Head Rice Quality - Objectives

• Obtain field data under farm conditions on head rice yields over a period of years to determine trends in head rice yields and reasons for them.
• Compare the influence of varieties, fertilizer practices and drainage times on head rice yields.
• The ultimate goal is to develop and implement management practices that can improve head rice yield.

A decline in head rice yields as growers shift to earlier maturing varieties has fostered interest in research on whether lower head rice yields are the inevitable result of growing earlier maturing varieties. Experiments on head rice yields began in 1984.

Data obtained in 1985 and earlier established that: 1) varieties differed significantly in head rice yields, with early maturing varieties having lower head rice yields than later maturing varieties; 2) grain moisture content at harvest time was an important but not the only factor affecting head rice yields; and 3) climatic and genetic factors must be considered together in any program to improve head rice yields.

Studies in 1986 confirm previous results and have made a good start toward understanding the environmental, morphological and physiological factors affecting head rice yields. Only partial results are reported on the comparison of varieties and management practices because of the large amount of data still to be processed. These results will be reported next year. The data will be the basis for a computer management program to improve head rice yield.

Seven years of data (1979-1985) from 2,234 rice lots delivered to the Butte County Rice Growers Association show that head rice yields are clearly influenced by maturity groups. The overall averages for very early, early, intermediate and late varieties are 52, 53.8, 55.2 and 57.4 percent, respectively. Also during this seven-year period, there has been decline in head rice yields from 55.9 percent in 1979 to 51.5 percent in 1985, but year to year variations are quite large. The decline is explained by growers shifting to earlier maturing varieties.

Effects of moisture content of the grain at harvest on head rice cannot be completely generalized, as there are varietal differences. Most varieties show that the lower side of the optimum range of moisture content is from 21 to 23 percent for good head rice yields. The long-grain variety L-202 has a narrow range of desirable moisture content at harvest. The optimum moisture content at harvest was between 18 and 20 percent, and head rice yields declined sharply above and  below this narrow range. Head rice  yields for S-201, and L-202 at various moisture contents at harvest are shown in Figure 3.

Moisture content at harvest is the dominant environmental factor affecting head rice yield. The morphological factors affecting head rice are uniformity among kernels for shape, size and volume. The percent of hull and kernel shape are the principal factors affecting total rice and volume. Physiological factors that apparently improve head rice are rapid grain filling rate and high kernel density (volume/weight). Density appears to be related to the duration and rate of grain filling as well as the volume.

Uniformity among kernels on a single panicle is a difficult problem to study. In the present study, differences among kernels on different parts of the panicle were measured. Based on these differences, it was found that variation in maximum kernel weights and grain densities were more detrimental to head rice yields than the other variations studied. Variations in maximum kernel weights and density were induced by variations in rate of grain filling and shape.

Based on present knowledge, breeding for improved head rice yield should give major attention to selecting for uniformity among kernels in size, shape, volume and density on the panicle. Since kernels within a single panicle differ in their time of maturity, selection should be for plants whose panicles flower and reach maturity as simultaneously as possible.

On the single kernel basis, head rice yields are improved by rapid grain filling, large volume, high density and small percentage of hull. Varieties ranked from less to more uniform kernels were L-202, M-101, M-201, S-201, M-302 and M7. Ranking for percentage of head rice was essentially the same. Knowledge of various characteristics contributing to improved head rice yields has advanced considerably with the past year's research and could lead to varieties with improved head rice yield.

Figure 3. Head rice yields of the long-grain variety L-202 are compared with the short-grain variety S-201 and the medium-grain variety M-201 when harvested at various moisture contents.

Product Development - Objectives

• Continue studies and promotional activities with stabilized rice bran, rice oil, and new rice products.

The rice utilization and product development project is conducted by the Western Regional Research Center, U.S. Department of Agriculture at Albany, California. The center, with partial support from the Rice Research Board, has developed and promoted the use of stabilized rice bran as a source of edible oil and has developed other new products to increase the use of rice. New products have included rice flours, rice sugar syrup and blended nutritional supplements for children.

The Western Regional Research Center is working with several rice marketing groups that have started producing stabilized rice bran since the procedure was invented by the center several years ago. Currently, Farmers Rice Cooperative, Comet Rice, and PIRMI are producing stabilized bran. The center is monitoring the oil content and stability of the final products. It also negotiated a change in Japanese entry specifications so that stabilized rice bran from California could enter Japanese markets. Entry specifications also were negotiated for exporting stabilized rice bran to Korea.

Promotional activities are continuing for new rice products developed through previous research. One result is the anticipated significant increase in the use of stabilized rice bran in foods. Rat feeding experiments have been conducted with a California firm that produces rice syrups, from which a high-protein byproduct is a potential infant food.