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 ConceptThe 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 MoistureA 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.
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