Summer Annual Variety Trials

In the summer of 2008, the Noble Foundation conducted replicated small plot (5'x 20') variety trials of forage sorghums (FS), sorghum sudans (SS), sudan grasses (SU) and pearl millets (PM). We tested many of the same varieties that we tested in the past¹. The difference was this year we moved the location to our Dupy Farm near Gene Autry, Okla. The Dupy site has a very productive loamy bottomland soil. In the previous trial, we evaluated pounds-per-acre dry matter (DM) yields of these grasses on a claypan prairie soil. The Dupy site also gave us the opportunity to have rain-fed and irrigated plots within ¼ mile of each other on the same soil type. Plots were fertilized as in the past with 60 pounds per acre actual N at the beginning of the season and topdressed with 40 pounds per acre actual N for each subsequent cutting.

A more detailed report of all the results will be available as a fact sheet later, but I would like to discuss some key points from the 2008 trial at this time.

1. Four of the five highest yielding varieties from 2001-2004 were still in the highest yielding group in 2008. These varieties are Fastgrass 5-SS, Sweet Sunny Sue-SS, Summergrazer III-SS and Piper-SU. (Seed of the fifth variety was no longer available.)
2. All of the statistically highest yielding rain-fed varieties were also in the statistically highest yielding group when irrigated. These varieties are Fastgrass 5-SS, Summergrazer III-SS, 2S-SS, Sweet Sunny Sue-SS, Piper-SU, Gotcha Plus-SS, Trudan 8-SU and 8493-SS. However, not all of the varieties in the highest yielding group when irrigated were in the highest yielding group under rain-fed conditions. These varieties are 2 Way-FS, 1990-FS, Sordan Headless-SS and Sugar Graze Ultra PS-SS. I would feel comfortable choosing a variety for irrigated production using only rain-fed data, but not vice versa.
3. It appears that irrigation may be necessary to take full advantage of improved quality from the brown midrib (BMR) trait. Under rain-fed conditions in 2008 as well as in our past trials, crude protein (CP), acid detergent fiber (ADF) and total digestible nutrients (TDN) of BMR varieties were not significantly better than conventional varieties. However, in this single year of data and with irrigation, FS 6810 BMR-FS and Surpass BMR-SS had significantly better quality than other SS and SU varieties.
4. There were no significant differences among pearl millet varieties for CP, ADF or TDN under rain-fed conditions and no significant differences among pearl millet varieties for DM, ADF or TDN under irrigated conditions. In the past, under rain-fed conditions, there were no significant differences for any traits among any of the pearl millet varieties we tested.
5. Pearl millet produces higher quality forage than sorghums, sudans and their crosses, but yields less total tonnage. Averages for 2008 are listed in Table 1.
6. There were no significant differences among forage sorghum varieties tested in 2008 under rain-fed conditions.

Yield and quality are inversely proportional under rain-fed and irrigated conditions. Higher yielding forage types tend to have lower protein and nutrients, and more fiber, while lower yielding forage types tend to have higher protein and nutrients, and less fiber. Similar results were seen in previous tests. However, it is important to note that irrigation improves the quality within a forage type. This is due to more vegetative/leafy growth with irrigation when compared to rain-fed conditions.

¹See "Noble Foundation Evaluates...," February 2006 Ag News and Views