Water use of different weed species using lysimeter and NDVI

Weeds compete with agronomic crops for water, light, and nutrients, significantly affecting agricultural yields (Fialho et al., 2012; Swanton et al., 2015). According to Cirujeda et al. (2012), the infestation of Cyperus rotundus in tomato plantation was responsible for a 64% reduction in yield compared to the area without interference from this weed. Besides the competition for resources, weeds can cause other types of damage, such as the damage to mechanized harvesting, allelopathic effects, pest and disease hosting, changes in the secondary metabolism of crops, among others (Rockenbach et al., 2018). Given this scenario, it is evident that a greater understanding of the interactions between crops and weeds is of fundamental importance for developing more efficient and sustainable agriculture. Among the various existing species of weeds, Cyperus rotundus, Commelina diffusa, and Cynodon dactylon stand out because they are difficult to control and have an intense competition and dissemination capacity. According to Das (2008), Cyperus rotundus is present in the world’s tropical and subtropical regions, interfering in 52 crops in 92 countries. Commelina diffusa, on the other hand, for being tolerant to the herbicide glyphosate, has become a major problem with the advent of the transgenic technology Roundup Ready (RR) in different crops (Opeña et al., 2014). Cynodon dactylon, according to Johnson and Davis (2012), causes significant economic damage in organic plantations due to its high capacity to reproduce by rhizomes, stolons, and seeds, combined with the absence of efficient control compatible with organic production standards. Several studies demonstrate that weeds have greater development than agronomic crops in environments with limited resources (Berger et al., 2010; Opeña et al., 2014; Swanton et al., 2015). This occurs because, along with the genetic improvement of cultivated plants, the yield and quality of fruits were valued to the detriment of rusticity and edaphoclimatic adaptation (Bai et al., 2018). On the other hand, most spontaneous plants evolved through natural selection, developing several resistance mechanisms to adverse conditions in the environment, especially to water deficit in soil. Water is vital for several physiological processes in plants, such as respiration, photosynthesis, cell division, absorption, and transport of nutrients, among others (Berger et al., 2010). However, the dispute with other sectors for this resource has increased every day due to climate changes combined with poor management of its Abstract: Background: Weeds reduce water use efficiency in crops due to water used by the weed and to the reduction in crop yield. In addition to the usual presence of weeds in the interrow of different crops, the management of these plants has moved away from the idea of total control. Thus, the amount of water lost through the evapotranspiration of weeds (ETW) must be understood. Objective: Determine the water use and crop coefficient (Kc) of the weed species Commelina diffusa, Cyperus rotundus, and Cynodon dactylon using drainage lysimeters associate with the Normalized Difference Vegetation Index (NDVI). Methods: The experiment was carried out at the Lysimetric Station of the Federal University of Viçosa, in Viçosa-MG, in a randomized block design, with four treatments and four replicates. Reference evapotranspiration (ETo), necessary to calculate Kc, was obtained in situ through lysimeters cultivated with Paspalum notatum. Results: The highest Kc values were found in the final third of the experimental cycle, equal to 1.32, 0.93, and 0.90 for C. diffusa, C. rotundus, and C. dactylon, respectively. The NDVI showed a good correlation with Kc and biomass, with R2 ranging from 30.9 to 54.6% and from 46.1 to 63.1%, respectively. Accumulated ETW values ranged from 336 to 473 mm, with C. diffusa showing the highest water consumption, followed by C. rotundus and C. dactylon. Conclusions: C. diffusa has higher Kc and water consumption than C. rotundus and C. dactylon. NDVI can be used in the estimation of the Kc and biomass of weeds.