Effect of drip tape placement depth and irrigation level on yield of potato

Abstract

Subsurface drip irrigation (SDI) is the most advanced method of irrigation, which enables the application of the small amounts of water to the soil through the drippers placed below the soil surface. One of the most commonly discussed aspects of SDI system is installation depth of drip lateral. Determining the appropriate depth of installation involves consideration of soil structure, texture, and crop's root development pattern. Site-wise and crop-wise variations of these parameters preclude the possibility of framing general recommendations for installation depths of SDI system. An experiment was conducted on potato (var. Kufri Anand) during October–February for 3 years (2002–2003, 2003–2004 and 2004–2005) to study the effect of depth of placement of drip tape and different levels of irrigation application on potato yield. Drip tapes were buried manually in the middle of different ridges. Tests for uniformity of water application through the SDI system were carried out in the month of October every year. Three different irrigation levels of 60, 80 and 100% of the crop evapotranspiration and five depths of placement of drip tape namely, 0.0, 5.0, 10.0, 15.0 and 20.0 cm were maintained in the study. The coefficient of variation (CV) of flow rates was found 0.046, 0.047 and 0.064 during 2002–2003, 2003–2004 and 2004–2005, respectively. The low CV indicated good performance of the SDI system throughout the cropping season. The values of statistical uniformity (SU) and distribution uniformity (DU) were more than 92.0% during all the three cropping seasons. Soil water distribution at different growth stages of potato under different depths of placement of drip tape for varying irrigation levels was monitored. When drip tape was placed at surface and buried at 5.0 cm soil depth, upward movement of water takes place, 21.5% soil water content was found throughout the crop season of potato. When drip tape was buried 10.0, 15.0 and 20.0 cm below the surface, upward water movement due to capillary forces was not sufficient and soil surface remained relatively dry.

The maximum yield was recorded when drip tape was buried at 10.0 cm during 2002–2003 and 2004–2005 and at 15.0 cm during 2003–2004 that was followed by drip tape placement at 20.0, 10.0 and 5.0 cm depths in 2002–2003 to 2004–2005, respectively. Treatment 0.6T4 gave maximum IWUE of 2.07, 2.13 and 2.05 t ha⁻¹ cm⁻¹ during 2002–2003, 2003–2004 and 2004–2005, respectively. The highest benefit cost ratio of 1.7 was obtained for treatment T3. Lowest benefit–cost ratio of 0.9 was found for treatment 0.6T5. The cost incurred for the installation of drip tape at successively higher depths, increases the annual cost of production. The placement depth of drip tape significantly affected potato yield. Maximum yield was obtained by applying the 100% of the crop evapotranspiration (23.6 cm of irrigation water) and by placing the drip tape at 10.0 cm depth. In the sandy loam soil at the experimental site, the gravity force predominated over the capillary force causing a greater downward movement of water. Therefore, shallow depth of placement of drip tape (10.0 cm) was recommended in potato crop to get higher yield. Appropriate depth of placement of drip tape however, will differ with crop and the change in soil type.

Introduction

India would need to produce over 400 million tonnes of food grain from gradually diminishing per capita availability of land and water in order to fulfill the requirements of population of about 1.5 billion by the year 2020. With increasing demands on limited water resources and the need to minimize adverse environmental consequences of irrigation, drip irrigation technology will undoubtedly play an important role in the future in the Indian agriculture. It provides many unique agronomic, water and energy conservation benefits that address many of the challenges facing irrigated agriculture. Consequently, the use of drip irrigation is rapidly increasing around the world.

Drip irrigation system consists of drippers, which are either buried or placed on the soil surface for discharging water at a controlled rate. All micro irrigation systems have the potential to be very efficient in irrigation water conveyance, control and application. An irrigation system should apply water uniformly so that each part of the irrigated area receives same amount of water. Insufficient water leads to high soil moisture tension, plant stress and reduced crop yields. Excess water may also reduce crop yields below potential levels due to leaching of applied nutrients, increased disease incidence or failure to stimulate growth of the commercially valuable parts of the plant (Solomon, 1993).

Subsurface drip irrigation (SDI) is the most advanced method of irrigation, which enables the application of the small amounts of water to the soil through the drippers placed below the soil surface with discharge rates generally in the same range as surface drip irrigation (ASAE Std., 1999). SDI offers many advantages over the surface drip irrigation such as reduction in evaporation and deep percolation losses and elimination of surface runoff (Camp, 1998). Water infiltration in the SDI takes place in the region directly around the dripper, which is small compared with the total soil volume of irrigated field. A subsurface dripper usually forms a small cavity around it into which water can freely flow (Shani and Or, 1995). Uptake of water by plant roots causes soil drying and subsequent increased soil water tension. Selected drippers discharge should not exceed the root uptake rate (Clothier and Green, 1994, Clothier and Green, 1997, Lazarovitch, 2001).

Application of uniform and sufficient water to seed for good crop establishment is one of the most challenging issues of SDI. Establishment of crop in SDI relies on unsaturated water movement from the buried source to seed. The process is therefore affected by distance from water source to seed, evaporative demand and hydraulic conductivity, which is dependent on soil texture, structure and antecedent water content. One of the most commonly discussed aspects of SDI system is installation depth of drip lateral. Determining the appropriate depth of installation of drip laterals requires consideration of soil structure, texture and crop's root development pattern that hinders in providing general recommendations for installation depths of SDI systems (Burt and Styles, 1994).

Solomon (1993) reported that in SDI, irrigation water and injected fertilizers are supplied directly to the roots of crop. This is specially advantageous in case of nutrients that have low mobility into soil. In SDI, top 20.0 cm of soil have lower soil water content when laterals are buried at 45.0 cm soil depth, resulting in reduced evaporation (Phene et al., 1983, Solomon, 1993). A relatively dry soil permitted farm equipment movement during the whole cropping season and eliminated weed growth (Schwankl et al., 1990). SDI is also not exposed to sun and extreme weather condition ensuring a longer life of the system. Shani et al. (1996) mentioned that the water discharge rate from the SDI drippers would have to be controlled according to the soil hydraulic conductivity. Ruskin (2000) reported that SDI system could be used to apply water in small amounts and at higher frequency. He achieved a saving of 46% of water in comparison to surface drip in medium and heavy textured soil in which the water movement occurred mainly due to capillary forces. Lamm and Trooien (2003) found that corn yield was the highest under SDI at irrigation level of 75% crop evapotranspiration. Phene et al. (1992) also studied the environmental impact of SDI system in clay loam soil when drip tubes were placed at 45.0 cm below the soil surface. It was observed that soil water remained at the root zone for utilization of plants and was not lost due to deep percolation.

The uniformity of water application from a SDI system is affected both by the water pressure distribution in the pipe network and by the hydraulic properties of the drippers used. Dripper flow rate depends on its hydraulic properties, its design and water temperature. A major concern with SDI is evaluation of its performance and measurement of uniformity parameters of its discharge. The performance of the SDI system should be quantified in relation to its design, management, operation and efficient use of water. Quantification allows the users to determine and control the dripper discharge, amount and timings of application of irrigation water so that the crop water requirements are met in a planned and effective manner (Burt et al., 1997, Camp et al., 1997, Ayars et al., 1999).

Estimation of uniformity coefficient for surface drip irrigation is straightforward but it is difficult in SDI system in which the laterals are buried below the soil surface. Magwenzi (2001) found the statistical uniformity (SU) and the distribution uniformity (DU) varying from 89.0 to 93.0% and 85.0 to 92.0%, respectively, for drip tapes discharging at 1.6 Lph and buried at 15.0–20.0 cm below the sugarcane set at a spacing of 0.92 m. The performance of the SDI system, overhead, center pivot and surface drip were evaluated by Reinders (2001) for sugar growing areas of South Africa. DU and SU of SDI was found 68.0 and 74.0%, respectively. Various studies in the past have rated most of the SDI systems as excellent on the basis of their performance (Ayars et al., 1999, Magwenzi, 2001). Measurable indices of the degree of uniformity include CV (Wu, 1997), DU (Kruse, 1978) and SU (Bralts et al., 1981).

Potato (Solanum tuberosum) is an important crop of India with a production of 25.0 million tonnes (1 tonne = 1000 kg) from 1.34 million hectare area. India produces almost 13% of world's vegetable output occupying fifth rank in potato production. The average yield of potato in India is 19.0 t ha⁻¹, which is much below the potential productivity (FAO, 1998). Potato can be grown in all soil types but it prefers well-drained sandy loam soil. Potato is largely grown in cool regions where mean temperature does not normally exceed 18 °C. Optimum temperature for potato growth and development ranges between 15 and 25 °C. Potato is conventionally grown through vegetative reproduction of its tuber (Kashyap and Panda, 2003). Previous research shows that the yield and quality of potatoes improved through drip irrigation (Yuan et al., 2003, Onder et al., 2005, Kaur et al., 2005). The potato crop evapotranspiration vary from 30.0 to 70.0 cm, depending on the environment and crop growth stages (Shock and Feibert, 2000). Potato has a shallow root zone and has low tolerance for water stress (Schapendonk et al., 1989, Van Loon, 1981). Drought severity, timing and duration of water stress during the different growth stages of potato crop influences the crop yield. King et al. (2003) studied the effect of two levels of irrigation 80 and 60% of water requirement on yield of potato (var. Russet Burbank tubers). The 3 weeks water stress intervals was maintained during early, mid and late bulking stage of crop. They reported that the total potato yield reduced mainly when deficit irrigation was applied during early mid and mid late bulking, regardless of water stress intensity. However, in some circumstances, potatoes can tolerate limited deficit irrigation before tuber set without significant reductions in external and internal tuber quality (Shock et al., 1992). Expected potato yield of 79% and relative water use efficiency of 1.06 was obtained when 25% deficit of evapotranspiration was prevailed for the whole season of potato (Kirda, 1982).

The present experiment was conducted for the first time in India to study the influence of subsurface drip tape on the yield of potato. Drip manufacturers in India do not produce drip tape. For the reported experiment, therefore, drip tape was imported from T-tape systems, Australia. The objectives of this study were (1) to evaluate the performance of SDI system, (2) to study the effect of different levels of application of irrigation water on yield of potato and (3) to determine the optimal depth of placement of drip tape on the basis of shape and position of the wetting zone beneath it.