Nutritive & Environmental
Factors Affecting High
Yield Potential-80

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Project Leader and Principal UC Investigators

D.S. Mikklesen, Dept. of Agronomy and Range Science, UC Davis

F.E. Broadbent, Dept. of Soils and Plant Nutrition, UC Davis


Coated rice seed (left) and uncoated seed. Dr. D.S. Mikkelsen from UCD continued coating studies in 1980. Coating rice seed with calcium peroxide and fungicides may make it possible to eliminate the preplant seed soak operation. It may also lead to the use of preflood application of herbicides to control weeds.

The following are highlights of the findings from this research:
  • Calcium peroxide as a seed coating is a satisfactory oxygen extender, which when used at a 30 percent seed weight, successfully provides emergence of rice seed through 2.5 centimeters of soil and 10 centimeters of water.
  • Degradation of calcium peroxide coated on rice seed is affected by soil pH, soil organic matter levels, microbial activity in the soil and heavy metal catalysts. Use of lime with peroxide retards degradation.
  • In a statewide evaluation of the phosphorus status of California rice soils, about 18 percent of the area sampled showed need for phosphorus fertilization.
  • Soil test comparisons and calibrations from preliminary greenhouse-laboratory experiments indicate that the sodium bicarbonate-phosphorus extraction test (dry soil basis) correlates well (0.8937) with plant phosphorus responses. A critical value of 6 parts per million extractable phosphorus is recommended for soil test evaluations.
  • The partial efficiency of phosphorus applied to rice is highest when fertilizer phosphate is applied at time of planting. Seedling growth stimulation is better from broadcast phosphate, but grain yields were not affected by method of application. Unincorporated broadcast phosphorus will also stimulate weed seedlings, particularly barnyardgrass.
  • Preliminary critical values for evaluating the sulfur status of California rice varieties suggest that 0.15 percent sulfur is the critical value for plants in the mid-tillering stage.
  • In deficiency situations, phosphate can be top-dressed on rice until the panicle stage with some yield benefit, but response declines with delayed applications up to about 60 days after planting.
  • Draining rice fields may cause significant losses of fertilizer nitrogen through nitrification-denitrification if soils dry to less than complete saturation.
  • The nitrification inhibitor, nitrapyrin, used on urea does not appear to improve nitrogen use efficiency by rice when compared with untreated urea fertilizer.


Area rice specialist Jack Williams looks on as Cooperative Extension agronomist Dr. James Hill discusses the Cooperative Extension seed coating field experiment on the Demeter Company farm. To the left is an extensive variety test. The coating test proved that even coated seed can be covered too deeply. Farmers and Cooperative Extension play a vital role in field testing Rice Experiment Station and University f California research results.



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