Manure and alfalfa: Testing new liquid application equipment with traffic-tolerant varieties

By: Melissa Wilson, Extension manure management specialist, and Josh Gamble, USDA-ARS research scientist

Key Points:

• Growing perennials, like alfalfa, can have water quality benefits while still producing a crop for cattle feed
• Using manure during the alfalfa rotation is often avoided, leaving a smaller land-base for manure to be applied
• New liquid manure application equipment plus the use of traffic-tolerant alfalfa varieties may reduce some of the negative aspects of manure application on a living crop like alfalfa

What we did:

We have two main goals in this ongoing study:

1. Evaluate a traffic tolerant variety of alfalfa for manure application
2. Determine if the use of dairy manure, fertilizer, or a combination of both throughout the 3-year alfalfa growth cycle could be used to maximize growth and quality

We established two different varieties of Roundup Ready alfalfa in the spring of 2021 at the University of Minnesota’s Rosemount Research and Outreach Center: Pioneer 54VR10-RR (high yielding, FD-4) and Ameristand 455TQ-RR (traffic tolerant, FD-4). Prior to establishment, we either applied phosphorus (P) and potassium (K) sulfate fertilizer according to soil test needs or injected dairy manure slurry at about 3,000 gallons per acre to supply full P needs for the first year (about 27 pounds of P2O5 per acre). Each set of treatments was replicated in large strips four times. We harvested the alfalfa twice in the first year and sent samples for forage quality analysis. We also evaluated crown health of plants in each plot, took soil samples to evaluate nutrient uptake and carbon cycling, and monitored nitrate leaching at a depth of four feet below the alfalfa crop.

What did we find?

The following results are from the first year of a three-year study. We experienced a drought in the 2021 growing season at Rosemount, MN (we had 11 fewer inches of rain than usual), so yields were lower than expected. The conventional alfalfa (Pioneer 54VR10-RR) yielded 1.8 tons of dry matter per acre, which was higher than the 1.5 tons of dry matter per acre for the traffic-tolerant variety (Ameristand 455TQ-RR). Across both varieties, manure applied pre-establishment increased yield by about 8% compared to the plots where only P and K sulfate fertilizer were applied. Samples for forage quality have not been analyzed yet.

As for plant health, plants were dug by hand in early November prior to a killing frost and scored on a scale of 1 to 4. A rating of “1” meant the plant was healthy (it had a robust crown and large root) and “4” meant the plant looked questionable for survival (there were few crown buds and the plant had a small root). The percent of healthy plants scoring a 1 or 2 was calculated for each treatment. Generally, the traffic-tolerant variety of alfalfa had a higher percentage of healthy plants (53%) than the conventional variety (46%). For the traffic-tolerant variety, pre-establishment manure increased the percentage of healthy plants (57%) compared to fertilizer only (47%). The manure treatment had no effect on the percentage of healthy plants for the conventional variety. This was a bit surprising and will be interesting to see if manure application plays a role in stand longevity and yield in upcoming years of the study.

What’s next?

This past fall, we further divided the research strips into smaller sections to evaluate nutrient management practices. After the second cutting in late August, we either applied dairy manure or left some plots for spring-applied P and K sulfate fertilizer. The intent with the manure application was to supply enough P and K for the second-year alfalfa crop. The dairy manure was applied in several different ways to see which methods worked the best for stand longevity. These included: broadcast, banded on the surface (15 inches apart), or shallow injection (about 4 inches deep and 30 inches apart). About 6,000 gallons per acre were applied with each method to supply about 76 pounds of P2O5 per acre. We’ll continue to monitor the alfalfa during the 2023 and 2024 growing seasons (applying nutrients the same way as this past fall in fall 2023). We’ll also continue monitoring soil nutrient and carbon cycling and nitrate leaching. Keep your eyes out for future updates!

Acknowledgments:

This work is supported by the USDA-ARS through cooperative research agreement number 58-5062-1-008 and the National Alfalfa and Forage Alliance.

A version of this blog post first appeared in the Dairy Star.

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