Improving Furrow Irrigation Efficiency for Midsouth Soybeans
There are two certainties regarding irrigation of Midsouth crops.
• According to a 2018 NASS survey, over 80% of the irrigated acres in Arkansas, Louisiana, Mississippi, and Tennessee have water applied by gravity flow delivery systems. By far the most-used method in gravity flow systems is furrow irrigation through lay-flat polyethylene tubing.
• The preponderance of results from research indicate that furrow irrigation is not very efficient–typically about 65%. This means that a considerable amount of irrigation water that is applied with this system is not used by the crop it is applied to. This is a concern from both efficiency–i.e. wasted water–and economic points of view.
The above two points should provide impetus for producers to adopt scheduling and irrigation application practices that will increase furrow irrigation efficiency. A summary of these practices can be found here and here.
A publication titled “Furrow Irrigation Application Efficiency in Midsouthern USA Conservation Tillage Systems” (https://doi:10.1002/agj2.20468) by Bryant et al. appears in a recent issue of Agronomy Journal. The contents of this article report the results from research that was conducted at Stoneville, Miss. to determine if the efficiency of furrow irrigation could be altered/enhanced by type of tillage system used to grow soybeans. The following points summarize the conduct of and results from this research.
• Research with soybeans was conducted during the 2015-2018 growing seasons.
• The objective of the research was to determine if furrow advance time, infiltration, and runoff volumes, and irrigation application efficiency (IAE) and irrigation water use efficiency (IWUE) can be manipulated by adopting conservation production practices in soybean production systems.
• The soil series at the study site was a Bosket very fine sandy loam transitioning to a Dubbs silt loam. Both soils have low organic matter and experience surface crusting after wetting.
• There were seven treatments as follows.
Conventional tillage/winter fallow (CT/WF): fall disking; soybeans planted on beds formed in the spring; natural winter vegetation chemically desiccated prior to soybean planting; most tillage intensive treatment.
Reduced tillage/winter fallow (RT/WF): soybeans planted on beds formed in the fall; natural winter vegetation chemically desiccated prior to soybean planting.
Reduced tillage/subsoiling (RT/SS): same as RT/WF except subsoiled prior to fall bed formation.
Reduced tillage/cereal rye cover crop (RT/RC): same as RT/WF except cereal rye was seeded as a cover crop in the fall in lieu of subsoiling, and was chemically desiccated and rolled in early May prior to soybean planting.
Reduced tillage/tillage radish cover crop (RT/TR): same as RT/RC except tillage radish was sown as a cover crop instead of cereal rye, and desiccated at bolting.
Zone tillage/winter fallow (ZT/WF): no fall or spring tillage except the planting operation; natural winter vegetation chemically desiccated prior to soybean planting on unbedded ground.
Zone tillage/tillage radish cover crop (ZT/TR): same as ZT/WF except tillage radish was sown and managed as in RT/TR.
• A MG IV soybean variety was planted in early May each year.
• Irrigation was scheduled according to FAO-56, and was delivered via lay-flat polyethylene tubing. All treatments were irrigated simultaneously. PHAUCET was used to determine hole size along the tubing run.
• Water application volume and furrow flow rates were measured at the field inlet and for each treatment.
• In-season data were collected to determine percentage ground cover, cover crop biomass, furrow advance time, runoff volume, IAE, and IWUE.
• Across years, ground cover in RT/WF and RT/SS was 42% and 44%, respectively, while ground cover in CT/WF was <5%. Thus, conservation tillage ground cover requirements were met in the RT treatments.
• Furrow advance time took the longest in RT/SS, and furrow runoff was greatest and furrow infiltration amount and IAE were the least in RT/WF.
• Across years, IWUE was similar for CT/WF, RT/WF, and RT/SS, and ranged from from an average of 21.5 to 23.75 kg/mm of added water.
• Furrow advance time took the longest in RT/RC compared to that in RT/SS and RT/TR, while furrow infiltration rate and runoff were similar across the three treatments. There was little to no difference in IAE and IWUE among these three treatments.
• There was no significant difference in furrow advance time, infiltration rate, and runoff among RT/SS, ZT/WF, and ZT/TR, nor was there any difference in IAE and IWUE among these three treatments.
• Relative to conventional tillage, IAE was maintained in reduced tillage systems when subsoiling was included. Thus, subsoiling apparently improved IWUE in the reduced tillage systems.
• These results indicate that midsouthern soybean producers can maintain or improve IAE and IWUE by transitioning to a conservation tillage system if subsoiling is included on soils with these textures.
• Replacing subsoiling with a cover crop had no effect on IAE.
• Replacing subsoiling with a cereal rye cover crop maintained IWUE in the RT treatment, but net returns were reduced. Thus, replacing subsoiling with a cereal rye cover crop is not economically feasible on these soils.
• Zone tillage systems with or without a cover crop maintained IWUE relative to that of RT/SS, but the increased risk of replanting these flat-planted systems is greater.
• Overall, these results indicate that Midsouth soybean producers can maximize furrow irrigation functionality, yield, and profitability while minimizing risk by transitioning from a conventional tillage system to a conservation tillage system on medium- to coarse-textured soils if subsoiling but not cover crops is included.
An Irrigation White Paper on this website provides details and links to articles that contain information about the various water conservation measures that should be used when applying water by the furrow method regardless of the production system that is used.
Click here for an article on this website that describes other technologies that can be used for Midsouth crop irrigation. The sustainability of Midsouth irrigation will likely depend on the refinement and use of all water saving technologies that are now or will become available.
Composed by Larry G. Heatherly, Nov. 2020, larryheatherly@bellsouth.net