Freddie R. Lamm

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

OPTIMUM LATERAL SPACING FOR SUBSURFACE DRIP-IRRIGATED CORN

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

SUBSURFACE DRIP IRRIGATION USING LIVESTOCK WASTEWATER: DRIPLINE FLOW RATES

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.

Irrigation Scheduling with Planned Soil Water Depletion

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.

NITROGEN FERTILIZATION FOR SUBSURFACE DRIP–IRRIGATED CORN

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.

PARTITIONING OF SPRINKLER IRRIGATION WATER BY A CORN CANOPY

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.

Corn Yield and Water Use Characteristics as Affected by Tillage, Plant Density, and Irrigation

Microirrigation can potentially “spoon feed” nutrients to a crop. Accurately supplying the crop’s nitrogen (N) needs throughout the season can enhance crop yields and reduce the potential for groundwater contamination from nitrates. A 2–year study (1990–1991) was conducted on a Keith silt loam soil (Aridic Argiustoll) to examine combinations of both preplant surface application (30 cm band in center of furrow) and in–season fertigation of N fertilizer for field corn (Zea mays L.) at three different levels of water application (75%, 100%, and 125% of seasonal evapotranspiration) using a subsurface drip irrigation (SDI) system. The method of N application did not significantly affect corn yields, apparent plant nitrogen uptake, or water use efficiency, but all three factors were generally influenced by the combined total N amount. The N application method did have an effect on the amount and distribution of total soil N and nitrate–N in the soil profile following harvest. In both years, nearly all of the residual nitrate–N after corn harvest was within the upper 0.3 m of the soil profile for the treatments receiving only preplant–applied N, regardless of irrigation regime. In contrast, the nitrate–N concentrations increased with increasing rates of N injected by the SDI system and migrated deeper into the soil profile with increased irrigation. The results suggest that N applied with an SDI system at a depth of 40–45 cm redistributes differently in the soil profile than surface–applied preplant N banded in the furrow.

DRIPLINE DEPTH EFFECTS ON CORN PRODUCTION WHEN CROP ESTABLISHMENT IS NONLIMITING

The total sprinkler irrigation amount is partitioned by the crop canopy into three major components: stemflow, throughfall, and interception storage. A study of the partitioning process by a fully developed corn canopy under low wind conditions was conducted. Nearly 3000 measurements of stemflow were made over the course of 23 irrigation/precipitation events using 240 different plants during the two years of the study. At the same time, nearly 300 measurements of the throughfall were made. The objectives were to determine if the process varies between sprinkler types, to determine what factors affect the partitioning process, and to develop models for the process. The partitioning process was examined at three plant spacings and six irrigation amounts under high-pressure impact sprinklers (HI), lowpressure spray heads on drop tubes at a 2.2 m height (LS), low-pressure spray heads at a 4.1 m height (LS-4.1), and also under natural precipitation. Stemflow decreased linearly with plant spacing and increased linearly with irrigation amount. Throughfall increased linearly with both plant spacing and irrigation amount. After tasseling, stemflow is the predominate flow path for sprinkler irrigation water, accounting for 53% at a typical plant spacing of 20 cm. Throughfall accounted for 43% of a typical irrigation amount (25 mm). Interception storage, estimated by algebraic closure, was 1.8 mm when averaged over all events. Comparisons of the developed models with previous research indicates reasonable stability of the partitioning process even though corn production systems and corn plant structure have changed over time. Statistically significant differences occurred in the partitioning process between the LS, LS-4.1 and the HI systems, with the LS-4.1 and HI systems being more similar to natural precipitation. The similarities in stemflow between the LS-4.1 and the HI systems suggests that the differences in stemflow for the LS system may be caused by the height and angle at which applied water intercepts the crop canopy. The average stemflow percentages for the three plant spacings was 46, 43, and 43% for the LS, LS-4.1, and HI systems, respectively.

13. Subsurface drip irrigation

Corn (Zea mays L.) was grown on a deep, well drained silt loam soil (Aridic Argiustolls) at Colby, Kansas, from 2004 to 2007 using three plant densities (66,300, 74,500, or 82,300 plants /ha) under conventional, strip, or no tillage systems for irrigation capacities that were limited to 25 mm every 4, 6, or 8 days. Corn yield increased approximately 10% (1.43 Mg/ha) from the minimum to maximum irrigation capacity in these four years of varying precipitation and crop evapotranspiration. Although strip tillage and no tillage had numerically greater grain yields than conventional tillage in all four years [approx. 8.1% and 6.4% (1.11 and 0.88 Mg/ha), respectively, for the four-year average], strip tillage was significantly greater in only two years and no tillage in only one year. Seasonal water use of the crop tended to be greater for the strip tillage and no tillage treatments as compared to conventional tillage and was significantly greater for strip tillage in two years and for no tillage in one year. The small increases in total seasonal water use (<10 mm) for strip tillage and no tillage correspond with greater grain yields for these tillage systems. Water productivity (grain yield/crop water use) also tended to be numerically greater (three of four years) for the strip tillage and no tillage treatments as compared to conventional tillage because of increased yields for the reduced tillage schemes. Increasing plant density from 66, 300 to 82,300 plants/ha generally increased grain yield and water productivity (four-year average of approximately 6% for each factor). Results suggest that strip tillage obtains the residue benefits of no tillage in reducing evaporation losses without the yield penalty that sometimes occurs with large amounts of residue. Both strip tillage and no tillage should be considered as improved alternatives to conventional tillage, particularly when irrigation capacity is limited.