Session 5. Subsurface Drip Irrigation I
Energy and Water Balances for Surface and Subsurface Drip Irrigated Corn
Steven R. Evett, Terry A. Howell, and Arland D. Schneider
Drip irrigation using buried emitters has the potential to save irrigation water by reducing soil surface wetting and thus reducing evaporation (E). However, measurement of evapotranspiration (ET) for different combinations of emitter depth and cropping systems can become onerous. We modified a mechanistic ET model, ENWATBAL, to simulate irrigation with drip emitters at any depth and modeled energy and water balance components for corn (Zeamays L., cv. PIO 3245) grown on the Pullman clay loam soil at Bushland, TX using emitters at the surface and at 0.15- and 0.30-m depths. Irrigation was daily and was scheduled to replace crop water use as measured in the field by neutron scattering. Modeled transpiration was essentially equal for all emitter depths (428 mm over 114 days from emergence to well past maximum leaf area index [LAI]) but evaporation was 51 mm and 81 mm less for 15- and 30-cm deep emitters compared with surface emitters. Predicted drainage was slight (6-, 8- and 12-mm for surface, and 0.15- and 0.30-m deep emitters, respectively), but comparisons of predicted and measured soil water profiles at season's end showed that deep drainage of over 150 mm of water may have occurred. There were minor differences in soil heat flux between the treatments because soil heat flux was a relatively minor component of the energy balance. For surface emitters, net radiation was much greater and sensible heat flux was smaller than for subsurface emitters until LAI increased past 4.2 midway through the season. Thus, almost all of the differences in ET occurred during the period of partial canopy cover. Differences in energy balance components between treatments were minor after day of year 220. The study showed that water savings of up to 10% of seasonal precipitation plus irrigation could be achieved using 30-cm deep emitters.
Keywords: Buried emitter, Evaporation, Transpiration, Corn, Model, Energy Balance, Water Balance
Abstract taken from paper found on pages 135 to 140 in Proceedings of 5th International Microirrigation Congress, April 2-6, 1995, Orlando, Florida. American Society of Agricultural Engineers, 2950 Niles Road, St. Joseph, Michigan 49085-9659, USA. Phone: 616-429-0300 FAX: 616-429-3852 EMAIL: HQ@ASAE.ORG
Impact of Bed Location on the Operation of Subsurface Drip Irrigation Systems
J. E. Ayars, C. J. Phene, R. A. Schoneman, B. Meso, F. Dale, J. Penland
Use of subsurface drip irrigation requires the establishment of a consistent row spacing for all crops in the rotation. If this practice is not followed, the drip lateral position will vary from being centered under the bed and row to being located under the furrow. Tomato and cotton yields and salinity distributions in the top 0.45 m of the soil were studied relative to the position of a subsurface drip irrigation lateral under the crop bed. The effect of lateral depth and placement on damage to the drip lateral was also studied for five types of drip tubing. The results demonstrated that the yields were not affected when the drip tubing was not centered under the bed. The presence of groundwater at a depth of 1.5 m probably affected this result. The salinity distribution demonstrated that the salts were moved to below the plant row as the lateral position shifted from the center of the bed to the edge of the bed. The incidence of mechanical damage increased as the lateral line moved from the center of the bed to the edge of the bed. In one instance over 30 m of drip tubing were dug up and had to be replaced.
Keywords: Subsurface drip irrigation, Lateral depth, Tomato, Cotton, Lateral spacing, Drip irrigation
Abstract taken from paper found on pages 141 to 146 in Proceedings of 5th International Microirrigation Congress, April 2-6, 1995, Orlando, Florida. American Society of Agricultural Engineers, 2950 Niles Road, St. Joseph, Michigan 49085-9659, USA. Phone: 616-429-0300 FAX: 616-429-3852 EMAIL: HQ@ASAE.ORG
Evapotranspiration, Fertility Management for Subsurface Drip Acala and Pima Cotton
R. B. Hutmacher, C. J. Phene, K. R. Davis, S. S. Vail, T. A. Kerby, M. Peters, C. A. Hawk, M. Keeley, D. A. Clark, D. Ballard, N. Hudson
A three-year study was conducted in a clay loam soil in the San Joaquin Valley of California to identify crop evapotranspiration (ETc) and growth and yield responses of Acala and Pima cotton varieties to a range of deficit subsurface drip irrigation (SDI) treatments. SDI laterals were placed 1.52 m apart, 0.45 m deep, with emitters 0.76 m apart. Treatments differed in the amount of water applied (60% to 100% of a conservative crop coefficient) and the duration and timing of deficit irrigation. All treatments received full irrigation through early square development (late June), with deficit treatments imposed during flowering and boll-filling. Lint yields were high (greater than 1900 kg ha-1) in all treatments in the first two years of the study, and moderate (less than 1750 kg ha-1) in the third year, with little reduction in lint yield in moderate deficit irrigation treatments. All treatments utilized substantial (grater that 200 mm) stored soil water in addition to irrigation water, resulting in ETc ranging from 575 mm to over 850 mm across treatments and years. Peak yields were achieved with 700 to 800 mm ETc. Nutrient uptake and plant water relations under deficit SDI were monitored according to growth stage. Deficit irrigation and a conservative crop coefficient proved effective in managing crop vegetative growth and achieving high yields.
Keywords: Evapotranspiration, Fertility, Deficit Irrigation, Subsurface Drip, Cotton
Abstract taken from paper found on pages 147 to 154 in Proceedings of 5th International Microirrigation Congress, April 2-6, 1995, Orlando, Florida. American Society of Agricultural Engineers, 2950 Niles Road, St. Joseph, Michigan 49085-9659, USA. Phone: 616-429-0300 FAX: 616-429-3852 EMAIL: HQ@ASAE.ORG
Potential of Subsurface Drip Irrigation for Management of Nitrate in Wastewater
C. J. Phene and R. Ruskin
Annual increases of food demand forecasts for various regions of the world range from 2.3% (East and South Asia) to 3.8% (West Asia and North Africa). Even when taking into account the potential production of rain-fed agriculture, the irrigated agricultural production sector will need to increase its productivity by 3 to 4% per annum. Secondary and tertiary treated domestic wastewaters (WW) are being used more and more for irrigation of field crops, landscape, groundwater recharge and other applications. However, the use of treated WW for irrigation is subject to major concerns because of the potential nitrate contamination of domestic water supplies possibly resulting in the occurrence of methemoglobinemia. In California, only 18% of the 5 billion cubic meters of generated WW is treated and returned to the state's fresh water system for incidental uses but only about 7% of it is used intentionally. The Water Management Research Laboratory (USDA-ARS-Fresno) developed a practical water and fertilizer efficient irrigation and management method which minimizes and sometimes even eliminates the downward movement of soluble nitrate-N below the root zone of field crops. The method known as deep high frequency subsurface drip irrigation (SDI) achieved minimum leaching when four conditions were satisfied: (1) irrigation events are short and frequent and designed to replace crop water uptake as closely as possible (no leaching fraction); (2) nitrogen is applied with the water through the SDI system at a rate equivalent to the uptake rate of the crop less the amount mineralized from the soil; (3) the crop is deep rooted; and (4) the shallow water table is at least 2.0 m from the soil surface. Results obtained for a ten year period with irrigated field crops demonstrate the potential of the SDI method for minimizing non-point source agricultural pollution with NO3-N. The SCI method also shows some unique and economical potential for safely irrigating field crops with treated WW. In addition to the controlled movement of NO3-N to the ground water, the mere fact that the treated WW does not come to the soil surface adds another safety dimension to the handling of a potentially hazardous material. In locations where year around cropping is possible, continuous disposal could be carried out without requiring major storage facilities. However, during the winter months when evapotranspiration (ET) is low, some reservoir might be required to store the excess WW not evapotranspired by the crop. The objectives of this paper are to present and discuss the design and operation of SDI systems, their physical characteristics, and research results defining soil water, nitrate-N and deep rootzone profiles obtained when deep SDI systems are used. The authors will relate how this method can be adapted for irrigation with treated WW.
Keywords: Reuse, Water use, Leaching, Treated Water
Abstract taken from paper found on pages 155 to 167 in Proceedings of 5th International Microirrigation Congress, April 2-6, 1995, Orlando, Florida. American Society of Agricultural Engineers, 2950 Niles Road, St. Joseph, Michigan 49085-9659, USA. Phone: 616-429-0300 FAX: 616-429-3852 EMAIL: HQ@ASAE.ORG
Resource Conservation and Preservation Through a New Subsurface Irrigation System
H. K. Barth
A subsurface microirrigation system was modified to include three innovative elements:
1) a new design of the lateral hoses preventing the penetration of roots into the external water outlets and the blockage by soil particles,
2) an impermeable polyethylene foil placed below the lateral pipes which prevents water loss through deep percolation especially in sandy substrates, and
3) special installation equipment consisting in a v-shaped device which releases the foil and pipe simultaneously into the soil without disturbance of the natural soil profile.
The experience from several years of operation have proved those new elements to be highly effective. Compared to other irrigation methods, the irrigation efficiency was outstanding. Minimum maintenance requirement and a long life span are additional positive characteristics of the system. The beneficial outcomes give reason for an optimistic appraisal of strategies for sustainable irrigated agriculture.
Keywords: Subsurface irrigation, water savings, resource conservation, productivity, socio-economic benefits
Abstract taken from paper found on pages 168 to 174 in Proceedings of 5th International Microirrigation Congress, April 2-6, 1995, Orlando, Florida. American Society of Agricultural Engineers, 2950 Niles Road, St. Joseph, Michigan 49085-9659, USA. Phone: 616-429-0300 FAX: 616-429-3852 EMAIL: HQ@ASAE.ORG