2022 年 32 巻 3 号 p. 90
We have presented a new scheme, “optimized irrigation”, in which irrigation depth is determined such that net income considering the price of water and weather forecasts during each interval is maximized using WASH_1D/2D which are numerical simulation models of water flow and solute transport in soils and crop growth. To evaluate whether the optimized irrigation is also able to restrict salinity stress and avoid salinization without any intentional leaching, we carried out an irrigation experiment.
Mungbean (Vigna radiata L.) was grown in a greenhouse in Arid Land Research Center, Tottori University, using a drip irrigation system whose emitter distance was 20 cm and lateral spacing was 60 cm. Seeds were sown on May 18 below each emitter after leaching with more than 200 mm. Three treatments were established: 1) irrigation with fresh water (F), 2) irrigation with 1.5 g/L of NaCl solution (C), 3) irrigation with 1.5 g/L of NaCl solution and irrigation depth was determined with the proposed scheme (O). Treatments F and C were irrigated with automated irrigation systems using two tensiometers each installed below 10 cm. Each treatment had three replicates. After June 12, irrigation using the saline water started for treatments C and F. A 2.8 mm of leaching was carried out on July 2.
Treatment F received the largest amount owing to the largest transpiration rate without any stresses. Treatment C received the lowest amount because of low transpiration rate due to severe salinity stress. We compared net income under producer price of 0.9 $/kg, common miscellaneous costs at 50 $/ha, water price of fresh water at 0.2 $/m3 and that of saline water 0.1 $/m3. Treatment F gained the highest gross income owing to the largest yield (835 kg/ha). Treatment C gained the lowest income and yield (448 kg/ha) while treatment O gained the highest net income owing to lower cost for water than that for F, revealing the effectiveness of the proposed scheme.
