|Variety Trials - 96
Project Leader and Principal UC Investigators
James E. Hill, Extension Agronomist and Chair, Department of Agronomy and Range Science, UC Davis
Timothy J. Kesselring, Post Graduate REsearcher, Department of Agronomy and Range Science, UC Davis
John F. "Jack" Williams, UC Cooperative Extension Farm Advisor Sutter/Yuba counties
Steven C. Scardaci, UC Cooperative Extension Farm Advisor Colusa/Glenn/Yolo counties
C. Mick Canevari, UC Cooperative Extension Farm Advisor San Joaquin County
Randall "Cass" Mutters, UC Cooperative Extension Farm Advisor Butte County
|During 1996 University of California scientists in cooperation
with public and private plant breeders conducted 16 rice variety evaluation trials on
farms throughout the rice growing region of the state. Six similar tests, including two
from each maturity group, were conducted at the Rice Experiment Station at Biggs. Although
several advanced and preliminary breeding lines showed some improvement in yield or other
agronomic characteristics, most were at or below existing commercial varieties.
Researchers say this demonstrates the difficulty in achieving greater yield advances. For
example, M-202 was the highest yielding variety in the very early test and six of the top
10 yielding entries in the early test were already commercial varieties. In the late test
the top experimental and commercial cultivars were early types.
Rice scientists working on this project also examined ways to improve cultural practices. One study examined the effect of rice straw removal on potassium fertility. Another examined the effects of different nitrogen rates on two important Japanese varieties. A third study is examining the effect of different nitrogen and potassium rates on disease incidence. A fourth study is examining the effect of different straw management alternatives on rice production. Several other experiments conducted in cooperation with other investigators received assistance with planting, fertilizing, herbicide application, harvesting and data analysis from this project. This section reports significant findings from the 1996 variety trials.
Very Early Maturity
Nine advanced breeding lines and 11 commercial varieties were compared in four very early tests (less than 90 days to 50 percent heading). Eighteen preliminary lines were compared to the standards L-204 and the Japanese variety Akitakomachi at each location. Advanced lines at each location included 11 entries from the RES breeding program.
Grain yields in the advanced tests average 9,390 pounds/acre at Biggs, 8,490 pounds/acre at San Joaquin, 8,220 pounds/acre at Sutter, and 9,400 pounds/acre at Yolo. Over the four locations the highest yielding entry was M-202, which ranked first, second and fourth in yield at Sutter, Yolo and San Joaquin, respectively. Entry 92-y-624, an advanced medium-grain, was the second highest yielding entry at Sutter and ranked second in the four-location summary. Other commercial varieties ranking in the top ten included M-204, L-204, S-102 and M-201.
Nine advanced lines and nine commercial varieties were compared in four early tests (90-97 days to 50 percent heading). Twenty-three preliminary lines were compared to L-204 in separate tests at each location.
Test yields in the advanced lines, which included nine entries from the RES breeding program, averaged 9,240 pounds/acre at the Rice Experiment Station, 8,080 pounds/acre at Butte, 9,170 pounds/acre at Colusa and 6,850 pounds/acre at Yuba. The medium- grain cultivar 94-y-615 exceeded 10,000 pounds/acre at RES and Colusa and was the highest yielding entry over the four locations. Other leading entries included M-201, 92-y-624 and S-202. L-204, released in 1995, yielded 8,300 pounds/acre and ranked eleventh.
Six advanced lines and six commercial varieties were compared in three intermediate-late tests (more than 97 days to 50 percent heading). Twenty-four preliminary lines were also evaluated in separate tests at each location.
Average test yields in the advanced lines, which included six from RES breeders, were 9,440 pounds/acre at RES, 8,370 pounds/acre at Glenn and 7,520 pounds/acre at Sutter. An advanced medium grain, 94-y-416, was the highest yielding entry at Sutter and second at the RES and Glenn and was first in the over-location summary. M-204 produced higher yields than M-202 at each location. A-301, an aromatic long grain, ranked third overall, while premium quality M-401 ranked much lower.
Straw Management and Potassium
Researchers designed an experiment at the Rice Experiment Station to explore the relationship between various straw management alternatives and potassium fertility. Straw treatments included burning, incorporating, rolling and removal by baling under wither flooded and non-flooded conditions. Various rates of potassium up to 120 pounds/acre were superimposed over each straw management subplot. With no supplemental potassium, removal of rice straw by baling caused recognizable signs of potassium deficiency and significantly lower yields. Where straw remained in the field or was burned researchers found no significant differences between potassium rates, indicating that as long as the straw or ash remained in the field potassium deficiency did not occur. However, removal of straw containing potassium resulted in potassium deficiency.
Japanese Varieties and Nitrogen
California rice growers are increasingly interested in growing specialty varieties for both domestic and export markets. Japanese varieties can bring significantly higher prices if they maintain desirable grain quality characteristics, such as low protein and high amylose content. However, the high rates of nitrogen typical of those normally used for California rice may not bring out these grain characteristics and may, in fact, lead to excessive lodging. Research in Japan indicates that small amounts of nitrogen applied at the appropriate growth stage is the key to high grain quality. This experiment was designed to test the optimal rate and timing of nitrogen application to maximize yields and maintain the desired grain quality characteristics in two Japanese varieties, Akitakomachi and Koshihikaii.
Three experiments, each consisting of 21 nitrogen treatments, were established in grower fields. One field had a cropping history of Japanese rice, another field was coming out of a one-year fallow and the last had previously been planted in a standard California medium grain variety. Koshihikari was planted in one of these fields; Akitakomachi in the other two. Ammonium sulfate up to 100 pounds/acre was applied either preplant or at distinct stages of plant development - panicle initiation, pollen maturation and/or heading. Researchers monitored plant growth and development throughout the season, measured light penetration through the canopy, weighed final yield and analyzed grain for desired characteristics. They also used a hand-held chlorophyll meter to measure leaf nitrogen levels.
At this time, complete information is available only for the Akitakomachi experiment. Preliminary results indicate that yields were highest with preplant nitrogen at the 80 pound/acre rate. This rate also produced relatively high levels of amylose and scored well in taste tests. However, the best grain quality was observed with preplant nitrogen at the 60 pound/acre rate. A complete analysis of this study will be reported next year.
A 75-acre rice straw management trial was established near Maxwell in the fall of 1993. A similar 25-acre trial was established at the Rice Experiment Station in 1994. Researchers examined straw burning, incorporation, rolling and removal by baling under both winter flooded an unflooded conditions.
Straw treatment effects on yield were evident at both sites, although those results were not consistent across sites or in individual years. Yields were lower in the straw removal treatment in both years at the Biggs site. However, researchers say lower yields in this treatment are most likely due to potassium deficiency. Deficient soil nitrogen may also be a factor.
At the Maxwell site, straw treatment effects varied from year to year. Water salinity levels affected yields in 1994 but showed no differences among treatments. In 1995 herbicide damage affected seedling vigor in the burned and baled plots. In all years straw management demonstrated a significant effect on weed control at this site. Barnyard- grass and watergrass control was better in the burned and baled plots than in the incorporated or rolled plots. In 1996 the unflooded, incorporated plots showed a significant impact on yield.
Potassium, Nitrogen and Disease
Limited prior research suggests that in potassium deficient soils, potassium fertilization may reduce disease levels. This study sought to determine how the rate and timing of potassium fertilization affects disease incidence and other agronomic factors.
Very low soil potassium levels and a history of high disease incidence characterized the Yuba County rice field where the experiment took place. Yield form the previous two seasons was extremely low. In this experiment added potassium decreased stemrot incidence and aggregate sheathspot severity. However, significant interactions between these diseases take place with varying levels of nitrogen. The effect of additional potassium against stemrot incidence is more pronounced at lower nitrogen levels.
Additionally, split applications were more effective against stem rot than aggregate sheathspot. Extra nitrogen, across all potassium treatments decreased yield but increased grain moisture, plant height, lodging and stemrot incidence and severity. Aggregate sheathspot decreased with added nitrogen.
Other observations from his replicated trial showed:
From leaf analysis data in this experiment researchers conclude that current plant tissue guidelines are adequate; excess nitrogen can intensify a potassium- deficient situation; potassium fertilization is beneficial in reducing disease levels, particularly stem rot, in potassium- deficient soils; and split or top-dressed applications may be more efficient in terms of yield and disease impact than preplant applications. Researchers caution, however, that this is not evidence that potassium fertilization will have an impact on disease levels in soils that are not potassium deficient. Growers should use potassium as a fertilizer, not as a disease control material, and only when there is a demonstrated deficiency.