Potential and actual evapotranspiration of Satsuma orange orchard in Aichi Prefecture

Abstract

During the years 1961-1962, the rate of the potential evapotranspiration in Satsuma orange trees (Citrus unshiu MARCOVITCH) has been determined by lysimeter method at Anjo, and the values obtained were compared with the values computed by THORNTHWAITE'S formula.
On the other hand, the actual evapotranspiration (consumptive use of water) in an orchard of Satsuma orange has been evaluated by “water balance sheet method” in the south region of Chita Peninsula.
1. Potential evapotranspiration; The values measured by lysimeter and the values computed by THORNTHWAITE'S method are shown in Table 1. Annual total of the former values was about 100mm higher than that of the latter.
2. In order to evaluate the potential evapotranspiration of mature citrus orchards, “Crown volume ratio” (tree crown volume per planted ground area ratio)was determined. This index of young trees in lysimeter experiment was 20% lower than the value measured in the mature citrus groves (30 year's old). Assuming that the evapotranspiration becomes greater in proportion to the increase in “Crown volume ratio” under the field condition, the annual total value of potential evapotranspiration becomes about 1200mm. It seems that this is the critical value of evapotranspiration from the mature citrus groves which have dense foliage, and deep root system.
3. Actual evapotranspiration; It was calculated as follows; U=P.W.L.+R outgo of profile water loss effective precipitation water (deficit of water) (income of water)
where U is consumptive use (actual evapotranspiration), P. W. L. is total moisture loss from soil profile, and this was estimated by soil weighing method.
The values calculated by this equation were compared with open pan evaporation and the values calculated by BLANEY-CRIDDLE'S formula.
The coefficients of BLANEY-CRIDDLE'S formula and the proportional coefficients of open pan evaporation were estimated as follows; a) Jun. -Oct. U=0.5F or U=0.8E b) Nov. -May U=0.4F or U=0.6E
where F is BLANEY-CRIDDLE'S function and E is open pan evaporation.
The seasonal change of the computed values for actual evapotranspiration is shown in Table 2.
4. Conclusion; It may be concluded from these investigations that the potential evapotranspiration of the vegetation which have dense foliage of the mature Satsuma orange groves and holds moisture in field capacity is 7mm/day during the season of great demand for moisture, but actual evapotranspiration is expected to be between 5-6mm/day under the wet condition of soil profile and 3-4mm/day under its relatively dry condition at the time of maximum moisture use.