Research on alternative rice establishment practices has demonstrated the feasibility of drastically changing the way rice is grown in California to control herbicide-resistant weeds and to reduce herbicide use.

A study at the Rice Experiment Station has for five years examined five alternative stand establishment techniques. These systems highlighted shifts in weed populations and created opportunities to exploit weed recruitment by shifting establishment techniques after several years.

Alternative rice establishment demonstration - The plot located on the left side foreground is a completely untreated control. The plot immediately to the right of this plot is glyphosate burn down only. It yielded 7,600 pounds/acre. Other plots had follow-up foliar herbicide treatments applied to control weeds that germinated after the stale seedbed. No resistant watergrass germinated after the initial stale seedbed treatments.

Water-seeded treatments were shifted to drill seeding and drill-seeded treatments were shifted to water seeding. Rice establishment techniques developed and evaluated from 2004 through 2007 included conventional water seeding; conventional drill seeding; water seeding after spring tillage and a stale seedbed; water seeding after a stale seedbed without spring tillage; and drill seeding after a stale seedbed without spring tillage.

Water-seeded systems favored aquatic weeds, while dry or drill-seeded systems favored aerobic/dryland weeds. The stale seedbed technique, in which weeds are encouraged to germinate prior to elimination with a broad-spectrum herbicide like glyphosate (Roundup®), dramatically reduced weed pressure.

Plots from experiments in 2008 validate the potential for shifting aerobic and anaerobic stand establishment and the value of implementing a stale seedbed. In fields that had been managed with conventional water seeding, weeds were drastically reduced in these plots when rice was drill seeded following a stale seedbed. Plots heavily infested with barnyardgrass and sprangletop after four years of drill seeding rice were switched to water seeding after a stale seedbed with remarkable results. Weeds were almost absent from these plots as a result of the change in rice establishment method.

All this was achieved without any additional herbicides besides glyphosate. Alternating rice establishment systems from aerobic (dry seeding) to anaerobic (water seeding) following a stale seedbed technique allows for a major reduction of herbicide-resistant weed infestations in rice and overall herbicide use and associated costs.

Except for the rotation from conventional water seeding into a drill-seeded, no-till system, all rotations had the same yields in areas with conventional weed control or where the only weed control treatment was glyphosate. This demonstrates the value in a stale-seedbed treatment to control resistant weeds with glyphosate (or similar compound) for a brief period before returning to conventional rice-growing methods. The added bonus is a dramatic reduction in weed control inputs that year.

While drill seeding can be helpful in reducing aquatic weed pressure, its drawback is the potential for strong grass weed infestations and the potential for red rice contamination. Therefore, drill seeding should only be used in conjunction with a stale seedbed and should be implemented either before or after water-seeded rice that involves the use of a stale seedbed treatment with glyphosate.

Glenn County grower site

A Glenn County grower plagued by herbicide-resistant late watergrass (mimic) invited scientists to implement an alternative stand establishment technique on a 10-acre field. In spite of multiple herbicide applications over the years, he had failed to control mimic, causing heavy losses in his fields.

He decided to try the spring-tilled, stale-seedbed method, although he knew it might delay planting.  For that reason he chose a short-season variety, M-104. The key to success in this field was to allow substantial weed emergence prior to glyphosate application. He plans on implementing this approach on a larger area in 2009. His experience confirmed observations from the RES experimental plots and demonstrates the feasibility of implementing one of the alternative establishment methods under grower conditions to control a severe mimic problem.

Nitrogen use study

Another important objective of this project is to explore how alternative rice establishment systems may affect nutrient management. Nitrogen fertility trials were conducted for three rice establishment systems at the RES and at one farm site. Total nitrogen application rates in the study ranged from 0-200 pounds/acre in the form of urea. A treatment with ammonium sulfate was added due to grower interest. At both research sites there was no spring tillage.

Since these nitrogen fertility trials have been conducted only for one year, results are preliminary. Results from 2008 showed that splitting nitrogen applications had no significant impact on grain yields in all establishment systems studied. Total nitrogen applications split between preflood and mid-tillering produced yields similar to preflood-only applications. If a preflood application is sufficient, that would save the need for an additional field pass.

Nitrogen source had an impact on grain yield in only one establishment system. Ammonium sulfate treatments reduced grain yields significantly in the water-seeded, no-till stale-seedbed system compared to preflood urea treatments. Further tests will determine whether urea applications are best for this establishment system.

Yield response varied among systems. Water-seeded, stale-seedbed systems responded best to nitrogen applications between 150-200 pounds/acre, whereas the other three systems responded best to nitrogen applications between 100-150 pounds/acre. These results are consistent with previous years’ studies. The potential loss of nitrogen due to early-season, water-management practices and its impact on nitrogen fertility in these alternative systems warrants further research.