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Ten alfalfa varieties, ranging from very non - dormant to moderately dormant cultivars, have been grown and yields compared over a five year period. The yields decreased dramatically this last year, to 5.3 tons per acre down from 10 tons per acre during the second season. Differences in production between the top and bottom varieties was 4.75 tons per acre. Figuring hay values at $100 per ton, this difference would mean a loss of $19,000 over the 5 year period on a 40 acre field.

Yields are given for 20 varieties of alfalfa grown at the Safford Agricultural Center. Yields were down slightly from 1990. Mecca retained its number one position with a yield of 9.22 tons per acre and yielded nearly 4.4 tons per acre more than Cuf 101, over the four years of the trial.

A test was conducted to evaluate the effect that renovating a weak alfalfa stand had upon yields in one field in the Yuma Valley. Results indicated that yields were not significantly different in the renovated vs. the not renovated plots. Under the conditions present in this test, there appeared to be no yield advantage to renovation during the first year.

A survey was conducted to evaluate the soil phosphorus levels in a cross section of established alfalfa fields in Yuma County The levels of extractable phosphorus (P) varied from 3 to 43 ppm P. All of the soils testing in the very low (below 5 ppm P) and low categories (5 -10 ppm P) were located in the Wellton-Mohawk Valley and on the Yuma Mesa. Annual soil testing in the fall should be used to identify fields which would be expected to be responsive to P fertilizer applications. Soil testing could also help identify fields less like& to respond to P additions (P values > 15 ppm). Eighty percent of the fields tested from the Yuma and North Gila Valleys were in the high and very high ranges, 16-25 ppm and > 25 ppm P respectively. These high values may reflect residual P from applications of phosphorus fertilizers to vegetable and cotton crops grown in rotation with the current alfalfa crops. Fall soil testing in these areas could help identify nonresponsive fields in order to avoid unneeded P applications.

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No description available.

A test was conducted to evaluate the effect of irrigation termination during the summer (July through October) and winter (October through February) upon alfalfa yield and stand Termination during the summer harmed the stand and seriously reduced yields. Termination during the winter resulted in minor yield reduction and no stand damage. The benefits of suboptimal irrigation are site specific and dependent upon many factors. This test demonstrated that the winter should not be overlooked as a time to conserve water on alfalfa production.

Substantial plant loss is a commonly accepted phenomenon in commercial alfalfa production. Frequently less than 2% of the seeds originally sown are present in productive mature stands. Optimum yields may not be achieved if the small proportion of plants that survive do not represent the most productive individuals in the original population. We began a study in 1989 to describe the relationships between survival (persistence) and productivity in alfalfa. Sixty 5 yr-old plants were dug from a field of CUF -101 in Pinal Co. (= "Persistent population "). Field performance of progenies of these plants were compared with those of 60 greenhouse -grown CUF-101 plants (= "Random population ") in a 2-yr study in Tucson. In the second year of production spring and fall forage yield and average rate of stem elongation were significantly lower in the Persistent population than in the Random population. These data suggest that plants that are able to persist for the average life of a stand may represent a subset of the original sown population which exhibit more conservative growth patterns. This indicates that simultaneous selection for traits associated with productivity and persistence may be necessary in alfalfa breeding.

Yields are given for 22 varieties of alfalfa grown at the Safford Agricultural Center. Yields were 2 to 3 tons lighter than those in 1989. Mecca retained its number one position with a yield of 8.86 tons per acre and a total of five varieties had yields above 8 tons per acre. It is of interest to note that three of the top five varieties were developed by the Plant Genetics group in California.