EFFECTS OF GROWING MEDIA AND WATER REGIMES ON GROWTH, YIELD AND WATER USE EFFICIENY OF SQUASH (CUCURBITA PEPO)

Field experiments were carried out, at the Agricultural Experimental Station Farm, College of Agriculture, King Saud University Located at Deerab, 50 km South of Riyadh, Saudi Arabia in tow seasons (2002 -2003). The treatments used were as follows: Three natural deposits applied at depth of 20 cm at three rates (0, 1.0 and 2.0%) and four irrigation levels (60, 80, 100 and 120% of ETo) using surface and subsurface drip irrigation. Results indicated that squash fruit yield was significantly increased with the increase in irrigation level, whereas WUE significantly increased then decreased at the highest irrigation level. The average yield increased by 11.66% in high irrigation level compared to moderate irrigation level, and decreased by 39.06% at the more stressed irrigation level. WUE increased by 7.58% at high irrigation level and decreased by 33.0% at stressed irrigation level. Types of clay deposits significantly affected fruit yields compared with the control. The yield increase was 12.78, 8.32 and 6.38% for Khulays, Dhruma and Rawdat clay deposits, respectively. The differences between surface and subsurface drip on fruit yields and WUE were also significant. Results indicated that moisture content of subsurface treated layer increased dramatically, while salts were accumulated at the surface and away from the emitters in subsurface drip irrigation. Intensive root proliferation is observed in the clay amended subsurface layer compared with non amended soil. The advantages of subsurface drip irrigation were related to the relative decrease in salt accumulation in the root zone area where the plant roots were active and water content was relatively higher. INTRODUCTION Field water management practices are the most influential factors affecting crop yield particularly in irrigated agriculture in arid and semiarid regions. Sandy soils are particularly critical for water management in irrigated agriculture because of their low water holding capacity and low clay contents. The productivity of these soils is limited by high infiltration rate, high evaporation, low fertility level, low water holding capacity and low organic matter content. Synthetic soil conditioners were used to alleviate some of these constrains (Choudhary et al., 1998; Al-Omran et al., 1987; Al-Harbi et al., 1999). Due to their high cost and insufficient longevity, the use of natural amendments could be a better alternative to improve the chemical and physical properties of these soils (Al-Omran et al., 2002 & 2004). The use of these deposits may increase the productivity, especially in the areas where these materials are available naturally in abundance and inexpensive (Abou-Gabal et al., 1990). The sustainable use of scarce water resources in Saudi Arabia is a priority for agricultural development. The pressure of using water in agriculture sector is increasing to create ways to improve water use efficiency and taking a full advantage of available water. Therefore, adoption of modern irrigation techniques is needed to be emphasized to increase water use efficiency. Drip irrigation is the most effective way to convey directly water and nutrients to plants and not only save water but also increases yields of vegetable crops (Tiwari et al., 1998a,b; Tiwari et al., 2003). Phene et al. (1991) studied the distribution of sweet corn roots as a function of drip placement and fertilization treatment. They reported differences between surface and subsurface drip irrigation on sweet corn rooting system in the top 45 cm. High root length density was observed below 30 cm in the subsurface drip irrigation than in the Proc. IS on Soilless Cult. and Hydroponics Ed: M. Urrestarazu Gavilán Acta Hort. 697 ISHS 2005 232 surface drip. Ibrahim, et al. (1987) reported high and intensive tomato root proliferation in the organic manure layer added as a thin subsurface layer in sandy soils. They added that the highest WUE of tomato was obtained from the subsurface application of manure under drip irrigation system. Recently, Bryla et al. (2003) reported that drip irrigation improved production and water use efficiency of faba bean in California using different levels of irrigation based on percentage of evapotranspiration. Ayars et al. (2001) reported from their studies on subsurface drip irrigation and furrow irrigation in the presence of shallow saline ground water that yield of the drip irrigated cotton improved during the 3-year study, while that of furrow irrigated cotton remained constant. Also, tomato yields were greater under drip irrigation than under furrow irrigation in the same study from the first year. Sammis (1980) found that, drip irrigation allows uniform delivery of water and nutrients directly to the plant root zone. This can increases N use efficiency over other irrigation methods (Miller et al.,1981). Lamm and Trooien (2003) reported that a successful application of subsurface drip irrigation for 10 years in Kansas, USA reduced the irrigation water use for corn by 35  55% compared with more traditional forms of irrigation. Thompson and Doerge (1996) found that soil water tension at 0.3 m depth should be maintained at 6 to 7 kPa for optimum yields of drip irrigated leaf lettuce. Also, Thompson and Doerge (1995) reported that under subsurface drip irrigation a target of soil water tension of no wetter than 6.5 kPa is appropriate for subsurface trickle irrigated Romain lettuce. Phene et al. (1987) reported that subsurface drip irrigation improved WUE of tomato plants. Therefore, the purpose of this study was to investigate the influence of irrigation levels and surface and subsurface drip irrigation on squash fruit yield, water use efficiency, water and salts distributions and rooting pattern in irrigated sandy calcareous soils amended with different rates of natural clay deposits. MATERIALS AND METHODS Field experiment was conducted at the College of Agricultural Research Station at Dirab, (2425' N, 4634' E), 50 km south of Riyadh, Saudi Arabia, during the months of AprilJune for two seasons (2002 and 2003). Selected properties of the soil and irrigation water were determined by the standard procedure (Page et al., 1982) are shown in Table 1. The soils are non saline, calcareous (CaCO3 ranges from 269 to 353 gKg soil) and sandy in texture, while irrigation water has high salt content (TDS=3300 mg/l) and moderate alkalinity (SAR=7.69). Natural clay deposits were collected from different regions in Saudi Arabia e.g western region (Khulays) and central region (Dhurma and Rawdat areas). Deposit samples were prepared by grinding and sieving through a 2mm sieve. Some physical and chemical characteristics of representative samples are presented in Table 2. The three amendments (Khulays, Dhurma and Rawdat) were applied in each row as a subsurface thin layer at a depth of 15 20 cm and at rates of 1 and 2% of the soil. The experimental layout was presented in (Fig. 1). It included surface (S) and sub-surface (SS) drip irrigation, with four irrigation levels at 60(T4), 80(T3), 100(T2), and 120% (T1) of the estimated crop evapotranspiration (ETo). The 30 m x 30 m field plot was divided into four equal subplots for the irrigation levels (T1, T2, T3, and T4). Surface and subsurface drip irrigations were installed in each half of the subplots, respectively. Drip tubing (GR type, 16 mm diameter) with 40 cm emitter spacing built in (delivering 4 Lhr) was used in the surface and the subsurface drip irrigation treatments. The experiment was laid out following the complete randomized block design with three replicates for each treatment (Fig. 1). Each treatment consists of 7 drippers (2.8 m tubing) and the distance between two rows was about 1 m. Squash (Cucurbita pepo cv. Mashael) seeds were sowed on April, 10, 2002 for the first season and April 1, 2003 for the second season with three seeds at each dripper. Irrigation through the surface drip tubing was commenced after planting in all treatments for the establishment. Uniform irrigation was continued on all treatments until the stand was established (one to two leaf stage), then subsurface drip irrigation was operated afterward for delivering irrigation water to the buried irrigation tubes. Uniform fertigation was used to deliver the fertilizer requirements using (N,P,K) liquid fertilizer in all treatments. The second season plantations were essentially commenced on the previous treatments at the same site. Nine soil samples were collected before irrigation from the root zone area on a grid bases (15 cm apart) around the dripper at three growth stages namely vegetative stage, flowering stage and at the end of the season. Samples were collected from the lower and higher amendment rate treatments and then water contents were determined by gravimetric method after oven drying at 105C. Salt