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ARS Home » Southeast Area » Tifton, Georgia » Crop Protection and Management Research » Research » Publications at this Location » Publication #318978

Title: Palmer amaranth (Amaranthus palmeri) competition for water in cotton

Author
item BERGER, S - University Of Florida
item FERREL, J - University Of Florida
item ROWLAND, D - University Of Florida
item Webster, Theodore

Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/10/2015
Publication Date: 10/1/2017
Citation: Berger, S.T., Ferrel, J.A., Rowland, D.L., Webster, T.M. 2017. Palmer amaranth (Amaranthus palmeri) competition for water in cotton. Weed Science. 63(4):928-935.

Interpretive Summary: Weed species compete primarily with crops for light, water, and nutrients; it is proposed that water is the most critical of all plant growth requirements. Palmer amaranth is a C4 summer annual native to the Sonoran Desert in the southwestern United States and neighboring regions of Mexico. Many adaptations allow the plant to be successful in a desert environment, particularly its ability to respond quickly to intermittent desert rainfall through season-long seed emergence and rapid initial growth rate. Though the potential for cotton yield loss due to Palmer amaranth competition is well documented, little work has been done to determine the basis for this competition. Average water use was almost three times higher for Palmer amaranth than weed-free cotton. Cotton plants typically grow uniformly, causing lower leaves to become shaded as biomass increases, with reductions in photosynthesis in older/shaded leaves. Conversely, Palmer amaranth plant architecture minimizes self-shading, with more photosynthetically efficient leaves occurring at all levels of the canopy throughout the season. Palmer amaranth produces shallow and widespread root structure to effectively harvest the limited rainfall quickly near the soil surface. In well-watered conditions, Palmer amaranth has the potential to form more roots of smaller diameter, thereby giving Palmer amaranth access to a larger soil volume to mine water and nutrients. In drought situations similar to 2011, the soil water profile is likely to be depleted by both the cotton and Palmer amaranth roots. However, the shallow Palmer amaranth roots are then poised to rapidly absorb rainfall or irrigation that wets only the shallow soil depths. Palmer amaranth’s region of influence extended to 1 m in depth and 2.4 m laterally. In times of excess water availability, even though Palmer amaranth removes more than twice as much water per day as cotton, soil moisture is quickly recharged and cotton plants do not become water stressed. In these situations, yield losses to Palmer amaranth competition are likely due to other factors, such as light competition within the canopy.

Technical Abstract: Palmer amaranth is a troublesome weed in cotton production. Yield losses of 65% have been reported due to season-long Palmer amaranth competition with cotton. To determine if water is a factor in this system, experiments were conducted in 2011, 2012, and 2013 in Citra, FL and in Tifton, GA. In 2011, infrequent rainfall lead to drought stress. The presence of Palmer amaranth resulted in decreased soil relative water content up to 1 m in depth. Cotton stomatal conductance (gs) was reduced on plants up to 1.8 m from a Palmer amaranth plant. In 2012 and 2013 higher than average rainfall resulted in excess water throughout the growing season. In this situation, no differences were found in soil relative water content or cotton gs, as a function of proximity to Palmer amaranth. A positive linear trend was found in cotton photosynthesis and yield; each parameter increased as distance from Palmer amaranth increased. Even in these well-watered conditions, daily water use of Palmer amaranth was considerably higher than that of cotton, at 1.2 and 0.49 g H20 cm-2day-1, respectively. Palmer amaranth removed more water from the soil profile, yet rainfall was adequate to replenish the profile.