Cultivar and Environmental Influences on Head Rice-87
 
 

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Project Leader and Principal UC Investigators

Shu Geng, Dept. of agronomy, UC Davis

 

The study of interrelationships among drainage timing, cultivar type and nitrogen level and their effect on panicle development, kernel characteristics and head rice yields is increasing understanding of how these factors influence rice yield and milling quality.

The upper part of the panicle usually has the fastest grain filling, and its grains are heavier than those in the middle and lower parts of the panicle. Drainage treatments have little effect on duration or rate of grain filling. However, high nitrogen rates prolong grain filling by two to seven days.

Drainage time appears to be important to rice milling quality, with late drainage generally being more favorable to head rice yield. Data also suggest that a high level of nitrogen must be accompanied by late drainage to maximize head rice yield and that a high level of nitrogen combined with early drainage could be detrimental to head rice yield.

There are significant differences in grain filling rates among the three varieties studied. The grain filling rate of L-202 is faster than for M-201 and S-201. However, the maximum panicle weight for L-202 is less than for the other two varieties. S-201, which tends to fill its grains more slowly and over a longer period, produces heavier seeds than the other varieties.

A milling quality model has been developed to explain the causeand-effect relationships among grain characteristics and head rice yields. Basically, the structural variables (shape, volume, percent hull, etc.) affect the physiological processes (grain filling duration and rate) and, therefore, the weight and density of the rice kernel. The structural variables and the weight and density of the kernel directly determine the potential head rice percentages.

California Studies Challenge Degree-Day Concept

The concept that the developmental stages of a plant can be expressed as a function of degree days, or heat units, has been well accepted by plant scientists and has been documented for many crops. However, previous studies in California indicate that a simple degree-day approach may not be adequate for predicting developmental stages of a rice plant and that the number of days after planting may be a better predictor.

Preliminary analysis based on data collected from 24 rice fields in Butte County supports the hypothesis that the best predictor for California rice plant development is days-after-planting rather than degree-day summations.

Computer Software Selects Harvesting Moisture

A computer program called RICEECON has been developed to perform certain economic analyses and produce an accounting report of a farm's net gain or loss. It has the following uses: 1) estimation of head rice percentage at a fixed harvesting moisture level; 2) determination of the optimal harvesting moisture for a given variety; and 3) the economic consequences of harvesting at optimal grain moisture.

 

Head Rice Yield Influences Studied

Next to field yields, milling quality is the most important factor affecting what price growers get for their crops. While California has always yielded well, milling quality has been comparatively low, and especially so, in the last few years.

UC Davis agronomist Shu Geng examines factors affecting head rice development.

"It's become more noticeable since the industry has begun to switch from late maturing to early maturing cultivars," noted project leader and UC Davis agronomist Shu Geng. "There've been many suggestions why - weather, engineering, drying and milling. Those are all crucial to head rice, but we're looking at it from another point of view the cultivar."

At both the CCRRF facility in Biggs and UC Davis, Geng's research team set out with the specific objective of investigating the effects of cultivar type, time of drainage and rate of nitrogen application on the growth and development of panicles, kernel uniformity and head rice yields.

"We found that cultivar type is very important," Geng said. "Now we're looking in more detail into what are the traits we can measure so we can select cultivars with high milling quality. But milling quality is complex. There isn't just one most important factor; there are many."

The researchers are also investigating whether the traditional degree-day concept is the best method of gauging rice development and have created a computer program called RICEECON that will help growers determine the best time to harvest.

 

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