WATER DEFICIT EFFECTS ON ROOT DISTRIBUTION OF SOYBEAN, FIELD PEA AND CHICKPEA

Authors: Benjamin, Joseph; Nielsen, David

Submitted to: Field Crops Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/15/2005
Publication Date: 6/1/2006
Citation: Benjamin, J.G., Nielsen, D.C. 2006. Water deficit effects on root distribution of soybean, field pea and chickpea. Field Crops Research. 97:248-253.

Interpretive Summary: Cropping diversity in the central Great Plains of the United States could be improved if suitable legumes were found to include in crop rotations. Several legumes that show promise for crop production are chickpea, field pea, and soybean. We conducted an experiment to examine how the root systems of these legumes responded to water stress by growing them either under natural rainfall conditions or growing them with sufficient supplemental irrigation to match evapotranspiration demand. We sampled the root distribution at nine inch depth intervals to a depth of 45 inches directly beneath the plants at the late bloom and mid pod fill growth stages for each species. Roots were washed free of soil and roots were separated from soil debris by hand. Root surface area measurements were made and root weights were recorded for each depth interval. Soybean had the greatest total root weight in the surface 45 inches of soil followed by chickpea and field pea. Total soybean root weight did not increase between the late bloom and mid pod fill growth stages but chickpea and field pea total root weights did increase between these growth stages. Chickpea had the greatest total root area density followed by soybean and field pea. There was no significant increase in total root surface area from the late bloom growth stage to the mid pod fill growth stage for the chickpea or field pea. Soybean total root surface area increased from the late bloom to the mid pod fill growth stages. The root surface area of the chickpea or field pea was similar whether irrigated or not. Irrigated soybean had greater total root surface area than soybean grown under dryland conditions. Field pea and chickpea had a greater proportion of their root systems deeper in the soil profile than soybean. Field pea and chickpea responded to drier soil conditions by increasing the proportion of roots deeper in the soil whereas soybean maintained the majority of the roots near the soil surface regardless of water stress. Field pea and chickpea had a greater root surface area to weight ratio than soybean, indicating more fine roots in the root system. Chickpea may be the best suited of these species for dryland crop production in Colorado due to an adaptive root distribution based on water availability and large root surface area per unit root weight.

Technical Abstract: Cropping diversity in the central Great Plains of the United States could be increased by including suitable legumes in crop rotations. Water is limiting to all crops grown in this region and agronomic crops frequently experience water deficit stress during their life cycle. Legumes that show promise for crop production in this region are chickpea (Cicer arietinum L.), field pea (Pisum sativum L.), and soybean (Glycine max L. Merr.). An experiment was conducted to examine legume root system response to water deficit stress. All three legumes were grown at two water regimes: under natural rainfall conditions and irrigated to minimize water deficit stress. We sampled the root distribution for each species at 0.23 m depth intervals to a depth of 1.12 m directly beneath the plants at the late bloom and mid pod fill growth stages. Roots were washed free of soil and were separated from soil debris by hand. Root surface area measurements were made and root weights were recorded for each depth interval. Water deficit did not affect the relative soybean root distribution. Approximately 97% of the total soybean roots were in the surface 0.23 m at both sampling times and under both water regimes. In contrast, water deficit stress resulted in a greater proportion of chickpea and field pea roots to grow deeper in the soil. Under irrigated conditions, about 80 % of the chickpea and field pea roots were in the surface 0.23 m. Under dry conditions, about 66 % of the total chickpea and field pea roots were in the surface 0.23 m and the remainder of the roots were deeper in the soil profile. Field pea had a root surface area to weight ratio (AWR) of 35 to 40 m2 kg-1, chickpea had a AWR of 40 to 80 m2 kg-1, whereas soybean had a AWR of 3 to 7 m2 kg-1, depending on plant growth stage. The greater AWR indicates a finer root system for the field pea and chickpea compared with soybean. From a rooting perspective, chickpea may be the best suited of these species for dryland crop production in semi-arid climates due to an adaptive root distribution based on water availability and large root surface area per unit root weight.