Abstract

The dry bean (Phaseolus vulgaris L.) crop is sensitive to irrigation management. Irrigation efficiency, water quality, and yield production are concerns in southwestern Colorado. This field study was conducted in 1992 and 1994 at the Southwestern Colorado Research Center to study the effects of five irrigation rates on dry bean seed yield and dry matter. The soil on the site is Wetherill silty clay loam (fine-silty, mixed, superactive, mesic, aridic haplustalf). A surface drip irrigation system was used to achieve the irrigation rates of 0.00, 0.33, 0.67, 1.00, and 1.33 of the estimated evapotranspiration (ET). The experiment was set up using a randomized complete block design with four replications. Optimum conditions during the 1992 season led to higher dry matter and seed yields than in 1994. Irrigation rates had a significant effect on total aboveground dry matter (TDM) and seed yield in both years. There was no significant increase in seed yield and TDM beyond 0.67ET and 1.00ET, respectively, in 1992. However, maximum seed yield was obtained at a 0.67ET irrigation rate in the cooler year (1992), while 1.00ET or greater was required to achieve maximum biomass yield in both years. Total DM and seed yield continued to increase up to 1.33ET in 1994, reaching a similar level as in 1992. Irrigation use efficiency declined as the irrigation rate increased in both years. The pattern of biomass accumulation was similar in 1992 and 1994, as more growth occurred with the greater irrigation rates. Visual observations revealed a shallower root system under the higher irrigation rates than under the nonirrigated (0.00ET) and the limited-irrigation (0.33ET) treatments. This was confirmed by the soil moisture profile at harvest in 1992 and 1994. Dry bean can extract soil water from the 0 to 24 in. soil profile under dryland conditions, and from the 0 to 12 in. soil profile under well-irrigated conditions (1.00ET). Soil moisture content below 12 in. was at or near field capacity under the over-irrigation treatment (1.33ET), which suggests the potential for deep percolation and leaching of nitrates and other soluble salts. Over-irrigation appears to encourage a shallow root system, less than 2 ft. (field plant root inspection), which may reduce the use of soil moisture at lower depths and encourage deep percolation to the groundwater.

Research Question

Concerns about irrigation efficiency, water quality, and yield have prompted this study. Over-irrigation is a key factor that contributes to deep percolation and nutrient leaching to the groundwater. The objective of this study was to determine the effect of five different irrigation rates on dry bean yield response and water use efficiency.

Literature Summary

The dry bean is very sensitive to irrigation management. Studies indicate that dry bean yields can vary significantly as irrigation rates go from dryland to optimal rates. However, the increase in yield may not be significant with the increase of the irrigation rate beyond optimum water need. It was reported that dry bean can extract water from the soil profile much deeper under dry and limited-irrigation conditions than over-irrigated conditions.

Study Description

The field study was conducted to investigate the impact of five irrigation rates on dry bean growth response. The irrigation rates used in this study were 0.00, 0.33, 0.67, 1.00, and 1.33 of estimated evapotranspiration (ET). The soil on the site is Wetherill silty clay loam. The experiment was a randomized block design with four replications. A surface drip irrigation system was used to achieve the complete designed irrigation rates. An irrigation scheduling program was used to manage irrigation. Weather data from a local weather station on the site was used to estimate ET by using the Penman Equation. The water balance approach was used to determine the 1.00ET irrigation rate based on estimated ET, precipitation (total seasonal precipitation was 7.6 and 5.0 in. from June to September of 1992 and 1994, respectively), change in soil moisture, runoff, and drainage terms in the 1992 and 1994 seasons.

Applied Questions

How does dry bean respond to different irrigation rates?

Seed yield and dry matter increased significantly as the irrigation rates were increased up to the optimal water use (1.00ET) in 1994. However, maximum seed yield was obtained at 0.67ET in the cooler year (1992), while 1.00ET or greater was required to achieve maximum biomass yield in both years. Improvement in the yield was related to the water and irrigation use efficiencies, where yield production (seed or dry matter) per 1 in. of applied or used water was greater when the irrigation rate was kept at or below 1.00ET. Therefore, exceeding plant water requirements not only leads to waste of water, but also can affect plant performance and soil environment. What is the impact of the irrigation rate on soil water use or root moisture extraction pattern?

Over-irrigation encouraged a shallow root system. The effective root depth under an irrigation rate greater than 1.00ET was 12 in. Conversely, limited irrigation treatments encouraged the development of a deeper root system and water uptake down to 3-ft. Also, the soil moisture profile under over-irrigated and 1.00ET was close to field capacity during the growing season, which may lead to potential deep percolation and nutrient loss to the groundwater.

Recommendation

Dry bean production in semi-arid climate areas like southwestern Colorado can be improved significantly by using proper irrigation scheduling. Irrigation scheduling can improve irrigation and water use efficiencies, especially in areas such as southwestern Colorado, where water management is critical to crop yield and water quality. The dry bean root system can use soil moisture more efficiently from lower depths (24 in. or deeper) when optimum irrigation was applied (equal to or less than 1.00ET). However, the irrigation scheduling program (SCHED) may have overestimated water requirements in the cooler year to achieve maximum seed yield, while predicting the water requirements needed for maximum biomass yield at 1.00ET or greater in both years.

Copyright © 1999. . Copyright © 1999 by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, 5585 Guilford Rd., Madison, WI 53711 USA