Alternative rice establishment

Alternative rice establishment practices developed at the Rice Experiment Station (RES) were tested in grower fields in 2009 to determine their feasibility for full-scale rice production.  

The majority of these systems involve the spring-tilled, stale seedbed technique.  Following spring tilling and rolling, fields are flushed with water prior to planting to encourage germination of watergrass, barnyardgrass, sprangletop, and smallflower umbrellasedge. These weeds are then treated with glyphosate (Roundup®), which provides control of all herbicide-resistant weed biotypes that can infest California rice fields.  To avoid delays in planting rice, late-season germinating weeds or those requiring longer and near-anaerobic flooding for germination, are not targeted by this technique.

Following this treatment the field is flooded and seeded without any additional tillage. Control of established weeds was complete and few grasses emerged later in the season.

Follow-up herbicide combinations were tested in an imbedded trial with excellent seasonal control of weeds and good yields. Although slight-to-moderate yield reductions were observed, this method of stand establishment is intended primarily to reduce resistant late watergrass over time. The longer-term goal is to rotate these fields back into more conventional systems with lower weed populations and exceptional yields.

The promise of this approach was demonstrated on the Glenn County farm tested first in 2008. A 10-acre site had far fewer grasses germinate in 2009 with the flushing technique. The research site was doubled in size. By midsummer, control of watergrass was in the low 90% range, while control of sprangletop was nearly 100%. Highest yields in a test plot set up within this field were in the 8,000 pounds/acre to 9,000 pounds/acre range when the glyphosate application was followed at the three-leaf stage of rice by Super Wham® (propanil), Granite® SC, or Regiment®. The untreated control yielded 2,000 pounds/acre, while the glyphosate-only treatment yielded 7,800 pounds/acre.

At the same farm, a fall-tilled, no spring-tilled field subjected to a stale-seedbed treatment did not yield as well. Although not as many rice weeds emerged, stand establishment was not as good in the spring-tilled field. Yields ranged between 4,300 pounds/acre and 5,600 pounds/acre. Two other cooperating growers using the spring-tilled, stale seedbed method had similar results in control of grasses and sedges.

Nutrient management

Nitrogen fertility trials in connection with alternative rice establishment techniques were conducted in 2008 and 2009 at the Rice Experiment Station and at four on-farm locations. Nine nitrogen treatments were applied at each site with rates ranging from zero to 200 pounds/acre. Urea and ammonium sulfate were both tested as nitrogen sources.

Grain yields from 2008 at the RES indicated that the wet-seeded conventional system reached maximum yields at nitrogen rates of 100 pounds/acre and above, while both stale seedbed systems appeared to require 150 pounds/acre or more to achieve maximum yields.

This may be partially explained by soil nitrogen dynamics. Soil mineral nitrogen concentrations at the RES indicate that preseason losses are highest in conventional systems, yet more soil nitrogen is mineralized after permanent flood (compared to stale seedbed systems). This increase in soil nitrogen may reduce the need for applied fertilizer, especially during critical early season growth. Higher nitrogen requirements in stale seedbed systems may be related to decreased soil nitrogen mineralization. Further research is required to determine the role of tillage in the nitrogen dynamics of alternative systems.

The highest yields in wet-seeded, stale seedbed systems at the RES and on-farm sites occurred at nitrogen applications of 200 pounds/acre. Yields for preflood and split nitrogen applications were similar in each system regardless of rate at the RES and at three of the four on-farm sites.

At the RES, urea proved to be a better source of nitrogen for stale seedbed systems than ammonium sulfate, which yielded 500 pounds/acre lower than other preflood nitrogen treatments of 100 pounds/acre. The four on-farm sites, which were all water-seeded, stale seedbed systems, exhibited similar trends with slightly lower nitrogen responses than the RES.

 Preflood nitrogen applications of 100 pounds/acre produced yields similar to higher nitrogen rates, but split rates of 25–75 pounds/acre produced significantly lower yields at three of four grower sites. Preflood and split nitrogen applications within the 150–200 pounds/acre treatments had equivalent yields.

Ammonium sulfate treatments performed better in growers’ fields. They did not produce significantly different grain yields than the urea treatments at three of four on-farm locations.

Nitrogen management in alternative systems

• Minimum tillage, stale seedbed establishment systems have higher nitrogen fertility requirements than conventional water-seeded systems.

• Alternative systems respond to nitrogen rates between 150 and 200 pounds/acre, depending on seeding practices and location.

• Urea appears to be a more reliable nitrogen source than ammonium sulfate, and may be more desirable because of higher nitrogen and ease of application.

• A single nitrogen application prior to permanent flood is sufficient to meet nitrogen fertility needs in alternative systems.