Loyd R. Stone

Water requirement of subsurface drip-irrigated corn in Northwest Kansas

Irrigation development during the last 50 years has led to overdraft in many areas of the large Ogallala aquifer in the central United States. Faced with the decline in irrigated acres, irrigators and water resource personnel are examining many new techniques to conserve this valuable resource. A three-year study (1989 to 1991) was conducted on a Keith silt loam soil (Aridic Argiustoll) in northwest Kansas to determine the water requirement of corn (Zea mays L.) grown using a subsurface drip irrigation (SDI) system. A dryland control and five irrigation treatments, designed to meet from 25 to 125% of calculated evapotranspiration (ET) needs of the crop were examined. Although cumulative evapotranspiration and precipitation were near normal for the three growing seasons, irrigation requirements were higher than normal due to the timing of precipitation and high evapotranspiration periods. Analysis of the seasonal progression of soil water revealed the well-watered treatments (75 to 125% of ET treatments) maintained stable soil water levels above approximately 55 to 60% of field capacity for the 2.4-m soil profile, while the deficit-irrigated treatments (no irrigation to 50% of ET treatments) mined the soil water. Corn yields were highly linearly related to calculated crop water use, producing 0.048 Mg/ha of grain for each millimeter of water used above a threshold of 328 mm. Analysis of the calculated water balance components indicated that careful management of SDI systems can reduce net irrigation needs by nearly 25%, while still maintaining top yields of 12.5 Mg/ha. Most of these water savings can be attributable to minimizing nonbeneficial water balance components such as soil evaporation and long-term drainage. The SDI system is one technology that can make significant improvements in water use efficiency by better managing the water balance components.

Response of corn, grain sorghum, and sunflower to irrigation in the High Plains of Kansas☆

Abstract Groundwater is being mined in much of the irrigated area of the central and southern High Plains of the USA. Profits and risks inherent in irrigation management depend on the association between crop yield and level of water application. Research was conducted over a 14 year period (1974–1987) to establish the yield vs. water application relationships of corn, grain sorghum, and sunflower. The research was located near Tribune, Kansas, USA on a Ulysses silt loam soil. Plots were level-basins to which water was added individually through gated pipe. Irrigation studies of the three crops were located adjacent to each other. Irrigation treatments were arranged in completely randomized blocks with three replications. As total irrigation amount increased from 100 to 200, 200 to 300, and 300 to 400 mm, sunflower yield increased by 0.53 Mg ha−1, 0.43 Mg ha−1, and 0.37 Mg ha−1, respectively. Corn outyielded grain sorghum at total irrigation amounts of 345 mm and above. Yield increase over continuous dryland was greater in corn than in grain sorghum at total irrigation amounts above 206 mm. Therefore, if grain mass is the consideration, grain sorghum is a better choice than corn at less than 206 mm of irrigation, whereas corn is a better choice than grain sorghum at more than 206 mm of irrigation.

OPTIMUM LATERAL SPACING FOR SUBSURFACE DRIP-IRRIGATED CORN

A two-year study was initiated in the spring of 1990 on a Keith silt loam soil (Aridic Argiustoll) in northwest Kansas to determine the optimum dripline lateral spacing for irrigated corn (Zea mays L.) using subsurface driplines installed at a depth of 40-45 cm in a direction parallel to the corn rows. Average corn yields were 13.6, 12.8, and 12.2 Mg/ha for dripline spacings of 1.5, 2.3, and 3.0 m, respectively, for a seasonal-irrigation amount of 462 mm. Yields decreased to 10.8 and 9.3 Mg/ha when irrigation was reduced by 33 and 50% for the wider 2.3- and 3.0-m dripline spacings, respectively. The wider dripline spacings resulted in nonuniform horizontal distribution of available soil water. As a result, yields decreased with horizontal distance from the dripline. The highest yield, highest water use efficiency, and lowest year-to-year variation were obtained with the 1.5 m dripline spacing. An economic analysis indicated that because yield reductions were so great, the wider dripline spacings would be justified only at very high dripline costs and or very low corn grain prices.

SUBSURFACE DRIP IRRIGATION USING LIVESTOCK WASTEWATER: DRIPLINE FLOW RATES

Using subsurface drip irrigation (SDI) with lagoon wastewater has many potential advantages. The challenge is to design and manage the SDI system to prevent emitter clogging. The objective of this study was to measure the flow rates of five types of driplines (with emitter flow rates of 0.57, 0.91, 1.5, 2.3, and 3.5 L/h/emitter) when used with lagoon wastewater. A disk filter with openings of 55 µm (200 mesh) was used and shock treatments of chlorine and acid were injected periodically. During the 1998 growing season, 530 mm of wastewater were applied through the SDI system and 390 mm were applied in 1999. During the growing seasons, the two lowest flow rate emitter designs decreased in flow rate, indicating that some emitter clogging had occurred. The magnitudes of the decreases were 15% and 11% of the original flow rates in 1998 and 22% and 14% in 1999 for the 0.57 L/h/emitter and 0.91 L/h/emitter driplines, respectively. After the winter idle period, the flow rates of both driplines returned to the initial flow rates. The three emitter designs with higher flow rates showed little sign of clogging; their flow rates decreased by 4% or less through both growing seasons. Observations showed that the disk filter and automatic backflush controller performed adequately in 1998 and 1999. Based on these preliminary results, the use of SDI with lagoon wastewater shows promise. However, the smaller emitter sizes (0.91 L/h/emitter or less) may be risky for use with wastewater and the long-term (greater than two growing seasons) effects are untested.

Soil water depletion by sunflower and sorghum under rainfed conditions

Abstract Grain sorghum [ Sorghum bicolor (L.) Moench] and sunflower ( Helianthus annuus L.), were grown under rainfed conditions in 1988 and 1989 near Manhattan, Kansas, on a Muir silt loam (Cumulic Haplustoll, fine-silty, mixed, mesic) to determine if the two crops exploited water at different depths and at different rates in the soil. Soil water content was measured weekly to a depth of 3.20 m with a neutron probe to ascertain depletion rate and depth. Transpiration, stomatal resistance, canopy temperature, and plant water potential also were analyzed to help explain any differences in soil water depletion that might be observed. Sunflower depleted water to a deeper depth, and had a higher rate of depletion at lower depths, than sorghum. In 1988 and 1989, sunflower depleted water to 2.55 and 2.70 m, respectively. About 90% of the total water used by sorghum was from the 0 to 1.65 m and 0 to 1.50 m depth in 1988 and 1989, respectively. Sunflower had a higher rate of depletion compared to sorghum below the 1.20 m depth (1988) and the 1.65 m depth (1989). Sunflower had a higher transpiration rate, lower stomatal resistance, cooler canopy temperature, and higher leaf water potential compared to sorghum, perhaps because, in part, sunflower could exploit more water at deeper soil depths. The results suggested that sunflower might be planted in rotations with shallow-rooted crops or after irrigated crops to take advantage of water at depth.

Crop Production and Economics in Northwest Kansas as Related to Irrigation Capacity

Crop production and economics of corn, grain sorghum, soybean, and sunflower under irrigated and dryland conditions were simulated using 34 years (1972-2005) of weather data in Northwest Kansas. Irrigation system capacities ranged from 2.5 to 8.5 mm/day. The simulated long-term annual average net irrigation requirements for corn, grain sorghum, soybean, and sunflower were 375, 272, 367, and 311 mm, respectively. Assuming a 95% application efficiency (Ea), the average long-term crop yield is approximately 12.9, 8.2, 4.4, and 3.2 Mg/ha for corn, grain sorghum, soybean, and sunflower, respectively. Although corn is currently the predominant irrigated crop in western Kansas, projections for the year 2006 indicate soybean is a more profitable alternative. Net irrigation requirements for soybean are only about 2% lower than corn, so a shift to soybean will not result in significant water conservation. If the price of corn increased just 10% relative to stable prices for the other crops, it would become the most profitable irrigated crop. This indicates that net return projections are very volatile, subject to changes in crop prices and input costs.

CORN YIELDS AND PROFITABILITY FOR LOW–CAPACITY IRRIGATION SYSTEMS

In many areas of the central U.S. Great Plains irrigation well capacities are decreasing due to declines in the Ogallala aquifer. Many producers using furrow surface irrigation are faced with a decision on whether they should convert to a higher efficiency center pivot sprinkler irrigation system. An irrigation scheduling model using 27 years of climatic data for western Kansas was combined with a corn yield production function and economic model to simulate crop yields and economics under four combinations of irrigation system and application efficiency for six different irrigation capacities. Center pivot sprinkler irrigation systems were found to give higher corn yields and greater profitability than furrow surface irrigation, particularly when system flow rates were less than 40 L/s. Sprinkler irrigation systems with application efficiencies of 100, 95, and 85% and a furrow surface irrigation system with 70% application efficiency produced simulated crop yields of 12.3, 12.2, 12.1, and 11.3 Mg/ha, respectively, when irrigation capacity was 6.35 mm/day. Reducing the irrigation capacity to 2.54 mm/day reduced yields to 9.4, 9.2, 8.9, and 8.3 Mg/ha for the respective irrigation systems. Net annual returns for a 65 ha field were increased by US

Canopy temperature and growth of differentially irrigated alfalfa

1000 to

Water Allocation Model for Limited Irrigation

4000 with center pivot sprinkler irrigation compared to furrow surface irrigation for system flow rates between approximately 20 and 40 L/s. Labor savings with sprinkler irrigation are a significant factor in profitability, but increased crop yields are also very important, particularly at lower system flow rates of approximately 20–30 L/s.

Equations for Drainage Component of the Field Water Balance

Abstract Plant temperature of alfalfa (Medicago sativa L.) grown with different amounts of irrigation water has not been reported. The objective of this experiment was to determine if progressive differences in canopy temperature existed among plots of alfalfa (ev. Cody) subjected to 7 graded watering treatments. Irrigation water (0, 2.5, 5.1, 7.6, 10.2, 12.7, 15.2 cm) was added after each of three harvests in 1980 and 1981. Extremes in weather between the summers of 1980 and 1981 enabled comparison of data from a stressed season (1980) with those from a non-stressed season (1981). Throughout the growth period in both years, canopy temperatures, leaf area, stem dry weight, leaf dry weight and total dry weight were determined. Canopy temperature was measured with an infrared thermometer. The relationship between canopy-minus-air temperature (Tc — Ta) versus vapor-pressure deficit (VPD) was determined on well watered alfalfa for 1980 and 1981. Differences in canopy temperature, leaf area index, leaf dry weight, stem dry weight, and total dry weight, due to treatments, were evident in the dry year (1980), but not in the wet year (1981). In the dry year, the irrigated plots generally had cooler canopy temperatures and higher dry weights than the dry land plots, but differences due to the level of water added were not apparent. In both the dry year and the wet year, (Tc — Ta) was inversely related to VPD. Also, in both years, and for all treatments, leaf dry weight was about equal to stem dry weight.