R. J. Hanks

Corn production as influenced by irrigation and salinity — Utah studies

SummaryThis paper reports the results of a two-year field study at Logan, Utah which was one of a series of similar experiments carried out at Ft. Collins, Colorado, Davis, California and Yuma, Arizona. A range of water application rates were imposed using the line-source system (Hanks et al., 1976) and in some treatments water was withheld during certain growth stages. Salinity variables were imposed by presalinization before planting and by the use of saline irrigation water. Regardless of irrigation or salinity regime, corn grain and total dry matter production were linearly related to evapotranspiration, which was measured as the sum of irrigation, rainfall and soil water depletion minus drainage. Presalinization of the soil decreased yields in proportion to the salinity imposed, the decrease being associated with reductions in evapotranspiration caused by reduced soil water depletion as compared to the nonsalinized treatments.

Sugar beet production as influenced by limited irrigation

SummarySugar beets (Beta vulgaris L.) were grown on a Millville silt loam soil at Logan, Utah to study the relationships between yield (total dry matter, fresh root, and sucrose) and various levels of irrigation simulating different types of limited irrigation under drought conditions. There were four harvest dates. A model, PLANTGRO, was tested for yield prediction under the imposed conditions. A line source sprinkler irrigation system which applied irrigation water from an excess to a zero amount, was used to impose the various levels of irrigation. Irrigation was continued throughout the season on half of the area and terminated at mid-season on the other half. For both irrigation treatments, yield responses to irrigation levels were large. Unlike continuous irrigation throughout the season, when irrigation was terminated in mid-season, there was no increase in yield (total dry matter, fresh root, or sucrose) from harvest 1 to harvest 4. The relation of yield to termination of irrigation depended on the amount of stored soil water at the time of termination. Yield and relative yield exhibited a strong linear relationship with ET. Percent sucrose was not significantly affected by irrigation regimes or harvest date, but tended to increase as amount of applied irrigation water increased. The model PLANTGRO gave good predictions for relative yields of fresh roots, sucrose, and total dry matter under full-season irrigation. The relative yield relations of fresh roots, sucrose and total dry matter were similar. Where irrigation was terminated in mid-season the model slightly under-predicted yield at high irrigation levels.

Modeling water table contribution to crop evapotranspiration

SummaryA model was developed to account for the time-dependent contribution of the water table to crop evapotranspiration. The same numerical approximation used to solve the water flow in the unsaturated zone was also modified for saturated conditions. For unsaturated flow, the hydraulic conductivity changes with water content and the specific water capacity has finite values. For saturated flow, hydraulic conductivity is constant, and the specific water capacity is zero. The proposed approach considers saturated flow as a special case of unsaturated flow with a constant saturated water content and very small but not zero specific water capacities. Thus flow can be simulated in either unsaturated or saturated zones. The contribution of upward flow to crop evapotranspiration was evaluated during lysimeter experiments in the greenhouse. Spring wheat was planted on asilty clay loam and a fine sandy loam with either no water table or constant water table depths at 50, 100 or 150 cm. Irrigation was applied whenever soil water was depleted below about 50% plant available water. Model predictions of water content and cumulative upward flux as a function of time, for the different water table depths and soils, agreed closely with measured values. The contribution of the water table to evapotranspiration (ET) was found to be 90, 41 and 7% for 50, 100, and 150 cm water table depths respectively for the silty clay loam. Corresponding computed values were 89, 45 and 6%. For the fine sandy loam measured contribution of the water table to ET was 92, 31, and 9% for 50, 100 and 150 cm water tables respectively. Corresponding computed values were 99, 29, and 11 %. It was not practical to simulate the saturated-unsaturated (moving water table) predictions of the model under greenhouse conditions because of the height of the lysimeters needed. Therefore the model was also used to simulate field irrigation management options under several bottom boundary conditions where the water table contributions were significant to crop water use. Results from a one-year simulation were consistent with data for sugarcance grown under similar conditions in the Cauca Valley of Colombia.

Infiltration and runoff as affected by pitting, mulching and sprinkler irrigation

SummaryChanges in infiltration and runoff caused by pitting and mulching under sprinkler irrigation were studied on two soil types. Pitting or diking was done with an implement called a “dammer-diker”. Five soil treatments were applied: shallow and deep “dammer-diker”, shallow “dammer-diker” with mulch, bare, and a mulched soil, combined with two water application rates. Total water infiltration and runoff varied during the experiment. Runoff decreased with area of water storage provided by the pits and the less water was applied. Mulch treatments also reduced runoff. Surface water storage decreased during the season. Changes in soil physical properties due to pitting were more important in controlling runoff than surface water storage.The effective saturated hydraulic conductivity of the soil progressively decreased through the season for all soil treatments and water application rates.A model was developed to simulate the effect of pits on runoff. On a silt loam soil, simulated percent runoff and accumulated runoff over time for the bare and pitted treatments agreed closely to measured values. The agreement of simulated to measured runoff for a silty clay loam soil was not as good probably because of cracking which the simulation model did not take into account.

Corn yield and evapotranspiration under simulated drought conditions

SummaryMeasurements of corn yield and evapotranspiration (ET) were made under a wide variety of limited irrigations simulating drought conditions. Three locations were studied in two seasons. There was a strong linear relation between relative yield and ET (R2 = 0.95 for dry matter yield and R2 = 0.87 for grain yield) where variable irrigation was applied throughout the season as well as where irrigation was applied only at the early part of the season. Yield predictions using the model PLANTGRO (Hanks, 1974) were made from soil, crop, and climatic data. Agreement between prediction and measurements was better for relative dry matter yield (R2 ranged from 0.91 to 0.99) than a relative grain yield (R2 ranged from 0.93 to 0.97). The method for predicting grain yields could be improved but a relation involving seasonal estimates of relative transpiration gave good first-order predictions.

Investigations on power factor of the soil electrical impedance as related to moisture, salinity and bulk density

SummaryThe power factor of the soil electrical impedance was investigated for soils having different textures over a frequency range of 20 kHz–60 MHz. The measurements were carried out in laboratory conditions with different soil water and salinity levels. Within the frequency range of 1–3 MHz the power factor was not significantly affected by soil water contents higher than about 6% (volume) and was also not affected by soil salinity within a range of 0.3–20 dS/m. However, the soil bulk density did influence the magnitude of the power factor. Thus, measurement of soil bulk density, independent of soil water content and salinity, may be possible.

A single point source for the measurement of irrigation production functions

SummaryA study was conducted to determine the possibility of using a single point source sprinkler to provide data for irrigation production functions. Four sprinklers were tested with irrigation initiated by soil water sensors at 15, 35, 60 and 120 kPa of matric suction. Irrigation was automatically applied using a control system. The results show that it was feasible to use a single sprinkler system controlled by soil-water sensors for establishing irrigation production for a given site and time. For the conditions of this experiment, initiating irrigation when the soil dried to 35 kPa at 45 cm depth gave a complete range of irrigation from dry to excessive and produced all of the data needed for a production function. The choice of set-points used to turn irrigation on was quite sensitive. A lower value of matric suction for the set point caused too much irrigation with little additional information. A higher value of matric suction gave good information for low to maximum yield but did not cause excessive irrigation. Further testing may be needed for other site conditions but we believe the general principles of this method will function satisfactorily.

Integrating and applying soil and plant water status measurements

SummaryApplication of soil and plant water status measurements requires some model of the soil-plant-atmosphere system because the measurements made refer to only part of the complex whole. Measurements need to be made to check on the validity of the model and to facilitate adjustment. Since models are only a small imitation of reality they need to be continually checked if application of the results are to be useful. The temptation to use models without checking should be discouraged — modelers should “keep one foot in the field”.

Profits and nitrate leaching under irrigated corn: a simulation

The economic impact of reducing the amount of nitrate leached out of the root zone under irrigation in the arid West was examined. The economic incentives of irrigation management were evaluated under the assumptions of both profit-maximizing and utility-maximizing (in reducing cost and effort expended in irrigation) decision-making criteria. The results indicate that there is a coincidence of interests of the farmer and the environment provided some leaching occurred. If no leaching is allowed, profit decreases markedly. Both behaviors result in less nitrate leaching than less profitable or less utility-producing irrigating practices.