Danny H. Rogers

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.

AN ECONOMIC COMPARISON OF SUBSURFACE DRIP AND CENTER PIVOT SPRINKLER IRRIGATION SYSTEMS

In the U.S. Great Plains region many irrigation systems have been converted from traditional furrow to more efficient center pivot sprinkler irrigation. Irrigators are also expressing interest in use of subsurface drip irrigation (SDI) but are concerned about the economics of its use on major field crops, such as corn. A study was conducted to analyze SDI profitability relative to center pivot sprinkler cropping systems, focusing on continuous irrigated corn production in western Kansas. Results indicated that for 65 ha fields, SDI had a distinct disadvantage in net returns of

SUBSURFACE DRIP IRRIGATION USING LIVESTOCK WASTEWATER: DRIPLINE FLOW RATES

54/ha. As field size declined, per ha investment costs for center pivots increased markedly, whereas SDI system costs adjusted proportionally. As a result SDI net returns were approximately equal to center pivot sprinkler systems for 25.9 ha fields, and greater for 13 ha fields (a

Irrigation Scheduling with Planned Soil Water Depletion

28/ha SDI advantage). These results are very sensitive to SDI life. SDI was unprofitable relative to center pivot sprinklers for SDI life of less than 10 years. Changes in corn yield and price, and dripline costs also affected the relative profitability of SDI.

CORN YIELDS AND PROFITABILITY FOR LOW–CAPACITY IRRIGATION SYSTEMS

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.

MEASURED AND SIMULATED UNIFORMITY OF LOW DRIFT NOZZLE SPRINKLERS

A two-year study was initiated in the spring of 1990 on a Keith silt loam soil (Aridic Argiustoll) in northwest Kansas to determine if irrigation scheduling with planned soil water depletion could be used successfully for irrigated corn (Zea mays L.) as a method of conserving and protecting groundwater resources without reducing yields. The study was conducted using surface irrigation in small dead-level basins. Planned soil water depletion was attempted by allowing a small additional daily deficit (0, 1, or 2 mm/day) to accumulate in irrigation amounts as scheduled by an evapotranspiration (ET)-based water budget. The daily deficit amounts were imposed on three irrigation levels, heavy (1.25 ¥ ET), normal (1.00 ¥ ET), and deficit (0.75 ¥ ET) which represented a range of management by irrigators. The plant-available soil water at physiological maturity was related linearly to irrigation amounts. However, the plant-available soil water at physiological maturity was reduced by only 25 mm for each 100 mm reduction in irrigation. Imposition of a small daily deficit of 1 mm/day after tasseling resulted in yield reductions of 7, 1, and 3% for the heavy, normal, and deficit irrigation management levels, respectively. The 1 mm/day deficit resulted in irrigation savings of approximately 12, 9, and 0% for the three respective irrigation management levels and generally resulted in slight reductions in available soil water at physiological maturity. In some cases, the imposition of the 1 mm/day deficit had little effect on the total seasonal irrigation amount, but simply shifted the irrigation event to a later date. The larger 2 mm/day daily deficit after tasseling reduced yields by 7, 9, and 15% for the three respective irrigation levels and reduced irrigation amounts by 19, 26, and 25%. Yields were related linearly to irrigation and water use with a reduction in irrigation or water use reflected by yield reductions. Water use efficiencies were similar whether planned soil water depletion was used or not. Therefore, from a water conservation standpoint, irrigation scheduling with planned soil water depletion was not justified.

SENSITIVITY OF THIN-WALLED DRIP TAPE EMITTER DISCHARGE TO WATER TEMPERATURE

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

ON-FARM SCHEDULING STUDIES AND CERESMAIZE SIMULATION OF IRRIGATED CORN

1000 to

SOIL WATER SURVEY AFTER CORN HARVEST IN NORTHWEST KANSAS

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.

Twenty Years of Progress with SDI in Kansas.

Field measurements conducted on large–scale irrigation systems with fixed–plate, low drift nozzle (LDN) sprinklers showed that coefficient of uniformity (CU) values ranged from 70 to over 90. Measured CU values were typically lower in value for the lower operating pressure systems and for sprinkler packages with wider spacings. Measured single–sprinkler distribution patterns were then used in an overlapping sequence with specific sprinkler spacing scenarios to simulate multiple–sprinkler distribution patterns for moving systems. Scenarios included sprinkler operating pressures of 41, 69, 104, and 138 kPa; sprinkler spacings of 1.83, 2.44, 3.05, and 3.66 m; and nozzle orifice sizes of 4.76 to 7.94 mm with a flow range of 0.16 to 0.77 L/s. Simulated patterns and CU values compared well with field–measured patterns and CU values for the respective sprinkler size, spacing, and operating pressure combinations. CU values from simulated patterns were highest for closer sprinkler spacing scenarios (<2.4 m) and higher operating pressures (104 and 138 kPa; still in the low range for sprinkler systems). However, evaporative and wind losses could be higher than with the lower operating pressures, thus reducing the overall application efficiency. Based on the spacing, nozzle size, and operating pressure scenarios tested in this research, sprinkler spacing to wetted diameter ratios should not exceed 0.20 in order to achieve coefficients of uniformity in excess of 90 under no–wind conditions with fixed–plate, LDN–type sprinklers.