James E. Ayars

Subsurface drip irrigation of row crops: a review of 15 years of research at the Water Management Research Laboratory

Abstract Use of subsurface drip irrigation (SDI) has progressed from being a novelty employed by researchers to an accepted method of irrigation of both perennial and annual crops. This paper reviews the SDI research conducted by scientists at the Water Management Research Laboratory over a period of 15 years. Data are presented for irrigation and fertilization management on tomato, cotton, sweet corn, alfalfa, and cantaloupe for both plot and field applications. Results from these studies demonstrated significant yield and water use efficiency increases in all crops. Use of high frequency irrigation resulted in reduced deep percolation and increased use of water from shallow ground water when crops were grown in high water table areas. Uniformity studies demonstrated that after 9 years of operation SDI uniformity was as good as at the time of installation if management procedures were followed to prevent root intrusion.

The resource potential of in-situ shallow ground water use in irrigated agriculture: a review

Shallow ground water is a resource that is routinely overlooked when water management alternatives are being considered in irrigated agriculture. Even though it has the potential to provide significant quantities of water for crop use under the proper conditions and management. Crop water use from shallow groundwater is affected by soil water flux, crop rooting characteristics, crop salt tolerance, presence of a drainage system, and irrigation system type and management. This paper reviews these factors in detail and presents data quantifying crop use from shallow ground, and describes the existing state of the art with regard to crop management in the presence of shallow ground water. The existing data are used to determine whether in-situ crop water use from shallow ground water is suitable for a given situation. The suggested methodology uses ratios of ground water electrical conductivity to the Maas–Hoffman yield loss threshold values, the day to plant maturity relative to plant growth period, and the maximum rooting depth relative to the nearly saturated zone. The review demonstrates that for in-situ use to be feasible there has to be good quality ground water relative to crop salt tolerance available for an extended period of time. Shallow ground water availability is one area that can be managed to some extent. Crop selection will be the primary determinant in the other ratios.

Long term use of saline water for irrigation.

Use of saline drainage water in irrigated agriculture, as a means of its disposal, was evaluated on a 60 ha site on the west side of the San Joaquin Valley. In the drip irrigation treatments, 50 to 59% of the irrigation water applied during the six-year rotation was saline with an ECw ranging from 7 to 8 dS/m, and containing 5 to 7 mg/L boron and 220 to 310 μg/L total selenium. Low salinity water with an ECw of 0.4 to 0.5 dS/m and B ≈ 0.4 mg/1 was used to irrigate the furrow plots from 1982 to 1985 after which a blend of good quality water and saline drainage water was used. A six-year rotation of cotton, cotton, cotton, wheat, sugar beet and cotton was used. While the cotton and sugar beet yields were not affected during the initial six years, the levels of boron (B) in the soil became quite high and were accumulated in plant tissue to near toxic levels. During the six year period, for treatments surface irrigated with saline drainage water or a blend of saline and low salinity water, the B concentration in the soil increased throughout the 1.5 m soil profile while the electrical conductivity (ECe) increased primarily in the upper l m of the profile. Increaszs in soil ECe during the entire rotation occurred on plots where minimal leaching was practiced. Potential problems with germination and seedling establishment associated with increased surface soil salinity were avoided by leaching with rainfall and low-salinity pre-plant irrigations of 150 mm or more. Accumulation of boron and selenium poses a major threat to the sustainability of agriculture if drainage volumes are to be reduced by using drainage water for irrigation. This is particularly true in areas where toxic materials (salt, boron, other toxic minor elements) cannot be removed from the irrigated area. Continual storage within the root zone of the cropped soil is not sustainable.

Characterizing ground water use by safflower using weighing lysimeters

Abstract Decades of irrigation on the west side of the San Joaquin Valley without sufficient drainage have created large areas where shallow ground water (

Crop coefficients for irrigating cotton in the presence of groundwater

A cotton crop coefficient was modified to account for the contribution of shallow groundwater to crop water use. The data used in the modification were developed using weighing column lysimeters. The percentage groundwater contribution to crop water use, expressed as a function of growing degree days for several salinities and two water table depths, was used in the regression analysis. Use of the modified coefficient was demonstrated by scheduling a subsurface drip irrigation system installed in an area with shallow saline groundwater. Use of the modified crop coefficient resulted in 25% of the cotton water requirement being extracted from shallow groundwater with a salinity of 5 dS m-1 without any adverse effects on vegetative plant growth and yield. Groundwater depth dropped from 1.2 to 2.2 m during the growing season.

Uptake of shallow groundwater by cotton: growth stage, groundwater salinity effects in column lysimeters

Abstract A 3-year column lysimeter experiment was conducted with cotton ( Gossypium hirsutum L.) to determine the influence of shallow groundwater salinity on groundwater uptake. Nonsaline (0.3 dS m −1 ) irrigation water was applied at 7-day intervals throughout the growing season, with the cotton allowed to use stored soil water and groundwater as root water uptake permitted. Groundwater salinities ranging from 0.3 dS m −1 electrical conductivity (EC w ) to 30.8 dS m −1 were evaluated. Water for leaching was applied following harvest each year in amounts adequate to produce a nonsaline soil profile at the beginning of each year. Equations were developed to describe relationships between day of year, growth stage or growing degree days and shallow groundwater uptake. Groundwater contributed about 30 to 42% of seasonal total evapotranspiration (ET) in treatments with groundwater salinity ≤ 20 dS m −1 but declined to 12 to 19% of total ET at higher salinity levels.

Subsurface drainage design and management in irrigated areas of Australia

Abstract. Subsurface drainage to protect irrigated cropping has been practised in some areas of Australia since the 1920s, and most irrigation districts have large land areas protected by some form of subsurface drainage. Across the irrigated areas, a broad spectrum of practices were developed that suited the conditions at the time of development. This paper assesses the performance of these subsurface drainage systems in terms of long-term sustainability of irrigated agriculture, based on the results of a detailed review of all the subsurface drainage systems in use in Australian irrigation areas. The long-term sustainability of irrigated agriculture depends upon controlling the salinity levels in the crop root zone and maintaining the ability to dispose of drainage water. This requires that subsurface drainage systems are efficient in terms of removing the minimum amount of water with the lowest salinity possible, given the existing conditions, while still maintaining crop productivity. Analysis of the current drainage system operation showed that many systems were draining greater volumes of water than designed for, leading to excessively high leaching fractions, and reduced irrigation water-use efficiency. The salt load removed by these systems was also often found to be far greater than the salt applied by irrigation, indicating a mining of stored salt. This is necessary from a salinised root zone but not if the salt is from below the root zone. The extra salt load above that required to maintain a salt balance in the root zone leads to increased difficulties in the disposal of the drainage water due to downstream impacts. Suggestions are discussed for adaptive management and new design considerations that may help make subsurface drainage more efficient, leading to reduced negative downstream effects and reduced costs of disposal.

Realizing the potential of integrated irrigation and drainage water management for meeting crop water requirements in semi-arid and arid areas

In situ use of ground water by plants is one optionbeing considered to reduce discharge of subsurfacedrainage water from irrigated agriculture. Laboratory, lysimeter, and field studies havedemonstrated that crops can use significant quantitiesof water from shallow ground water. However, moststudies lack the data needed to include the crop wateruse into an integrated irrigation and drainage watermanagement system. This paper describes previousstudies which demonstrated the potential use of groundwater to support plant growth and the associatedlimitations. Included are results from three fieldstudies which demonstrated some of the managementtechniques needed to develop an integrated system. The field studies demonstrated that approximately 40to 45% of the water requirement for cotton can bederived from shallow saline ground water. Thatregulation of the outflow will result in increasinguse. Implementation of integrated management ofirrigation and subsurface drainage systems is a viableand sustainable alternative in the management ofsubsurface drainage water from arid and semi-aridareas only if soil salinity can be managed and if thesystem is profitable.

Managing irrigation and drainage systems in arid areas in the presence of shallow groundwater: case studies

Two field studies were conducted on the west side of the San Joaquin Valley of California to demonstrate the potential for integrated management of irrigation and drainage systems. The first study used a modified cotton crop coefficient to calculate the irrigation schedule controlling the operation of a subsurface drip system irrigating cotton in an area with saline groundwater at a depth of 1.5 m. Use of the coefficient resulted in 40% of the crop water requirement coming from the groundwater without a loss in lint yield. The second study evaluated the impact of the installation of controls on a subsurface drainage system installed on a 65 hectare field. As a result of the drainage controls, 140 mm less water was applied to the tomato crop without a yield loss. A smaller relative weight of tomatoes classified as limited use, was found in the areas with the water table closest to the soil surface.

Strategies for reducing subsurface drainage in irrigated agriculture through improved irrigation

The traditional approach ofinstalling subsurface drainage systems tosolve shallow ground water problems is notfeasible along the west side of the SanJoaquin Valley of California because of thelack of drain water disposal methods thatare economical, technically feasible, andenvironmentally friendly. Thus, optionssuch as drainage reduction through improvedirrigation and drain water reuse are beingexamined as methods for coping with thesubsurface drainage problem. This paperdiscusses options for reducing subsurfacedrainage through improved irrigationpractices. Options are discussed forimproving irrigation system design such asupgrading existing irrigation methods andconverting to systems with higher potentialirrigation efficiencies. Methods forimproving water management are alsopresented. Case studies on upgradingexisting systems or converting to otherirrigation methods are presented along with study results of the effect of variouspolicies on reducing subsurface drainage.