Economic Analysis of Weed-Suppressive Rice Cultivars in Flood- and Furrow-Irrigated Systems under Reduced Herbicide Inputs

Authors: WATKINS, KENTON - UNIVERSITY OF ARKANSAS; GEALY, DAVID; ANDERS, MERLE - UNIVERSITY OF ARKANSAS; MANE, JANJITSINH - UNIVERSITY OF ARKANSAS

Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/4/2018
Publication Date: 6/4/2018
Citation: Watkins, K.B., Gealy, D.R., Anders, M.M., Mane, J. 2018. Economic Analysis of Weed-Suppressive Rice Cultivars in Flood- and Furrow-Irrigated Systems under Reduced Herbicide Inputs. Weed Science. doi:10.1017/aae.2018.9.
DOI: https://doi.org/10.1017/aae.2018.9

Interpretive Summary: Weed control in rice is a constant challenge that is heightened with the increasing incidence of herbicide resistance among weed populations and the diminishing availability of irrigation water. Weed-suppressive rice varieties are known to produce acceptable grain yields while reducing the impacts from weeds under flood-irrigated systems, thus potentially allowing farmers to reduce herbicide use in some rice production systems. Use of furrow irrigation in rice, a practice in which the fields are never covered with a flood, is a promising, sustainable approach capable of reducing irrigation water usage as well as methane greenhouse gas emissions. In a three-year study, economic measures of rice production were evaluated for both weed-suppressive and non-suppressive varieties in flood- and furrow- irrigated rice under ‘low’, ‘medium’, and ‘high’ commercially-recommended herbicide application rates. The profits for each combination of irrigation type, variety, and herbicide rate were calculated as were the probabilities that increasing herbicide rates from the low to the medium rate or to the high rate would achieve an increased profit over and above that from using the low rate. Under flood irrigation, the weed-suppressive varieties ‘Rondo’ and ‘PI 312777’ were more profitable using medium rather than high herbicide rates, and thus achieved greater profitability using less herbicide as compared with the non-suppressive commercial rice varieties. In furrow irrigation, reducing herbicide rates in combination with weed-suppressive varieties was not practical because profits were maximized only when using the high herbicide rates. However, profitability in the furrow irrigation system was much greater for varieties with natural weed suppression abilities such as ‘PI 312777’ and ‘Rondo’, and a commercial hybrid variety compared with common non-suppressive commercial varieties such as ‘Wells’ and ‘Lemont’. Overall, this research has provided strong evidence that choosing a variety with weed-suppressive abilities could be an important key to improving the profitability of furrow-irrigated rice.

Technical Abstract: Weed-suppressive rice cultivars have been shown to produce commercially acceptable yields and reduce weed impacts under conventional flood-irrigated systems, and their use has been proposed as a potential means of reducing herbicide inputs in some rice production systems. Use of aerobic rice systems such as furrow irrigation and intermittent irrigation are potential approaches to reduce irrigation water usage and methane emissions. However, the comparative economics of using weed-suppressive cultivars in flood and aerobic systems have not been conducted. This study uses yield and herbicide application data from a three-year study evaluating both weed-suppressive and weed non-suppressive cultivars in flood- and furrow- irrigated rice under three different weed management levels (low, medium, and high herbicide inputs). Net returns to herbicide application were calculated, and Bayesian statistical analysis was used to calculate probabilities of exceeding target monetary gains from additional weed management beyond the low level. Economic results varied by irrigation treatment. Under flood irrigation, the weed-suppressive indica ‘Rondo’ and the allelopathic indica ‘PI 312777’ were more profitable using medium rather than high weed management and thus achieved greater profitability using less herbicide inputs relative to weed non-suppressive cultivars. In furrow irrigation, no opportunity to reduce herbicide inputs with weed-suppressive cultivars was evident, as returns were maximized using high rather than medium weed management. However, furrow system profitability appeared to be enhanced by cultivars exhibiting weed-suppressive ability. ‘PI 312777’ and ‘Rondo’, and a commercial hybrid produced much larger returns than weed non-suppressive commercial cultivars such as ‘Bengal’, ‘Lemont’, and ‘Wells’ in the furrow irrigation system.