Field and laboratory experiments

Rice varieties M-202, M205, and M-206 were planted in a series of hydraulically isolated basins at the Rice Experiment Station. Each basin was equipped with water intake and drain outlets. The individual drains and physical separation of these experimental plots allowed for discrete drain times to be imposed without compromising soil water status from the lateral movement of water between basins. Irrigation water was supplied from a common feeder ditch.

Field preparation, fertility and pest management followed standard Rice Experiment Station (RES) practices. The experiment was planted June 5. Seeds were dry planted at a rate of 150 pounds/acre. Irrigation water was brought to a depth of three to four inches during germination and seed establishment. A low fertilization rate was used because of the late planting date.

Each variety was subjected to four different drain dates: 12, 16, 20, and 24 days after 50% heading. Fifty percent heading occurred September 1 for M-202, September 2 for M-205, and August 29 for M-206. All basins were harvested on October 22, 26, 29, and November 4.

Environmental conditions were monitored during the experiment from four weeks prior to the first harvest date to the last harvest date. Relative humidity and leaf wetness sensors were deployed at canopy level in all plots. Soil moisture probes were installed six inches below soil surface. Two meteorological stations also tracked conditions. Single kernel moisture measurements were taken every morning and late in the afternoon, starting when kernel moisture content reached 26% and continuing until the end of the harvest period.

In addition to the RES experiment, samples of M-202, M-205, and M-206 were collected from statewide variety trials near Butte City and Natomas. These plots were harvested at several dates to obtain a range of harvest moisture content. Samples were threshed, dried, and evaluated with the same procedure used at RES.

Within each variety, the rate of kernel drying below 25% moisture content was similar at all drain dates. The rate of moisture loss across varieties averaged 0.8% per day. M-206 showed the least variability in kernel moisture content in relation to drain dates. Surprisingly, drain date did not affect the rate of kernel dry down or the time required to reach harvestable moisture content.

Overall, yields were low, presumably in response to the late planting and the modest amounts of fertilizer applied. The yield of M-206 proved to be the least sensitive to delayed planting. On the whole, yields increased as the drain date was delayed. There was no apparent “leveling off” of the yield trends, suggesting that optimal drain date for maximum yield may be longer than 24 days after heading. Based on this year’s results – and those from previous years’ research – draining is not advised sooner than 20 days after heading.

To varying degrees, total rice yield and head rice yield of all varieties increased with later drain dates. Total rice yields of M-202 and M-206 were similar and less affected by early drain dates than M-205. Head rice yield trended higher at later drain dates for all varieties.

All three varieties showed comparable sensitivity to environmental conditions during agronomic maturity when rice was drying down to a harvestable moisture level. Observed differences in head rice yield were not found to be associated with reduced soil moisture content. The impact of water-limited conditions (i.e. an early drain) on rice quality occurs when the grain is above 27% moisture content. Differences in yield and quality are not attributable to drain times during the latter stage of grain maturation.

The productivity of the three test varieties may be adversely affected by the loss of flooded conditions. Yield and grain quality are compromised when the soil transitions from an anaerobic to an aerobic state. Preliminary results from trials at the RES in 2009, where rice was grown under well-watered but non-flooded conditions, resulted in delayed development and reduced yield.

Prior years’ research indicated that M-205 and M-206 could be drained at 20 days after heading while maintaining quality and yield. In contrast, 2009 results suggest that draining 24 days after heading or longer would be best. The estimated end-of-season average water use is about a half inch per day. Thus, further testing is necessary to more accurately calculate potential water savings from earlier drain times.

Storage insect monitoring

Two rice storage facilities were surveyed for the presence of seasonal insects that could potentially affect rice quality.

In Richvale a flat bed storage warehouse containing 20 million pounds of rough rice was surveyed. In Arbuckle, a flat bed storage warehouse with 45.5 million pounds of rough rice and a silo containing 8 million pounds of rough rice was surveyed. Three types of traps were used: pheromone traps, probe traps, and dome traps.

Seventeen species were identified. Two are internal feeders, four external feeders, five feed on fungi, two feed on grain dust or fungi, and one is predaceous. The most abundant insect in the warehouses was the Angoumois grain moth, caught in the pheromone and probe traps. In the silo the red flour beetle, an important pest of stored grains, was the most abundant. The lesser grain borer, a severe pest of stored rice, was found at relatively low densities in all locations. Other insects collected are not considered important pests of stored rice or feed on fungi developing on the grain. Their presence may indicate that storage conditions need to be improved.