Crop Comments: Selecting the right C-4 summer annual

As I’m writing this column early on June 30, the weather forecast for the Utica area spotlighted this headline: “Dangerous heat to hit parts of U.S. ahead of July 4” – with worst hit areas being the Northeast. According to David Robinson, climatologist at Rutgers University, “A heat dome (hitting the Northeast) keeps out clouds, precipitation and breezes, so there’s a lot of sunshine and no rain or wind to cool things off.” This problem will still be playing out when this issue of our paper reaches subscribers’ mailboxes. A major factor intensifying drought in already water-deficient areas is the loss of soil organic matter (OM). With every 1% loss of OM, the soil’s water reservoir benefit drops by about 16,000 gallons/acre. Thus, it’s particularly important that wherever moisture is very limited, soils have sufficient OM to retain what little rainfall growers receive. The increasingly common corn/soy non-rotation (absent cover crops/winter forages) slowly but surely dissipates soil OM. These two crops lack the fibrous root systems so necessary for building up carbon reserves, and with them that critical water reservoir trait. Regarding moisture management, let’s tap into the wisdom of University of Texas agronomists. They tell us that when rainfall is deficient, a given quantity of precipitation supports twice as much forage dry matter growth from sorghum and/or sudangrass as from whole plant corn forage. From North Dakota State University (a state with an average rainfall of 17 inches), we learn that millets are even more efficient than these other two species at converting water to forage dry matter. With the idea that millets need even less water than sorghum, I recommend planting this crop on soils with less than 4% OM. Plant sorghums and sudangrasses (or their hybrids) when OMs are in the 4% - 6% range (hopefully the latter are available in “gene-6” varieties). With sod OMs exceeding 5%, the moisture reserve situation should be adequate to support short season corn silage hybrids. Growers do well to plant such corn varieties on fields where first-cut hay crops have just been harvested. Further support for millets comes from Purdue University agronomists, who say that millets can be grown in a wide range of environmental conditions because they’re already well-adapted to hot, dry regions. They were some of the earliest prehistoric crops to be cultivated as a staple food in China, India and Siberia as well as Europe and parts of Africa. All millets possess the C-4 photosynthetic trait. (In the Northeast, the common millets are Japanese and pearl.) Corn, sorghum, sudangrass (their hybrids), millets and sugarcane are classified as C-4 crops. During photosynthesis, most plants create compounds by using three-carbon modules. But the six crops just listed perform their carbon-structuring function by using four-carbon modules. The C-4 trait is advantageous, particularly in regions where too much heat combines with too little water. Here’s why: in order for a plant to gather carbon atoms from air, it opens up its stoma (microscopic openings on its leaves). C-4 group members use their stoma to limit water loss as well as retain acquired carbon. They do so more efficiently than C-3s. Here’s how these crops rank in terms of moisture retention “skills”: millets, sorghums, sudangrasses, (their hybrids), sugarcane, then corn. Plant scientists generally believe that corn is at the end of the list because its genus (Zea) developed in higher altitude (thus more humid) conditions in central Mexico. They lacked the genetic pressure to perfect this aspect of the C-4 trait. In research drawn from India (the country growing the most millet), scientists determined that millets can be grown on soil less than six inches deep. They don’t require rich soils to survive. They fit well into India’s abundant drylands. Indian agronomists stress that millet relies on very little synthetic fertilizer. Farmers growing millet there get by quite well with barnyard manures coming from milking water buffalo. According to some of those agronomists, “In recent times, household-produced bio-fertilisers (sic) significantly reduce the huge burden of fertilizer subsidy borne by the government. Grown under traditional methods, no millet attracts any pest. Therefore, their (millets’) need for pesticides is close to nil. Thus they are a great boon to the agricultural environment.” Northeast sustainable farmers growing millet have a lot in common with their counterparts in ancient farming cultures. I’ve discussed oppressive drought conditions, but when the precipitation pendulum swings the other way, millets fare quite well with moisture surpluses. Millets, particularly Japanese, can be grown in wetlands, depending on the region. It doesn’t grow well on sandy soils but grows well on flooded soils, and even standing water, as long as part of the plant remains above water. The crop’s major shortcoming is its intolerance to frost. Immediately following a killing frost, millets (and the other C-4 crops) should be mowed within two days, then chopped or baled rapidly, so as to minimize field loss from shattering of overly dried forage. Japanese millet has coarse leaves and grows up to five feet tall, depending on moisture availability and fertility. The seed head is four to eight inches long and dark purple in color, with no awns. Seed may be drilled (no deeper than one inch) or broadcast. The recommended drilled seed rate is 20 lbs./acre. Bump that up to 25 - 30 lbs./acre when broadcast. When millet is headed out, harvest it as forage, because it’s already done creating roughage dry matter. In the Northeast, there’s little likelihood of it drying down enough to combine successfully. At most locations in our region, millet can be planted up to July 15 and should be ready to harvest by Sept. 21. Another plus for millet, should you decide to harvest its aftermath regrowth, is that there’s no prussic acid to threaten cattle. However, growers planting corn next year on the same piece won’t have that carried-over natural poison to fight off rootworms. Millets are also slightly more tolerant of lower pHs than the other C-4 crops. by Paris Reidhead