Blaine R. Hanson

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.

Response of garlic to irrigation water

The effect of irrigation frequency, irrigation water cutoff date, and amount of applied water on garlic yield was investigated. Project location was the west side of the San Joaquin Valley in California. Randomized plots replicated six times were used for the irrigation frequency and the cutoff experiments. Frequencies were one irrigation per week, one irrigation every 1.5 weeks, and one irrigation every 2 weeks. Cutoff dates were 12, 19, 25 May and 4 June. Sprinkler line-sources were used to develop relationships between garlic yield and applied water on sandy loam and clay loam. The highest yield occurred for the one irrigation per week treatment of the irrigation frequency experiment. The cutoff experiment showed highest yield for the 12 and May 12 cutoff dates. No yield response to applied water occurred for the line-source experiment in clay loam. Soil-moisture content data showed that garlic extracted soil-moisture deeper than 1.07 m to compensate for deficit irrigation. Garlic yield decreased linearly with applied water in sandy loam. The limited amount of stored soil-moisture in the sandy soil was insufficient to compensate for deficit irrigation. These results suggest that on sandy soil, weekly irrigations of an amount equal to the crop evapotranspiration plus losses due to irrigation inefficiencies should be applied. On fine-texture soil with the soil-moisture profile at field capacity in February, deficit irrigations can occur without reducing yield.

Estimating furrow infiltration

Abstract Furrow irrigation, the most common irrigation method in California, can be difficult to manage efficiently because of lack of quantitative information on infiltration rates. Conventional methods of measuring infiltration rates are not likely to be used on routine evaluations of furrow irrigation system. However, volume-balance simulation models of furrow irrigation, which estimate infiltration from water advance data, offer a potential for estimating infiltration in furrows. Six models were evaluated using detail data from 200 furrow evaluations. Results showed an inverse relationship between the exponent of the power advance equation and the exponent of the infiltration equation. This relationship tended to cause the models to greatly underestimate cumulative infiltration as the advance exponent approach unity. The models ability to predict system performance under different flow rates given an initial flow rate was also investigated.

Uniformity of Infiltrated Water Under a Low Energy Precision Application (LEPA) Irrigation System

ABSTRACT UNIFORMITY of infiltrated water of LEPA irrigation systems is not only affected by hydraulic losses, but also by the machine movement, the furrow check spacing, and the variability of soil infiltration rates, since water is ponded between dikes or checks along a furrow. We assessed the impact of these sources of nonuniformity using both machine movement characteristics measured during a field evaluation of a linear-move machine and soil infiltration measurements made over consecutive 1-m intervals during an unrelated project. Results showed that while the reported uniformity of the nozzle discharges may be 95%, the uniformity of infiltrated water may be between 80% to 85%. For small check spacings, uniformity was primarily affected by the machine movement, while for larger spacings, variability in the soil infiltration rate was the controlling factor. Results show need to consider all sources of nonuniformity of infiltrated water.

Crop Coefficients for Drip-irrigated Processing Tomatoes

Efficient management of drip irrigation systems requires reasonable estimates of crop nevapotranspiration (ET), normally calculated as the product of a crop coefficient and a reference crop nET. However, a review of literature revealed mid-season crop coefficients of processing tomatoes to nrange from 1.10 to 1.25. Thus a study was initiated to determine the crop ET and crop coefficients of nprocessing tomatoes under drip irrigation. Crop ET was determined for a four locations on the west nside of the San Joaquin Valley of California using the Bowen Ratio Energy Balance Method. Canopy ncoverage was also measured using a digital infrared camera. Results showed crop coefficients to nrange from about 0.2 at 10% canopy coverage to 1.09 for canopy coverage exceeding about 90%. A nrelationship between canopy coverage and crop coefficient was independent of site-specific nconditions (planting date, climate, cultural practices).

Response of Processing and Fresh-market Onions to Drip Irrigation

The response of yield to surface-and-subsurface drip irrigation was investigated for both nprocessing onions and fresh-market onions. Irrigation treatments consisted of water applications nranging fro 60% to 120% of a baseline amount for both irrigation methods. Data collected were napplied water, yield, soluble solids (processing onions), canopy coverage, canopy temperature, and nsoil moisture content. nResults showed a linear increase in total yield with increasing amounts of applied water for both nprocessing and fresh-market onions. However, for the fresh-market onions, little change in yield noccurred for the medium and repack grades. No differences in the yield-applied water relationships nwere found between surface-and-subsurface drip irrigation.

Effect of Subsurface Drip Irrigation on Processing Tomatoes Yield, Water Table Depth, and Soil Salinity

This study evaluated the potential of subsurface drip irrigation of processing tomatoes for nreducing subsurface drainage and controlling soil salinity, and for increasing farm profits in areas naffected by saline, shallow ground water. Subsurface drip irrigation systems were installed in three nfields of fine-textured, salt-affected soil along the west side of the San Joaquin Valley. No subsurface ndrainage systems were installed in these fields. Yield and quality of processing tomato of the drip nsystems were compared with sprinkler irrigation systems used in the remainder of the fields. nYield increases of 12.90 Mg/ha to 22.62 Mg/ha were found for the drip systems compared to the nsprinkler systems with similar amounts of applied water. Solids content of the drip-irrigated nprocessing tomato were acceptable. Response of water table levels during drip irrigation showed that nproperly managed drip systems could reduce percolation below the root zone. Yields of the drip nsystems were similar over a range of soil salinity levels in the soil profile.

Salinity Control with Drip Irrigation

Drip irrigation has the potential of increased yield under saline soil conditions. Factors affecting root zone soil salinity under drip irrigation include the salinity of the irrigation water, amount of applied water, soil hydraulic characteristics, placement of drip lines relative to plant rows, subsurface vs. surface drip lines, and under saline, shallow ground water conditions, the ground water depth and salinity. The salt pattern reflects the water flow patterns under drip irrigation. The key to profitable drip irrigation under saline conditions is adequate salinity control by leaching salts from the root zone. Under drip irrigation, highly concentrated leaching, called localized leaching, occurs near drip lines. Leaching decreases with horizontal distance from drip lines. Larger amounts of applied water increase the volume of leached soil near drip lines. Salts accumulate above subsurface drip lines, which requires rainfall or sprinkle irrigation for leaching. The water balance method of estimating leaching fractions is inappropriate for drip irrigation and underestimates the actual leaching fractions. Water applications equal to crop evapotranspiration provide adequate localized leaching.

Estimating Evapotranspiration of Fully-and Deficit-irrigated Alfalfa in Commercial Fields with the Eddy Covariance and Surface Renewal Methods

Evapotranspiration (ET) of fully irrigated and deficit irrigated (no irrigation in July, August, and September) was measured in four commercial alfalfa fields with the eddy covariance (EC) and surface renewal (SR) energy balance methods. Both EC and SR methods were used in the fully irrigated part of the fields, while the SR method only was used in the deficit irrigated part. Deficit irrigation reduced ET, but the amount of reduction was highly site specific. Good agreement was found between the EC and SR methods. However, patterns of the daily differences between the EC and SR methods differed between the four fields.

Crop Nitrate Availability and Nitrate Leaching under Micro-Irrigation for Different Fertigation Strategies

A drip-industry recommendation is to fertigate during the middle one third or one half of the nirrigation set. However, fertigation events occurring for short time periods are common, which npractice could affect crop nitrate availability and nitrate leaching below the root zone. The pattern of nfertilizers such as nitrate and urea around a drip line can depend of the duration of fertigation and the ntiming of the fertigation relative to the irrigation set time. Thus, a study was conducted to evaluate nnitrate distributions in the soil for various fertigation strategies, soil types, and methods of microirrigation. nResults showed that short fertigation events occurring near the beginning of an irrigation nevent can move much of the nitrate beyond the root zone and contribute to leaching. Short fertigation nevents at the end of the irrigation event leave much of the nitrate near the drip line. Fertigation nevents of longer duration distribute nitrate more uniformly throughout the root zone.