Improved yields have been a major objective since the beginning of the research program.

UC research under this program was directed partly toward the development of analytical tools to estimate fertilizer needs and to develop better methods of correcting deficiencies in rice plant nutrition. Two of these methods - soil analysis and rice tissue analysis - are now widely used by California agricultural laboratories, field men, and farm advisors to estimate the fertilizer requirements of each rice crop. Soil analysis is now extensively used in estimating phosphorus, potassium, and zinc fertilizer requirements, while rice tissue analysis is valuable in estimating nitrogen, phosphorus, and potassium contents of plants.

Research showed that zinc, not iron, was needed to correct adverse conditions in alkali rice soils.

The "alkali" problem, caused by a zinc deficiency, appears in rice as chlorosis in seedling plants and partial loss of stand. It was shown that relatively low rates of zinc fertilizer could be used at a third or less the cost of commonly used zinc-contaminated commercial iron sources, such as ferric sulfate and iron oxide. The savings to California rice growers since 1969 in reduced costs to control "alkali disease" are estimated at more than $2 million (see figure 3).

Figure 3. The research finding that it was zinc, not iron, that was needed to correct the "alkali" problem in rice has saved California rice growers over $2 million for control measures since 1969. Plots to your right received zinc sulfate; those to your left received none. Extension Agronomist D. Marlin Brandon is looking along the dividing line. (UC Cooperative Extension photo)

The productivity of old rice soils can be increased by placing phosphorus fertilizer near the seed of rice rotation crops. Yield increases of more than 1,000 pounds per acre have been recorded in field experiments with rotation crops such as barley, wheat, safflower, and grain sorghum (see figure 4).

It has been shown in commercial rice production that flooding of soil for rice culture greatly increases the capacity of the soil to adsorb phosphorus once the soil has been drained. The adsorbed phosphorus is unavailable to crops which are planted shortly after rice, resulting in severe phosphorus deficiencies in such crops. The increase in value of crops after rice as a result of restoring the phosphorus is estimated at more than $14 million above fertilizer costs in the past five years.

Better management of nitrogen fertilizer can produce better yields in new rice varieties.

Laboratory and field research has indicated that new tall varieties, such as M5 and S6, require about the same rates of nitrogen as the older commercial tall varieties. However, the new short-stature varieties, Calrose 76, M7, and M9, are more responsive to nitrogen fertilizer and usually require higher nitrogen rates than the tall varieties for maximum yield. Experimental results indicate that the critical level of tissue nitrogen in short-stature varieties is similar to that of the tall varieties. Nitrogen fertilizer is utilized more efficiently by the short-stature varieties because of their superior genetic makeup, and it appears that these rices will increase grain yields about 10% and decrease straw yields by a similar amount when fertilized with optimum rates of nitrogen.

Figure 4. Research found the answer to poor rotational crop growth following rice. Banded phosphorus gives early vigorous growth of safflower (left) on old rice land, compared with poor growth where phosphorus is not provided (right). Both plots received the same amount of nitrogen fertilizer. The findings of this research have been exploited in wide commercial use, returning Sacramento Valley rice farmers an extra $14 million over fertilizer costs during the past 5 years. (UC Cooperative Extension photo)

Future research objectives of rice soil and plant nutrition.

Research on rice soil and plant nutrition, by its very nature, is continuing and evolutionary. Some projects within this area may be concluded in 2 to 5 years as acquired data is converted to commercial practice. Other objectives will take longer. Following, in brief, are the research objectives for 1977 and beyond:

1. To determine the plant nutrient requirements and fertilization practices in potential new California rice varieties which will be conducive to the full expression of yield potential before and shortly after their release.
2. Study the behavior of all California rice varieties in different climatic regimes to determine adaptive, nutritional, and management requirements.
3. Develop and correlate improved diagnostic soil and plant analysis tests suitable for evaluating the nutrient status of all California rice varieties. Develop plant tissue tests which can be used in the field by rice growers and commercial field men.
4. Study the effects of soil submergence on the physical, chemical, and biological properties of soils as they affect rice production.
5. To identify and ameliorate the factors in flooded soils which limit the growth, development, yield, and quality of rice.

Obtaining nitrogen from the air in the style of legumes has been explored for riceland use.

A water fern (Azolla) acts in concert with a blue-green alga to fix nitrogen from the air. Study has shown that it will grow well in rice fields, suppressing weeds if started in the fields at the right time, dying before rice emergence, and releasing nitrogen as it decays. It produces about half the nitrogen the rice crop needs, according to determinations of nitrogen in the entire system (soil, water, crop, and weeds). The study covered Azolla as a companion crop for rice, as a green manure, and as a combination of the two. Integrating such a system into California agriculture would require the development of new crop-management techniques. The Board's support of this exploratory study has brought about major support from other sources for its continuation.