Economics of weed suppressive rice cultivars in flood- and furrow-irrigated systems

Authors: WATKINS, KENTON - University Of Arkansas; Gealy, David; ANDERS, MERLE - Retired Non ARS Employee; MANE, RANJIT - University Of Arkansas

Submitted to: Rice Technical Working Group Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 3/1/2016
Publication Date: 7/2/2017
Citation: Watkins, K.B., Gealy, D.R., Anders, M.M., Mane, R.U. 2017. Economics of weed suppressive rice cultivars in flood- and furrow-irrigated systems. 36th Rice Technical Working Group Meeting Proceedings, Galveston, TX, p. 106. March 1-4, 2016. CDROM.

Interpretive Summary:

Technical Abstract: Weeds are a major constraint to rice production. In the U.S, weeds in rice are controlled primarily with synthetic herbicides. Intensive herbicide application in rice also has many potential drawbacks, resulting in environmental pollution, human health concerns, and development of weed resistance. Because of these shortcomings, many have proposed the use of weed suppressive or allelopathic rice cultivars to reduce heavy dependence on synthetic herbicides. Water is also a constraining input in rice production and is becoming more limiting in many areas in the U.S. where rice is grown. In Arkansas, groundwater is the primary irrigation source for rice, and groundwater levels are declining in much of Arkansas due to continued withdrawals at pumping rates that are unsustainable. Concerns about groundwater depletion have prompted rice producers to consider production systems that use less water. One such system is furrow irrigation. Weed management in furrow irrigation is inherently challenging. Prolonged moist conditions under furrow irritation allow several terrestrial weeds normally controlled by flood to emerge. Weed suppressive cultivars may be beneficial for aerobic rice systems like furrow irrigation. An economic analysis of both weed-suppressive and weed non-suppressive rice cultivars under flood and furrow irrigation was conducted using yield and herbicide application data from a weed suppressive cultivar study conducted during the years 2009, 2010, and 2011 at Stuttgart, Arkansas. Net returns to herbicide application were calculated as gross returns less herbicide costs for each cultivar-irrigation-herbicide level combination. Herbicide levels were classified as “low,”, “medium,” and “high” herbicide intensity. Generally speaking, “low” corresponded to extremely low herbicide inputs that were well below recommended rates and intended to result in excessive weed competition against rice; “medium” and “high” corresponded to University recommendations, with “medium” providing less than optimal weed control (i.e. limited herbicide applications at rates recommended for lightly infested fields), and “high” representing maximum rates of one or more herbicides expected to provide excellent control in heavily infested fields. Barnyardgrass (Echinochloa crus-galli) and other grass weeds were the primary species targeted for control. The study also employed Bayesian statistical analysis to calculate probabilities of monetary gains for additional herbicide application beyond the “low” herbicide level. Probabilities of exceeding target monetary gains were calculated by rice cultivar and irrigation treatment for “medium” and “high” herbicide intensity relative to “low” herbicide intensity. The cultivars evaluated in the study included two weed suppressive cultivars (“Rondo” and the allelopathic cultivar “PI 312777”), a commercial hybrid (“CLXL729”), and four other weed non-suppressive varieties (“Bengal,” “Wells,” “Lemont,” and “CL171AR”). CLXL729 and CL171AR were included as standards for weed-suppression and yield, but were managed without the use of imidazolinone herbicides (i.e. not in a “Clearfield” system), which was the same as for all of the other cultivars. Interpretation of cultivar net returns to herbicide application varied depending on water management. Under flood irrigation, net returns for Rondo and PI 312777 were highest on average under medium herbicide intensity, while net returns for all other cultivars evaluated (CLXL729, Bengal, Wells, Lemont, and CL171AR) were highest on average under high herbicide intensity. Net return variability, as measured by the coefficient of variation, was correspondingly lower for Rondo and PI 312777 under medium herbicide intensity and lower for all but one of the other five cultivars evaluated under high herbicide intensity. Bengal was the one exception. Bengal had higher average ne