Don R. Davison

Crop Residue Cover Effects on Evaporation, Soil Water Content, and Yield of Deficit-Irrigated Corn in West-Central Nebraska

Competition for water is becoming more intense in many parts of the U.S., including west-central Nebraska. It is believed that reduced tillage, with more crop residue on the soil surface, conserves water, but the magnitude of water conservation is not clear. A study was initiated on the effect of residue on soil water content and corn yield at North Platte, Nebraska. The experiment was conducted in 2007 and 2008 on plots planted to field corn (Zea mays L.). In 2005 and 2006, soybean was grown on these plots. There were two treatments: residue-covered soil and bare soil. Bare-soil plots were created in April 2007. The residue plots were left untreated. In April 2008, bare-soil plots were recreated on the same plots as in 2007. The experiment consisted of eight plots (two treatments with four replications each). Each plot was 12.2 m × 12.2 m. During the growing season, soil water content was measured several times in each of the plots at six depths, down to a depth of 1.68 m, using a neutron probe. The corn crop was sprinkler-irrigated but purposely water-stressed, so that any water conservation in the residue-covered plots might translate into higher yields. In 2007, mean corn yield was 12.4 Mg ha-1 in the residue-covered plots, which was significantly (p = 0.0036) greater than the 10.8 Mg ha-1 in the bare-soil plots. Other research has shown that it takes 65 to 100 mm of irrigation water to grow this extra 1.6 Mg ha-1, which may be considered water conservation due to the residue. In 2008, the residue-covered soil held approximately 60 mm more water in the top 1.83 m compared to the bare soil toward the end of the growing season. In addition, mean corn yield was 11.7 Mg ha-1 in the residue-covered plots, which was significantly (p = 0.0165) greater than the 10.6 Mg ha-1 in the bare-soil plots. It would take 30 to 65 mm of irrigation water to produce this additional 1.1 Mg ha-1 of grain yield. Thus, the total amount of water conservation due to the residue was 90 to 125 mm in 2008. Water conservation of such a magnitude will help irrigators to reduce pumping cost. With deficit irrigation, water saved by evaporation is used for transpiration and greater yield, which may have even greater economic benefits. In addition, with these kinds of water conservation, more water would be available for competing needs.

FURROW IRRIGATION MANAGEMENT WITH LIMITED WATER

Dwindling water supplies in the Great Plains are a major concern to the economics of the region. Water management studies on limited irrigation usually focus attention on sprinkler irrigation for the delivery system. Furrow irrigation has more management factors that can influence water application including water advance and water distribution over the furrow length. This study compared water application strategies to reduce the amount of water delivered to corn during the vegetative and late grain fill growth periods from 1998 to 2000. In addition to a “full irrigation” and “late initiation of irrigation” treatment, two water allocation treatments were imposed, which limited seasonal water applications to 150 and 250 mm, respectively and “rainfed” treatment. Average grain yield over three years for “late” treatment was 0.2 Mg ha-1 or 2% less than that of “full” treatment. Yields for the 150- and 250-mm treatments were 1.1 and 0.4 Mg ha-1 less than “full.” The reduction in gross water applied was 21%, 36%, and 51% for “late,” 250 mm, and 150 mm as compared to “full”. Soil water was measured to a depth of 1.8 m at quarter points along the furrow to evaluate the distribution of the irrigation. Soil water profiles tended to dry slightly during the season, but there was no statistical difference among the limited and full irrigation treatments. Best management cropping practices were applied, including ridge tillage/planting, furrow packing, irrigation scheduling, and surge irrigation techniques to keep water in the soil profile and target water applications to critical crop growth stages.. These practices maximized the potential success of all irrigation treatments.

Effects of Crop Residue Removal on Soil Water Content and Yield of Deficit-Irrigated Soybean

Reduced tillage, with more crop residue remaining on the soil surface, is believed to conserve water, especially in arid and semi-arid climates. However, the magnitude of water conservation is not clear. An experiment was conducted to study the effect of crop residue removal on soil water content, soil quality, and crop yield at North Platte, Nebraska. The same field plots were planted to soybean (Glycine max) in 2009 and 2010. There were two treatments: residue-covered soil and bare soil. Residue (mostly corn residue in 2009 and mostly soybean residue in 2010) was removed every spring from the same plots using a flail chopper and subsequent hand-raking. The experiment consisted of eight, 12.2 m × 12.2 m, plots (two treatments with four replications each). Soybeans were sprinkler-irrigated, but purposely water-stressed, so that any water conservation in the residue-covered plots might translate into higher yields. After four years of residue removal, soil organic matter content and soil residual nitrate nitrogen were significantly smaller, and soil pH was significantly greater, in the bare-soil plots compared to the residue-covered plots. The residue-covered soil held approximately 90 mm more water in the top 1.83 m compared to the bare soil near the end of the 2009 growing season. In addition, mean soybean yield was 4.5 Mg ha-1 in the residue-covered plots, compared to 3.9 Mg ha-1 in the bare-soil plots. Using two crop production functions, it is estimated that between 74 and 91 mm of irrigation water would have been required to produce this extra 0.6 Mg ha-1. In 2010, mean soybean yield was 3.8 Mg ha-1 in the residue-covered plots, compared to 3.3 Mg ha-1 in the bare-soil plots. Between 64 and 79 mm of irrigation water would have been required to produce this extra 0.5 Mg ha-1. In both years, several processes may have contributed to the differences observed: (1) greater evaporation of water from the soil in the bare-soil treatment, and (2) greater transpiration by plants in the bare-soil treatment in the beginning of the growing season as a result of more vegetative growth due to higher soil temperatures in the bare-soil treatment.

Effect of Amount and Timing of Subsurface Drip Irrigation on Corn Production

Subsurface drip irrigation (SDI) has the potential of being a more efficient irrigation system compared to systems such as center pivot and furrow irrigation. The objective of this study was to determine the effect of the amount and timing of irrigation, using SDI, on corn (Zea mays) production. A field study was conducted at North Platte, Nebraska in 2007 and 2008, using two SDI systems. The study was replicated eight times on the older SDI system (SDI1) and four times on the newer SDI system (SDI2). On SDI1, there were nine treatments to impose different irrigation regimes, ranging from dryland to fully irrigated. Five of the nine treatments allowed water stress only after tasseling and silking. On SDI2, there were eight treatments that were very similar to the nine on SDI1.

Corn Water Use and Yield for Various Limited Irrigation Treatments

With limited water resources, it becomes more critical to know how much and when to irrigate. The objective of this study was to determine the effect of the amount and timing of irrigation on corn (Zea mays L.) yield using subsurface drip irrigation (SDI). A field study was conducted at North Platte, Nebraska in 2007 - 2009, using two SDI systems. The study was replicated eight times on the older SDI system (SDI1) and four times on the newer SDI system (SDI2). On SDI1, there were nine treatments to impose different irrigation regimes, ranging from dryland to fully irrigated. Five of the nine treatments allowed for various degrees of water stress, but only after tasseling and silking. On SDI2, there were eight treatments that were very similar to those on SDI1.

Effect of Crop Residue on Soil Water Content and Yield of Deficit-Irrigated Corn and Soybean

It is believed that reduced tillage, with more crop residue on the soil surface, conserves water, especially in arid and semi-arid climates. However, the magnitude of water conservation is not clear. In 2007, a study was initiated on the effect of residue on soil water content and crop yield at North Platte, Nebraska. The experiment was conducted on plots planted to field corn (Zea mays L.) in 2007 and 2008, and soybean (Glycine max) in 2009. There were two treatments: residue-covered soil and bare soil. Bare-soil plots were created in April 2007 by using a dethatcher and subsequent hand-raking. In April 2008 and 2009, bare-soil plots were recreated on the same plots as in 2007. The experiment consisted of eight plots (two treatments with four replications each). Each plot was 12.2 m by 12.2 m. The crop was sprinkler-irrigated, but purposely water-stressed, so that any water conservation in the residue-covered plots might translate into higher yields.