Head Rice Quality 85

Head Rice Quality-85
Project Leader and Principal UC Investigators Shu Geng, Department of Agronomy and Range Science, University of California, Davis	Objective Head rice yields differ by variety, by year and by grain moisture content at harvest time. There has not been agreement regarding the potential importance of genetic control of head rice yields. One objective of this project was to determine the relationship between head rice yields and variety, location, and grain moisture content and temperature at harvest. Records from farm deliveries to the Rice Growers Association (RGA) and the Butte County Rice Growers Association (BUCRA) were used. A second objective was to determine by field experiments, if there were relationships between the development of panicles during grain filing and grain quality of different varieties. Head Rice and Total Rice Yields The 1984 data was based on 1,413 lots of rice delivered to RGA and BUCRA and on weather data from ten weather stations located in the rice growing regions of the Sacramento Valley. The weather data came from the National Oceanic and Atmospheric Administration-National Weather Service (NOAH). The average head rice percentage was 49.5, the lowest since 1979. There were large differences among varieties, with M-101 being the lowest at 40.7 percent and M-7 the highest at 60.7. Head rice yields also differed by location. The lowest was in the Stockton area at 36.8 percent and the highest was in the Orland area at 56.6 percent, but these differences reflected the varieties grown more than environmental differences. Total milled rice averages among varieties and locations were not significantly different. Moisture content of the grain at harvest was low at all locations except Orland and for all varieties except M-7. This probably accounts for the low head rice percentages, but a contributing factor was the general shift by growers to early maturing varieties. When cultivars were grouped by maturity from very early to late, the percentages of head rice, total milled rice and grain moisture content at harvest increased from early to late maturity. Locations with more than 30 percent of their lots of rice in the very early maturity class had head rice yields of less than 50 percent. A comparative analysis of 9,428 lots of rice showed that the very early and early varieties had the lowest head rice yields in 1984, while the intermediate and late varieties had head rice yields similar to 1983. Many more lots of very early and early varieties were delivered to the mills in 1984, and they were harvested over a longer period. Most of the rice was harvested at temperatures less than 90°F for the years 1979 through 1983, but in 1984, much of the rice was harvested at temperatures above 90°F. This made it possible to examine the effects of temperature at harvest. The very early varieties showed decreased head rice yields when temperatures at harvest exceeded 90°F. The intermediate and late varieties were remarkably insensitive to harvest temperature. Moisture content in the grain at harvest increased from 19.8 percent in 1983 to 23.2 percent in 1984 and head rice increased from 49.5 to 57.8 percent. It was estimated that a replacement of very early by early varieties could increase head rice 11 percent under 1984 conditions (from 41.0 to 52.4 percent). Both climatic and genetic effects on head rice were clearly demonstrated. Differences among varieties persisted in every environment for every year and between years, whether the environmental conditions were favorable or not. Panicle Development Studies Panicle lengths among six varieties differed, but there was no detectable relationship between panicle length and time of maturity. Panicle length may be related to some of the uniformity characteristics of the kernels. This is still to be investigated. Panicles reached maximum weight shortly before maturity. Time required for panicles to reach maximum weight ranged from 25 to 38 days from flowering. In general, the time required is related to the maturity class, with early types reaching maximum weight more rapidly than late types. Grain weights for kernels in the upper, middle and lower parts of the panicle showed that L-202, M-101, and M-201 were more sensitive to changes in the environment than S-201, M-302 and M-7. The more sensitive varieties had larger differences in grain weights among the three parts. Panicle characteristics may explain some of the differences in milling qualities among varieties. It follows that varieties selected for more synchronous development of panicles and of the kernels within the panicles may produce higher head rice yields.

Head Rice Quality-85

Project Leader and Principal UC Investigators

Shu Geng, Department of Agronomy and Range Science, University of California, Davis

Objective

Head rice yields differ by variety, by year and by grain moisture content at harvest time. There has not been agreement regarding the potential importance of genetic control of head rice yields.

One objective of this project was to determine the relationship between head rice yields and variety, location, and grain moisture content and temperature at harvest. Records from farm deliveries to the Rice Growers Association (RGA) and the Butte County Rice Growers Association (BUCRA) were used.

A second objective was to determine by field experiments, if there were relationships between the development of panicles during grain filing and grain quality of different varieties.

Head Rice and Total Rice Yields

The 1984 data was based on 1,413 lots of rice delivered to RGA and BUCRA and on weather data from ten weather stations located in the rice growing regions of the Sacramento Valley. The weather data came from the National Oceanic and Atmospheric Administration-National Weather Service (NOAH).

The average head rice percentage was 49.5, the lowest since 1979. There were large differences among varieties, with M-101 being the lowest at 40.7 percent and M-7 the highest at 60.7. Head rice yields also differed by location. The lowest was in the Stockton area at 36.8 percent and the highest was in the Orland area at 56.6 percent, but these differences reflected the varieties grown more than environmental differences.

Total milled rice averages among varieties and locations were not significantly different.

Moisture content of the grain at harvest was low at all locations except Orland and for all varieties except M-7. This probably accounts for the low head rice percentages, but a contributing factor was the general shift by growers to early maturing varieties.

When cultivars were grouped by maturity from very early to late, the percentages of head rice, total milled rice and grain moisture content at harvest increased from early to late maturity. Locations with more than 30 percent of their lots of rice in the very early maturity class had head rice yields of less than 50 percent.

A comparative analysis of 9,428 lots of rice showed that the very early and early varieties had the lowest head rice yields in 1984, while the intermediate and late varieties had head rice yields similar to 1983.

Many more lots of very early and early varieties were delivered to the mills in 1984, and they were harvested over a longer period. Most of the rice was harvested at temperatures less than 90°F for the years 1979 through 1983, but in 1984, much of the rice was harvested at temperatures above 90°F. This made it possible to examine the effects of temperature at harvest. The very early varieties showed decreased head rice yields when temperatures at harvest exceeded 90°F. The intermediate and late varieties were remarkably insensitive to harvest temperature.

Moisture content in the grain at harvest increased from 19.8 percent in 1983 to 23.2 percent in 1984 and head rice increased from 49.5 to 57.8 percent. It was estimated that a replacement of very early by early varieties could increase head rice 11 percent under 1984 conditions (from 41.0 to 52.4 percent).

Both climatic and genetic effects on head rice were clearly demonstrated. Differences among varieties persisted in every environment for every year and between years, whether the environmental conditions were favorable or not.

Panicle Development Studies

Panicle lengths among six varieties differed, but there was no detectable relationship between panicle length and time of maturity. Panicle length may be related to some of the uniformity characteristics of the kernels. This is still to be investigated.

Panicles reached maximum weight shortly before maturity. Time required for panicles to reach maximum weight ranged from 25 to 38 days from flowering. In general, the time required is related to the maturity class, with early types reaching maximum weight more rapidly than late types.

Grain weights for kernels in the upper, middle and lower parts of the panicle showed that L-202, M-101, and M-201 were more sensitive to changes in the environment than S-201, M-302 and M-7. The more sensitive varieties had larger differences in grain weights among the three parts.

Panicle characteristics may explain some of the differences in milling qualities among varieties. It follows that varieties selected for more synchronous development of panicles and of the kernels within the panicles may produce higher head rice yields.