Dry Bean Production Under Limited Irrigation
Flowering and pod fill are critical growth stages for water stress.
Production
practices that maximize economic return for the dry bean crop recommend
irrigation when the available soil moisture reaches approximately 50%.
In our region, this equates to approximately 16 to 20 inches of water
during the growing season. During peak water use periods, dry beans require
approximately 0.30 inches of water per day, similar to corn, sugar beets
and alfalfa. However, because dry beans are a short season crop they result
in a shorter water demand period (Yonts, 1996). The question many bean
producers are asking is how to reduce season water requirements. Further,
can the bean crop withstand lower soil moisture conditions during a portion
of the growing season, and what cultural practices can be implemented
to reduce the effects of limited soil moisture. From a management perspective,
the question becomes, can irrigation be limited without jeopardizing yield
potential and net return? The answer to this question is related to many
factors in the production system including, crop rooting depth, timing
of soil moisture stress, soil texture, density and depth, quality of the
irrigation water, the variety of bean, severity of root diseases, and
rate of evapotranspiration during the growing season.
The rooting depth of a crop greatly influences the ability to extract soil moisture. The maximum rooting depth for dry beans is 24 to 30 inches (Yonts, 1996). On most soils, bean roots in the upper 18 inches of the soil profile extracted 85% of the total crop needs. Therefore, beans have a shallow rooting system compared to other crops such as corn, wheat, sunflower or small grains and require more frequent watering, especially during the reproductive stage of growth (pod set and fill) when the air temperature is high.
The reproductive stage is the most critical time during the life cycle of the bean crop to limit or prevent soil moisture deficits. Research at Colorado State University studied the effects irrigation level and timing have on pinto bean production (Bandaranayake, 1990). In that study, the crop was watered at 30, 50 and 70 % available soil moisture during the vegetative and reproductive stages of growth to simulate high, medium and low soil moisture stress levels, respectively. A non-irrigated check treatment was included that had a yield of 1726 lbs/acre. This yield was higher than expected because timely and excessive rain occurred during the growing season. Mean yield for treatments that had high and low stress during the reproductive stage of growth with no stress during the vegetative stage was 2443 and 3335 lbs/acre, respectively. Mean yield for treatments that had high and low stress levels during the vegetative stage of growth with no stress during the reproductive period were not statistically different (3535 vs 3220 lbs/acre). These results clearly demonstrated that stress during the reproductive stage was more critical than during the vegetative stage. Caution should be taken when making conclusions from this data because the research was only conducted in one site-year. However, the trend was very clear, limited available soil moisture during the vegetative stage had little effect on seed yield, but during reproductive growth it reduced seed yield by almost 900 lbs/acre.
A method to estimate yield losses due to limited soil moisture, termed the FAO method, was reported by Allen, Yonts and Wright (2000). That method estimates yield based on limiting evapotranspiration due to soil moisture stress during the growing season. They reported that when seasonal ET was limited by 30 % during the vegetative period, yield was predicted to decline 6 %. However the same reduction in ET during flowering would reduce yield 33 %. The authors reaffirmed that flowering and pod fill periods were the most sensitive periods for the bean crop.
Irrigation water should be limited during late season. Irrigation should be terminated when 20% of the lower leaves and pods have turned yellow due to physiological maturity (Yonts, 1996). Irrigating late in the season can delay maturity and increase disease potential by saturating the root zone when the plant only requires minimal water.
Monitor soil moisture every week during June, then twice a week or more during July and early August. Always try to apply sufficient water to refill the root zone plus a small margin to account for root growth that will occur before the next irrigation. Irrigation water applied beyond the root zone is wasted. During the reproductive stage, try to irrigate when the air temperature is less than 70 to 800 to prevent temperature shock to the plant that can cause floral abortion.
Soil structure and tilth play important roles to determine the depth of root penetration, efficiency of soil moisture extraction, and amount of water the soil can hold. The presence of layers that restrict root growth, such as hard pans, will reduce the rooting depth, consequently the ability of the plant to extract soil moisture. Soil compaction can significantly reduce bean yields by limiting root growth, preventing water from infiltrating through the soil profile, and increasing the incidence of root rot disease. If a compacted layer occurs, the field should be deep chiseled and/or planted to a crop that is less sensitive to compaction, such as corn, sunflower or wheat. Deep chiseling should only be done when the soil is relatively dry, because the chisel points do not break up or fracture the compacted layer in wet soil.
Poor soils, such as those that have salinity problems or
low organic matter, do not hold soil moisture or respond to fertilization.
Because beans are extremely sensitive to soil salinity (Blaylock, 1996),
production of beans on fields that have a history of salinity problems
should be avoided, especially if irrigation water is reduced. Since most
crops are more tolerant than beans, fields that have a history of salt
problems should be planted to an alternative crop such as barley, sugarbeets
or sorghum.
Varieties differ in their response to drought stress. Research at Colorado
State University has shown that varieties in the pink market class, such
as Rosa and Viva, are among the most tolerant of drought stress. In general,
varieties in the pinto market class that have a vigorous vine growth habit
and full season maturity are more tolerant to drought stress than upright
short season varieties. The ability to withstand low soil moisture is
related to a variety’s ability to produce vegetative growth to shade
the soil surface and have an extended period of pod set and fill to maximize
the opportunity to produce seed. Alternatively, varieties with early season
maturity can reduce total seasonal water needs, and a variety such as
Othello may be a good choice if irrigation water will be available during
the critical flower and pod fill stages.
Dryland varieties, developed by the breeding program at Colorado State University for the nonirrigated regions of the San Juan Basin in SW Colorado and NW New Mexico, are not adapted to the High Plains. The most recent releases, Fisher and Cahone, were developed for dryland systems in this region, however, they are not recommended for the High Plains because neither has resistance to pathogens in the High Plains, such as rust and common bacterial blight, and they are very long season (>105 days) when grown outside of their region of adaptation.
Management with limited irrigation is more critical than with full irrigation. Scout bean fields twice weekly. Carefully observe both upper and lower leaf surfaces for disease or insect pests, dig plants to inspect rooting patterns, soil moisture, nodulation and the general health of the root system. Be especially aware of patterns in the field that could indicate early disease infection, poor water distribution, or other problems that can be addressed in a management program, including the timely application of pesticides. Production systems under limited irrigation are much more sensitive to attack by biotic pests, especially foliar and root pathogens. Early detection can make the difference between financial profit and loss.
In summary, management of the bean crop is more difficult under limited irrigation. Conserve irrigation water for the critical growth periods of flowering and pod fill. Monitor every aspect of the crop to limit or reduce damage by pathogens, especially root pathogens. For further information, contact the author by phone at 970-491-6501 or via e-mail at mbrick@lamar.colostate.edu.
References:
1. Allen, R.G., C.D. Yonts, and J.L. Wright. 2000. pp 71-92. . In S. P.
Singh (ed.) Bean Research, Production & Utilization - Proc. of the
Idaho Bean Workshop Celebrating 75 Years of Bean Research &Development
and 50 Years of the Cooperative Dry Bean Nursery. Univ. of Idaho, ID.
2. Bandaranayake, M.W. 1990. Effects of soil moisture on growth and yield
of beans. M.S. Thesis. Colorado State University.
3. Yonts, C.D. 1996. Irrigation Requirements. pp. 24-26. In: Schwartz,
H.F., M.A. Brick, D.S. Nuland, and G.D. Franc (eds). Dry Bean Production
and Pest Management, Regional Bulletin No. 562A. Colo. State Univ. Ext.
and Agr. Exp. Sta., Ft. Collins, CO. 106 pp.
