Impact of Irrigation Water Stability on On-farm Water Distribution in a Paddy Field

Abstract

In order to clarify how the lot-management water requirement (LWR) and the delivery water requirement (DWR), which are regarded as independent components the paddy water requirement design of Japan, change, vary and correlate depending on water source stability water distribution in two irrigation areas of gravity-continuous irrigation (GCI) in the Kokai River basin and pumping-intermittent irrigation (PII) in the Kinu River basin was studied. LWR and DWR as well as applied water in the two areas both of which were divided into upper and lower blocks were surveyed once in two weeks for two irrigation seasons. The following findings were obtained: 1) The ratio of water effectively stored in paddy plots was rather less in PII area and the lower block of each area where less water was available. 2) Under the unstable water distribution condition farmers in the upper block tended to take excessive water, thus resulting in insufficiency and unstableness of water in the lower block. 3) The two water requirements of LWR and DWR are not independent; the distributed water in a paddy block was first diverted for storing on paddy plot and LWR, and the rest appeared at the tail-end of ditch as DWR.