by Keith Baldwin, CFSA’s Farm Services Coordinator
Down here in the Piedmont they say there ain’t much coming in from the field in August. But it’s a month where growers can make an investment in their soil resources. Provided there’s some moisture in the soil, now is the perfect time to get a summer cover crop in the ground.
Cover crops provide multiple benefits. Chief among them is enhanced soil quality, which is defined by improvements in soil fertility, physical properties and microbiological ecology. Cover crops capture and recycle nutrient “leftovers” from previous crops, suppress weeds, biologically fix nitrogen, increase soil organic matter content and moisture retention and add diversity to cropping systems.
You need as little as a 30 day “window” to make something happen with buckwheat, and it’s a great crop. Quick to bloom, it brings predators and parasites to feed and to prey on insect pests in adjacent fields. It covers quickly, and is easy to manage after it’s finished. Every farm should have buckwheat cover somewhere on the farm. The one downside of buckwheat is that it doesn’t give you very much above ground biomass, so soil organic matter benefits are on the short side.
But there are other summer cover crops to consider as well. Warm season legumes fix sizable amounts of atmospheric nitrogen (N) in as little as 45 to 60 days. A summer workhorse is cowpea, preferably a “forage type” cowpea such as ‘Iron Clay.’ Cowpea is better than a forage soybean if deer are a problem, because the deer won’t totally destroy them. And, they make a quick comeback after pruning. Either species will provide 80 units of N per acre and upwards of three tons of dry matter, so you get N and organic matter benefits. Organic cowpea seed is available, but organic “forage” soybean seed can be hard to find (lakevieworganicgrain.com has an organic soybean they claim can be grown for forage. ’4010’ forage pea is available at lakevieworganicgrain.com, Welterseedandhoney.com and Albert Lea seed). Research at the Center for Environmental Farming Systems (CEFS) showed that both cowpea and soybean will do equally well, whether planted June 1, July 1 or August 1.
There is a great summer legume that is finally being priced right for the market: sunn hemp (Crotalaria juncea). As usual, to get the best price, you need to buy a 50 bag. But if you do, you can get the seed for under $2.00/pound. There are several seed dealers that will provide documentation that the seed was grown and is available without any seed treatments or genomic interference. But organic seed is not available. Petcher Seeds in AL has sunn hemp as does Hancock (cheaper, $89/50 lbs). Petcher says he provides a letter to organic growers stipulating that the seed is not treated with prohibited substances. He “says” certifiers in CA allow the use of his seed (actually from S. Africa) on certified farms.
Sunn hemp is very quick to produce biomass with over 3% N, closing in on 100 units of N per acre in 45 days and four tons of dry matter in 60. You probably don’t want to let it grow longer than 60 days, as the stems gets quite fibrous and hard to manage after that. But it can make these numbers with a planting date as late as August 1st. Auburn University has been doing breeding work and has come up with a couple of cultivars that will produce seed in the Deep South (‘AU Bolden’ and ‘AU Durbin’).
If you’re after biomass and soil organic matter benefits, and the N benefit is secondary, the two grasses to consider are hybrid sorghum sudangrass and pearl millet. If you’re going to graze it, definitely go with pearl millet as the former can be toxic (prussic acid) to livestock. Both of these are quick and much better than the shorter statured millets such as German or Japanese foxtail. They will give you dry matter tonnage. The shorter millets mature more quickly and are much better in bio-cultures with cowpea or soybean. Both are easily killed by mowing close to the ground.
Sorghum sudangrass is available as certified organic at HighMowingSeeds.com, blueriverorgseed.com, Albert Lea Seed (allseed.com) and lakevieworganicgrain.com. Pearl millet seed is not available anywhere as organic (as far as I can tell). Untreated seed is available at welterseedandhoney.com, Hancockseed.com and lakevieworganicgrain.com. Welter has non-treated German foxtail, Japanese and pearl millet.
For cultural information on planting these crops, see http://www.ces.ncsu.edu/hil/hil-37.html.