Weed Community Dynamics and System Productivity in Alternative Irrigation Systems in California Rice

Abstract

Over the last 10 yr, California has experienced a series of ever-worsening droughts. Rice, traditionally a flooded crop, has come under increasing scrutiny with respect to its water use, leading to proposals to evaluate alternative irrigation systems. For growers, weed competition is one of the most limiting factors to maintaining high yields, so understanding the shifts among species in weed communities under the proposed alternative irrigation systems is vital. A field study was conducted from 2012 to 2014 to compare weed population and growth dynamics with three irrigation systems: (1) a conventional water-seeded control system (WS-Control), with a permanent flood of 10 to 15 cm from planting until 1 mo prior to harvest; (2) a water-seeded alternate wet and dry system (WS-AWD), with the field flooded from planting until canopy closure, after which floodwater was allowed to subside and the field was reflooded when the soil volumetric water content reached 35%; and (3) a drill-seeded alternate wet and dry system (DS-AWD), with rice drill seeded and then flush irrigated to establish the crop, after which the field was flooded until canopy closure and then underwent an alternate wet and dry (AWD) treatment similar to WS-AWD. In the AWD treatments, there were two drying periods, neither of which occurred after the heading stage. The dynamics of major weed species were evaluated using plant density counts (2012) and relative cover and biomass (2013 and 2014). Grasses (sprangletop and watergrass species) dominated the DS-AWD system; sedges, broadleaves, and grasses dominated both WS systems. The WS-AWD system increased smallflower umbrella sedge relative cover at canopy closure, relative dry weight at harvest, and percent frequency when compared with the WS-Control system. Yields did not differ across treatments when weeds were controlled (P > 0.05); in the absence of herbicides, yields in the WS-AWD were equivalent to the WS-Control (ranging from 40 to 65% of the herbicide-treated yields) and zero in the DS-AWD due to weed pressure. Nomenclature: bearded sprangletop, Leptochloa fusca (L.) Kunth N. Snow; ducksalad, Heteranthera rotundifolia (Kunth) Griseb.; redstem, Ammannia coccinea Rottb.; ricefield bulrush, Schoenoplectus mucronatus (L.) Palla; smallflower umbrella sedge, Cyperus difformis L.; rice (Oryza sativa L.).

Emergence and early growth of multiple herbicide–resistant and -susceptible late watergrass (Echinochloa phyllopogon)

“…When comparing the average of the two populations, there was variation between treatments, with significantly less emergence occurring in the continuously flooded treatment compared to the intermittent flush and daily flush treatments (Figure 3), although differences were not significant between populations. This is consistent with field data with watergrass species, where shifting irrigation to flooding can be used to suppress watergrass populations (Brim-DeForest et al 2017;Pittelkow et al 2012). It is also consistent with the emergence data reported by Boddy et al (2012a), where both flooding and intermittent irrigation reduced emergence of both HR and RD populations.…”

“…Koss; synonym Echinochloa oryzicola Vasinger) is one of the most competitive weeds in the California rice agroecosystem, reducing yields up to 59% when uncontrolled (Gibson et al 2002). Recent data suggest that losses may be higher in dry-seeded systems (Brim-DeForest et al 2017). In California, late watergrass germinates and emerges under both aerobic and anaerobic conditions (Boddy et al 2012a;Linquist et al 2008;Pittelkow et al 2012).…”

“…Application of the late watergrass PBTM emergence model (Boddy et al 2012a) in the field for the susceptible (HR[S]) biotype failed to accurately predict emergence (Brim-DeForest et al 2014). Two significant factors may have contributed to the lack of fit: the assumption that seeds emerged from a normal distribution of soil depths and the assumption that early emergence was driven solely by temperature, not moisture.…”

Disentangling Challenges to Scaling Alternate Wetting and Drying Technology for Rice Cultivation: Distilling Lessons From 20 Years of Experience in the Philippines

“…On the other hand, AWD can increase weed density (Figure 4D) if farming practices are not coupled with appropriate weed management interventions (Brim-DeForest et al, 2017;Samoy-Pascual et al, 2020). Some studies done in Nepal reported that AWD restricts the proliferation of weeds due to its soil contraction effects (Howell et al, 2015).…”

Effects of herbicide management practices on the weed density and richness in dicamba-resistant cropping systems in Indiana

“…Weed management practices impose selection pressures that drive shifts in weed communities. Documented cases of weed shifts due to changes in weed management have occurred as a result of tillage, irrigation systems, herbicide use, and crop rotation (Brim-DeForest et al 2017;Davis et al 2009;Johnson and Coble 1986;Johnson et al 2009;Menalled et al 2001;Tuesca et al 2001). Shifts in weed species have also been observed when comparing glyphosate-resistant cropping systems with conventional herbicide systems.…”