Richard A. Schoneman

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.

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.

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.

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.

Cotton response to nonuniform and varying depths of irrigation

Abstract A field experiment was conducted to evaluate the effect of nonuniform application of irrigation water at varying depths on deep percolation losses, crop water use and yield response of cotton. The experiment was conducted in the San Joaquin Valley of California using a linear move sprinkler system which had been modified to apply water at 3 different levels of uniformity and 2 different scale lengths. The effects of these application uniformities on cotton growth and yield were evaluated at 4 different average levels of water application (0.7, 0.9, 1.1, and 1.3 times crop evapotranspiration, et c). The leaf area index, plant height and total above-ground dry matter all exhibited a row-by-row response for the three lowest irrigation treatments. The seed cotton yields measured across rows did not follow the same pattern as the other plant parameters. Water applications far in excess of evapotranspiration often resulted in poor yields due to excess vegetative growth. In terms of above-ground total plant dry matter production, high water use efficiencies occurred with either short scale length or high application uniformities. Particularly in the 0.7 and 1.3 et c treatments, cotton yields and growth were greater in the more nonuniform treatments than in uniform treatments due to the adequate (not excess or deficit) irrigation occurring in some rows of the pattern.