A computer analysis for head rice yield of 5,000 farm samples by Dr. Shu Geng provided information on the effects of variety, temperature and  moisture content at harvest time.

Rice kernel dimensions were measured because they are believed to influence such factors as mechanical stress and milling quality. The two short grain varieties S6 and 5-201 did not differ statistically from each other in grain length nor did they differ among areas where grown. S-201 was slightly greater than S6 in grain width. Statistically significant differences in grain length among medium grain varieties did occur. The hulled grain lengths of M9 were greater than M101, Earlirose or M7. Lengths of these three varieties were greater than M301. Calrose and M-301 were equal. Length did not differ for production areas. Width of hulled medium grained varieties varied among varieties and area of production. It has not yet been possible to determine if kernel dimensions affect total milling yield and head yield.

Studies were made on the rate and duration of grain filling of California varieties grown in three different locations in the Sacramento Valley. Results indicate that genetic differences exist as well as differences for location and cultural practices, particularly levels of nitrogen fertilization. Experiments conducted in growth chambers demonstrated that high daytime temperatures (86°F) during grain ripening increased grain filling rate and decreased grain filling duration of the variety M-101. Grain development was retarded at low daytime temperatures (68°F), and the grain filling period was prolonged.

The effects of variety, moisture content at harvest, production area, and several management practices on total milling yield, head yield, and chalkiness are still being evaluated. Preliminary observations indicate that varietal quality is significantly changed by moisture content at harvest, time of harvest, and management practices.

The effects of variety, moisture content at harvest, production area, and several management practices on total milling yield, head yield, and chalkiness are still being evaluated. Preliminary observations indicate that varietal quality is significantly changed by moisture content at harvest, time of harvest, and management practices.

Foliar fertilization of rice does not appear to significantly improve rice yields where adequate preflood soil applications are made. These foliar spray treatments were made at the panicle initiation, early booting, and 50 percent heading stages.

Iron toxicity can be a problem in flooded acidic rice soils where large amounts of organic matter are incorporated, particularly on the red terrace soils. In nutrient culture experiments, increased iron composition is accompanied by exclusion of potassium. Consequently, the observed yield depression may be a combination of iron toxicity and potassium deficiency.

Slow release nitrogen fertilizers have not shown a significant yield advantage over commercially available ammonium-nitrogen sources when they are incorporated 4 to 6 inches deep in the soil prior to flooding.