Evapotranspiration of Palmer amaranth (Amaranthus palmeri) in maize, soybean, and fallow under subsurface drip and center-pivot irrigation systems

Abstract

Palmer amaranth (Amaranthus palmeri S. Watson) is a major biotic constraint in agronomic cropping systems in the United States. While crop-weed competition models offer a beneficial tool for understanding and predicting crop yield losses, within these models, certain weed biological characteristics and their response to the environment are unknown. This limits understanding of weed growth in competition with crops under different irrigation methods and how competition for soil moisture affects crop growth parameters. This research measured the effect of center-pivot irrigation (CPI) and subsurface drip irrigation (SDI) on the actual evapotranspiration (ET a ) of A. palmeri grown in maize (Zea mays L.), soybean [Glycine max (L.) Merr.], and fallow subplots. Twelve A. palmeri plants were alternately transplanted one meter apart in the middle two rows of maize, soybean, and fallow subplots under CPI and SDI in 2019 and 2020 in southcentral Nebraska. Maize, soybean, and fallow subplots without A. palmeri were included for comparison. Soil moisture sensors were installed at 0-0.30, 0.30-0.60, and 0.60-0.90-m soil depths next to or between three A. palmeri and crop plants in each subplot. Soil moisture data were recorded hourly from the time of A. palmeri transplanting to crop harvest. The results indicate differences in A. palmeri ET a between time of season (early-, mid-, late-season) and crop type across 2019 and 2020. Although irrigation type did not affect subplot data, the presence of A. palmeri had an impact on subplot ET a across both years, which can be attributed to the variable relationship between volumetric soil water content (VWC) and ET a throughout the growing season due to advancing phenological stages and management practices. This study provides important and firstly established baseline data and information about A. palmeri evapotranspiration and its relation to morphological features for future use in mechanistic crop-weed competition models.