in diversity and complexity is controlled by appearance and magnitude of the maximum absorption.