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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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.

EPTC IO percent granules, Trifluralin 10 percent granules and Poast were evaluated for southern sandbur (cenchrus echinatus) control. Trifluralin resulted in variable control ranging from 90 percent down to 55 percent. EPTC produced good but sometimes varied control when applied in February, prior to the germination of the weeds, and repeated in April, June and July. Poast was effective postemergence only when applied to small seedlings. It was ineffective when applied to established sandbur.

Alfalfa irrigation is often withheld as a water conservation measure in Arizona. The objective of this research was to test the hypothesis that alfalfa yield and stand can be permanently damaged by withholding irrigation water. Irrigation was terminated during the summer (July through October) or winter (November through February) on a Superstition sand in Yuma. Summer irrigation termination reduced plant density from 4 to 1.5 plants per square foot and reduced hay yield from 0.76 to 0.27 tons per acre per cutting after irrigation was resumed. Winter irrigation termination had no residual effect on yield or plant density. Termination of alfalfa irrigation can permanently damage stands and reduce yield on sandy soil.

Alfalfa irrigation is often withheld as a water conservation measure in Arizona. The objective of this research was to test the hypothesis that alfalfa can be permanently damaged by withholding irrigation water. Irrigation was terminated during the summer (July or August through September) or summer through winter (July or August through mid -March) on a Casa Grande sandy loam at Maricopa. Irrigation termination at Maricopa was not detrimental to stand although hay yields were depressed from 1.47 to 1.28 tons per acre following the second cycle of summer irrigation termination and from 1.57 to 1.23 tons per acre per cutting following summer through winter irrigation termination. Alfalfa water use was reduced by irrigation termination even after irrigation was resumed. Total nonstructural carbohydrates in the roots were never less than the control during irrigation termination but decreased relative to normally irrigated alfalfa when irrigation resumed.