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Container experiments were carried out to study the effect of irrigation interval on root development, yield and water use efficiency for chile pepper. Each containers has a size of 31 x 15 x 60 cm with one transparent side for the visual view of the root development. Sandy clay loam soil was packed in each container to a 50 cm height. One seedling of chile pepper (Takano tsu me) was transplanted in the middle of each container on the 15th of February, 2005. Three irrigation intervals, (1, 3 and 5 day) with four replications were investigated. The soil water content in each container was kept at field capacity by compensating the loss in weight by adding water. The results indicated that increasing the water supply caused increases in the root biomass. The 1-day irrigation interval produced the highest root biomass while the 5-day resulted in the least root biomass. The 3-day irrigation interval showed remarkable roots development in the bottom of the containers, resulting in 12 % water saving compared to other treatments. The increasing in the irrigation interval induced an increase in the xylem water potential but it caused a reduction in leaf growth. Generally, the proper irrigation interval increases the plant water stress tolerance by developing the root in lower layers where high soil moisture content is present.

greenhouse experiment was conducted at Japan International Research Center for Agriculture Science (JIRCAS), Okinawa Subtropical Station, Ishigaki, Japan with three multiple water application and two single water applications to study the effects of them on tomato yield, soil water content and water use efficiency. Multiple water application is a technique use to add the required amount of water during irrigation in multiple equal parts a day instead of one complete set (single water application) during the irrigation event. The multiple water application treatments were the day time (DT), day–night time (DNT) and night time (NT) while the single water application treatments were morning time (MT) and evening time (ET). In multiple water irrigation treatments the water was added to the soil into three equal parts. The supplied irrigation water was the same for all treatments and gradually increased with plant age to cover the crop water requirement during the growing season. The results revealed that multiple water application increased tomato yield by 5% over the highest yield of single water application. The DT treatment increased tomato yield by 5% and 15% compared to ET and MT treatments, respectively. For multiple water application, the DT was the best irrigation timing because it increases the tomato yield by 8% and 12% compared to DNT and NT, respectively. ET irrigation was better than MT irrigation for single water application. Multiple water application led to an increased in soil water content compared to single water application. By applying the same amount of water for all treatments, the DT treatment increased water use efficiency by 5–15% compared to ET and MT treatments of single water application. In conclusion, multiple water application is better than single water application and by choosing the proper irrigation timing, higher tomato yield resulting from efficient water management can be obtained.

Two experiments were carried-out to study the effect of irrigation frequency and timing on root developments, tomato yield (var. First power) and soil water content at JIRCAS Okinawa Subtropical Station, Ishigaki, Japan. The first experiment was conducted in root containers (31 x 15 x 60 cm) with one transparent side for visual viewing of the root development. Sandy clay loam soil mixed with CaCO3 and P2O5 fertilizers was packed in the containers to 50 cm height with bulk density of 1.5 g/cm3. Three irrigation frequencies, 1, 3 and 5 days were investigated. The soil water content in the containers was kept at field capacity by compensating the loss in weight by adding water. The second experiment was conducted in a greenhouse with two irrigation frequencies, 1 and 3 days and three irrigation timings, early morning (8:00h), afternoon (14:00h) and night (20:00h). Soil water content at 0-60 cm and soil temperature at 15 cm depth were measured at 15 cm distance far from dripper by installing TDR sensors and thermocouples, respectively. The supplied amount of water was the same for all irrigation frequencies and gradually increased to cover the crop water requirements during each growing stage. The root containers results indicated that increasing water supply increased the root development and root biomass. The 1-day irrigation frequency produced the highest root biomass while the least root biomass was obtained from the 5-days irrigation frequency, indicating that water stress promoted the development of root system in the deeper layer where available soil moisture content was higher than the top layers. The 5-days irrigation frequency saved 18% and 12 % of water at early growth stage compared to 1 and 3 days frequencies. The results of greenhouse experiment showed that the best irrigation frequency was 3- days. The average yield in 3-days frequency was 70 ton/ha while 63 ton/ha in 1-day frequency. The effect of irrigation timing varied with irrigation frequency. For 3-days frequency, irrigation at early morning was better than afternoon and night irrigations. The average yield for irrigation at early morning was increased by 15% and 14% than irrigation at afternoon and night, respectively. For 1-day frequency irrigation at night increased the yield by 11% and 3% than irrigation at early morning and afternoon correspondingly. The lowest soil water content and soil temperature were displayed by the treatment, which produced the highest yield. With the same amount of water, the early morning irrigation after every 3-days increased tomato yield by 11- 20 % compared to night and early morning irrigation of 1-day frequency. A similar increase in water use efficiency in the early morning irrigation every 3-days was also recorded. Therefore, a selection of the proper irrigation frequency and timing led to a higher yield and high water use efficiency.

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Cultivating sandy soil is a promising solution to overcome the fight against hunger especially in the developing countries. The main problems of sandy soil are water and nutrients deficiency. A containers experiment was carried out to study the enhancement of water productivity and crop yield of sandy soils treated with clay. The container size was 31×15×60 cm with one transparent side for visual viewing of the root development beside growth characteristics. The soil with bulk density of 1.5 g/cm3 mixed with CaCO3 and P2O5 fertilizers was packed in the containers to 50 cm height. Three treatments: control, overlay and incorporation with four replicates were studied. The control treatment was only sandy soil, 4% by weight of clay was overlaid on the surface of sandy soil to constitute the overlay treatment (5.6 kg soil with 21.4% clay overlay on 28.4 kg sandy soil with 93% sand) while the same percentage of clay was incorporated with the upper 20 cm of sandy soil to represent the incorporation treatment. All the treatments received the same amount of irrigation water and fertilizers during the growing stage. The results indicate that the leaf area in cucumber and stem length, stem diameter and number of leaves in maize were increased in the treatments treated with clay. About 2.5 times of yield was obtained from those treatments compared to control. Roots grew intensively in the layers treated with clay. The incorporation treatment retained higher amount of water compared to control but with small differences compared to overlay treatment. The water use efficiency and water saving is highly increased by clay application and about 45%–64% of irrigation water can be saved compared with control.

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