As I write this May 3, the outdoor temperature is 72º. Spring is trying to come to life, without much success. Maple trees are pollinating enough to cause lots of coughing and sneezing, an unwelcome milestone arriving about a month later than normal. Shade trees are just starting to blossom, something which normally takes place around the start of spring. Most years, by the first week of May, pasture is advanced to the point where it can be grazed, so that there’s abundant browsing before the vegetation is munched down to that critical four-inch level. That’s my first “four.” The general recommendation for when to start grazing the most advanced paddock is when mostly legume stands are 10 to 12 inches tall, or when mostly grass stands are six to eight inches tall. For folks with hilly topography, lower altitude paddocks tend to mature a little bit faster (air temperature tends to drop, on average, about 1º F for every 300 feet in increased altitude).
It’s not mandatory that swards be grazed down to four inches. Think of the four inches as a warning bell or alarm, not a goal. It’s been shown that grazing shorter than that lengthens the recovery period, delaying the time at which animals can be returned to the paddock in question. Thus, grazing too short reduces the potential amount of forage that can be mouth-harvested on that paddock during that particular growing season. One successful grazing practice involves ruminants eating the top third of standing vegetation and then being moved on to the next paddock. In most situations, this avoids hitting that four-inch minimum, plus pre-empts later-grazed paddocks from getting too far ahead of the livestock. Four inches is also the minimum height to cut perennials, summer annuals (like sorghum, sudangrass, their hybrids and millets) plus winter forages and any crop where a second cutting is hoped for.
With pasture coming on slower than normal this year, it’s wise to keep feeding cattle in the barn until the mostly legume fields hit that 10- to 12-inch height target, or mostly grass fields hit that six- to eight-inch target. It’s a good business move for a grazier who’s running low on mechanically-harvested forage to buy some hay crop (usually baleage) from a neighbor in order to delay a start-up date for this year’s pasture programs. Be sure to check out the hay ads in Country Folks. Over-grazing paddocks stuns them badly, prolonging recovery periods, lowering total digestible dry matter produced per acre for the whole season. For back-up to this idea, I tap into the wisdom of pasture aficionado Greg Brann: “A bale fed in early spring… and waiting till the grass is ready… will be worth four bales of summer grass production later, not to mention the fertility transfer back to the soil.” There’s another four – looks like a 300% return on investment.
Research on my part revealed that Brann, owner and operator of Big Spring Farm, emphasizes overall diversity on his farm located on the Kentucky/Tennessee border. His efforts to increase farm diversity not only apply to forages, but also to livestock. Brann rotationally grazes cattle, sheep and goats in one large herd. A large variety of forages including both cool-season and warm-season species are strategically seeded for grazing and land management. Brann received a bachelor’s in plant and soil science from the University of Tennessee, with special emphasis on animal science and landscape design. He runs a livestock management consulting service and often lectures at livestock conferences.
I’ll quote him again: “The starting grazing height will vary some according to the species, but generally you want a minimum of eight inches of growth for most species and rarely do you want to graze it down any lower than four inches. Maintaining adequate live plant residual is critical in keeping the plant growing and thriving.” These fours just keep on coming. Brann defines over-grazing as “grazing below where most carbohydrates are stored. This results in high utilization, but production can be reduced by as much as two-thirds.”
The last “four” comes early in the book “Omnivore’s Dilemma” by Michael Pollan. Pollan writes that where most plants during photosynthesis create compounds that have three-carbon-atom modules, corn – along with certain other species – creates compounds that have four-carbon modules. They’re in the carbon-4 (C-4) class, which wasn’t identified until about a half-century ago. What’s special about the C-4 trait is that it provides a critical economy, particularly in areas of scarce water and high temperatures. In order to gather carbon atoms from air, plants must open their stomata, the microscopic orifices on the leaves, through which plants take in and exhaust gases. Every time a stoma opens to admit carbon dioxide, water molecules can escape.
Quoting Pollan: “It’s as though every time you opened your mouth to eat, you lost a quantity of blood. Ideally, you would open your mouth as seldom as possible, ingesting as much food as you could with every bite. This is essentially what a C-4 plant does. By recruiting extra atoms of carbon, during each instance of photosynthesis, the corn plant is able to limit its loss of water, and ‘fix’ – that is, take from the atmosphere and link in a useful molecule – and thus significantly more carbon than other plants.” As Pollan continues singing corn’s praises in “Omnivore’s Dilemma,” he fails to mention some of the other crops that belong to the C-4 class – sorghum, sudangrass, millet and sugarcane. This book was published in 2006. At that time it was known that Johnsongrass was a C-4, and a weed, but not a terribly bothersome weed. Also, turns out that members of the pigweed family are C-4s; sadly, that includes Palmer’s amaranth, but in 2006, that was just an occasional ink spot in the farm press. “Better” things were yet to come.