Brad Brown, Soil Scientist, University of Idaho
Roger Gibson, Scientific Aide

Brad Brown, Parma Research and Extension Center,
29603 U of I Lane, Parma, Idaho 83660
bradb@uidaho.edu 

Accomplishments
Table 1
Table 2
Projections
Acknowledgements

Accomplishments
Table 1
Table 2
Projections
Acknowledgements

Accomplishments
Table 1
Table 2
Projections
Acknowledgements

Accomplishments
Table 1
Table 2
Projections
Acknowledgements

An established alfalfa seed trial was conducted on a Greenleaf silt loam at the Parma Research and Extension Center during the 1999 and 2000 seasons. The trial involved mobile (B) and nonmobile micronutrients (Zn, Cu, Mn, Fe) either (1) injected 9 inches deep with knives into the furrow bottom, (2) broadcast and shallowly incorporated (triple K) April 14-15, 1999 or (3) foliar applied at late bud in each season. Only the foliar treatment was re-applied in the 2000 season. Treatments were arranged in a randomized complete block with five replications. Individual plots were 8 rows wide (22" row spacing) and 50 feet long. The injected and broadcast treatments in 1999 were applied at rates of 5 lb/A of Zn and B and 2 lb/A of Cu, Mn, and Fe. Foliar treatments were applied June 14, 1999 and June 13, 2000 at the late bud stage using the same rates except for B which was applied at only 0.5 lb/A.

Soil samples were collected April 13, 1999 from the 0-12" and 12-24" depths for background residual fertility. Initial soil test values for the 0-12" depth were 7.4 pH, 0.4 mmhos/cm salt, 3.5% lime, 1.06% OM, 17.2 ppm P, 157 ppm K, 0.24 ppm B, 1.3 ppm Zn, 1.0 ppm Cu, 6.2 ppm Mn, and 21 ppm Fe. Of these analyses only soil test B appeared to be limiting according to published critical soil test B levels (0.5 ppm).

Above ground plant biomass at late bud was measured June 16, 1999 from 12 ft² and B, Zn, Cu, Mn, and Fe contents determined. Whole plant biomass for injected Zn-Cu-Mn-Fe was greater than for the control, injected or broadcast B treatments (Table 2). But none of the micronutrient concentrations or their uptake in whole plants were affected by injection or broadcast applications.

In the 2000 season, alfalfa buds and the top 6" of the upper stem were collected at late bud and their micronutrient concentrations determined. Bud tissue B and Fe concentrations tended to be lower than in upper stem tissues, possibly reflecting the poor translocation of these nutrients from other plant tissues (Table 1). In contrast, bud tissue Zn was higher than in the upper stem tissue. Micronutrient concentrations were not appreciably affected by the application treatments.

The alfalfa was sprayed with defoliant August 16, 1999 and August 28, 2000. Significant wind and hail damage with rain occurred August 12, fifteen days prior to the 1999 harvest (August 27), with total precipitation for the day measuring 0.3". Appreciable volunteer alfalfa evident in late fall confirmed significant seed loss from this storm. In the 2000 season 0.67" of rain occurred on September 1 followed by 0.12" on September 4. Seed was harvested September 7. The field run seed was further threshed in an enclosed thresher with rubber paddles to separate seed from intact curls. The seed was cleaned on a Clipper and the brown, light, nonviable and heavier, amber colored viable seed separated using an air cylinder.

Seed yield in 1999 averaged only 132 lb/A due to hail injury and was not significantly affected by treatments (Table 2). The 2000 season seed yields averaged 453 lb/A across all treatments, appreciably better than in 1999, but still lower than yields reported by many producers. However, seed yield was affected by treatments in 2000. Seed yield increased with B applied in 2000 regardless of the application method, with yield increasing from 40 to 53%. Among B methods of application, the foliar treatment appeared to be the most effective although methods did not differ statistically.

Seed yield in 2000 increased also with the mix of Zn-Mn-Cu-Fe with yield increasing from 22 to 55%. The broadcast application appeared to be superior to deep injection or foliar applications. It could not be determined whether the yield increase was due to any particular micronutrient or the mix as a whole. The variability of yields each year from this small plot trial was high in this study and points out the difficulty of conducting small scale research with this crop.

Seed Mn was the only nutrient increased by its application in 1999. Results from the 2000 harvest were not available.

In summary, whole plant alfalfa micronutrient content at late bud in 1999 and bud and uppermost raceme micronutrient concentrations at late bud in 2000 were largely unaffected by the micronutrient applications, regardless of application method. Tissue tests for micronutrients failed to reflect increased micronutrient availability to the plant from the applications despite increases in biomass production at late bud in 1999 from the Zn-Cu-Mn-Fe mix and seed yield increases in 2000 from both B and the mix. Despite DTPA soil test values for Zn, Mn, Cu, and Fe that were above published critical levels initially, alfalfa seed increased in yield with their application, especially when broadcast uniformly and shallowly incorporated. In contrast, the seed yield increase from B was greatest from the foliar application.

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This concludes a two year study on mobile and non-mobile micronutrient placement and need for alfalfa seed production. Deep injection provided no advantage over broadcast micronutrient applications. The results suggest that late bud tissue testing using whole plant, bud or upper stem tissue have little value in predicting the need for supplemental micronutrient applications. The results demonstrate that both B under low soil test conditions, and a Zn, Mn, Cu, Fe mixture, despite moderate soil test levels, can under some conditions appreciably increase seed yield. It is not clear how widely these results may apply to commercial fields in the area. Additional studies are not planned for the coming year.

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ACKNOWLEDGEMENTS:

This research was conducted with the encouragement and assistance of Dr. Karen Strickler who provided the necessary background and oversight for the timeliness of field operations, pollinator management, and pest control. Dr. Takugi Noma and Crystal Fortney are also acknowledged for their assistance with pollinator management and insect monitoring provided for this field study.