Soils: February 2006 Other Soils Articles

Summer annual forages are sometimes used to meet forage production needs in the Noble Foundation service area. Unfortunately, there are no current university yield tests of these in Oklahoma or within our service area in Texas. This project was undertaken to identify adapted species and varieties of summer annual forages and quantify their yields.

Small plot variety trials were conducted during the summers of 2001 through 2004 in Ardmore, Okla. We evaluated one sudan, three pearl millets, 12 sorghum sudans and seven forage sorghums. Planting and harvesting were done mechanically. Sub-samples were taken at each harvest and analyzed for crude protein (CP) and total digestible nutrients (TDN).

Sudan produced an average of 8,154 pounds per acre dry matter (DM) per year. Pearl millet varieties produced an average of 7,423 lbs/ac DM per year. Sorghum sudan varieties produced an average of 7,217 lbs/ac DM with a range from 9,723 to 5,024. Forage sorghum varieties produced an average of 5,230 lbs/ac DM with a range from 6,697 to 4,067.

The four highest-yielding entries in the test were sorghum sudans (Table 1). However, the highest-yielding species and varieties do not always give the most economical production. This is due to differences in seed and fertilizer rates and costs. Over the four years of our study, pearl millet was as productive as the average sorghum sudan, but required 50 pounds per acre less nitrogen (N) and was more efficient with the N it received (Table 2). There were no significant yield differences between the pearl millet entries we tested. CP and TDN were similar for all entries, but highly variable within and across years.

We also included brown midrib and photoperiod-sensitive varieties. Brown midrib varieties did not show improved TDN or CP. Photoperiod-sensitive sorghum and sorghum sudan did not out-yield traditional varieties.

Be sure to evaluate your own production costs and needs when selecting a variety for your operation.

A companion study was also done to evaluate summer annuals for wildlife food plots. We evaluated four cowpeas, Korean and striate lespedeza, two forage soybeans, one mungbean, hyacinthbean and lablab. It would be unfair to compare these to each other because they are widely differing species and fill different niches. Table 3 gives an indication of average annual production. Keep in mind that CP and TDN values are based on mechanically harvested whole-plant samples, and what wildlife would selectively consume would likely be higher in value.

Cowpeas had the longest vegetative period and re-grew well after harvest. They produce high-quality forage with no significant differences between varieties. Korean lespedeza appeared to reseed itself, which may be an added benefit. The soybeans and mungbean did not seem to be as drought tolerant as the cowpeas, and, after they went reproductive, quality decreased rapidly. The benefit of the mungbean is that they are very fast producers – 60 days or less.

Sticking with the theme of evaluating: In my October 2005 article, I evaluated some tools for cutting cedar trees. The manufacturer of the ATV-mounted cutter was concerned we may not have used the unit properly. On Dec. 14, 2005, we met in Ardmore for a contest matching him and his machine against me with a chainsaw. We agreed to call it a draw. One thing we learned is that the cutter's blades need to be touching or within thousandths of an inch of touching. Another thing we learned is the ground clearance of the machine is probably more important than the size of the machine, and newer machines tend to stand higher. We were also hitting the trees too fast and too hard. With the blades properly adjusted, much less force is needed to cut the tree, and, therefore, the impact is much less. Thanks to Steve Scott of ATV-X for coming and spending time with us.

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