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Water 2012: Green manure and cover crops: a water saving method

Posted: Wednesday, Dec 5th, 2012

A Valley green manure field this summer. Courier file photo by Lauren Krizansky

This is the 49th in a weekly series celebrating Colorado Water 2012.



VALLEY — Irregular rains have some Valley farmers and ranchers trying old tricks to conserve water and protect agriculture.

Planting green manure/cover crops (gm/cc) to sustain the Earth might be as old as irrigation itself. It is similar to placing an umbrella over the soil, which sounds like something that would keep the water out, but it has the reverse effect. The umbrella is protection from water stressing erosion and weed growth, and it makes the soil stronger to combat disease, insects and other environmental challenges through organic recycling and nutrient transfers. In specific regard to water conservation, gm/cc offer a triple bonus, according to an Oklahoma State University (OSU) study. A living cover crop traps surface water, and when it is killed and left on the field, it increases water infiltration, lessens erosion and reduces evaporation. These water saving crops can include legumes, grasses and root crops like radishes and turnips, a common mix now found in Valley fields.

Barley and potato fields in the central Valley are regularly incorporating gm/cc and the farmers are witnessing change. Rockey Farms, Center, has reduced water use to an average of nine inches per acre annually compared to the conventional 15 to 22 inches used for a two-year potato/grain crop rotation. Rob Jones, a certified organic farmer in Mosca, has tried a number of cover crop combinations to benefit his potato production and increase water efficiency. He averages two cover crops a year using combinations of peas, oats, rye, clover, radishes, vetch and buckwheat, and has not used more than 12 inches of water to keep the rotation alive.

During the 2012 Southern Rocky Mountain Agricultural Conference and Trade Fair earlier this year, The Natural Resources Conservation Service (NRCS) reported that gm/cc use less than 17 inches of water a year, particularly when sordan grass is incorporated into the crop rotation. It proved to lower erosion rates and water use in studies.

There are a variety of ways to incorporate the practice into traditional crop rotation. In the Valley, summer green manure crops are grown in time with cash crops and are therefore irrigated to reach desired stages of growth. Some Valley producers are planting cover crops in the fall and their growth is subject to timing and rainfall once irrigation is shut off for the season. Although they are at the mercy of Mother Nature, non-irrigated cover crops that emerge before winter sets in are providing valuable biomass that assists water retention, prevents soil erosion and contributes to a healthy soil structure regardless of their size. Hipshot Farms, Hooper, has managed to produce fields of cover crops to use as grazing land and bailed forage in the spring, and claims that alongside its ecological benefits, it is a viable commercial product.

During the growing season, gm/cc’s retain soil moisture when crop transpiration rates are greatest and rainfall is seasonally at its lowest, according to one university study. Residues left over from killed gm/cc increase water infiltration and reduce water evaporation from the soil surface in no-till planting, allowing conservation tillage systems to provide moisture that would otherwise be lost through evaporation. Covering the soil with gm/cc also reduces crusting and subsequent surface water runoff.

The more ecological deterioration that has taken place, especially as far as soil quality and rainfall regularity are concerned, results in a more limited selection of gm/cc species that grow well, stated one study. Nevertheless, when the gm/cc’s have improved the soil somewhat, farmers can often graduate to less hardy varieties that produce more additional benefits like keeping fertilizer-based nitrates out of the Valley’s aquifer and poisoning the essential element. It could prevent a future situation similar to California’s Central Valley battle with contaminated aquifer water that is a result of more than half a century in which chemical fertilizers, pesticides and other substances that have seeped into the groundwater and eventually into the tap, according to a recent New York Times report.

Such natural soil health building, water retention and recycling practices are recorded throughout agriculture’s history. In the United States, E.H. Faulkner, a one-time extension agent and a lifetime farmer, brought attention to using the Earth’s own production to maintain living soils with minimum inputs, including water. He published The Ploughman’s Folly 69 years ago, and its claims came in a time when agriculture was uniting with technology, increasing yields and promising food security for many more than ever before. Faulkner’s theories, which included turning the green manure back into the fields, had Time magazine calling the debate against conventional agriculture the “hottest farming argument since the tractor challenged the horse” in 1944.

Although the farmer watched the grasses and foliage of nearby woodlands flourish when his crops fell victim to drought and the weeds thrive when seeds grew no taller than a sprout, according to Faulkner, he did not think to understand the vitality of a decomposing leaf and undisturbed beds. He failed to study the situation until the land squandered, “leaving no valuable inherited lore of the soil,” but only man-made stories handed down with warnings of drought and shortage.

With the Valley’s water resources becoming scarcer everyday, and water laws and irrigation practices bending to meet the needs to man and its dependence on nature, opportunities for farmers and ranchers to incorporate gm/cc into their operations are growing. In the Rio Grande Sub District One, producers have the option to access funding for gm/cc rotations instead of leaving fields fallow to meet the new irrigation requirements. According to the OSU study, water storage efficiencies in traditional fallow systems are usually around 20 percent, while water storage efficiency in alternative systems is near 40 percent, but seldom exceeds this amount, meaning 60 percent of the precipitation received during fallow is lost to evaporation. Although following significantly reduces irrigated water use, it also leaves the ground vulnerable to erosion and pioneer plants, and without any food to retain or improve soil nutrients. These outcomes could result in land degradation that would need much rehabilitation before reintroducing commercial production and tempt producers to speed up the process through chemical-based resources, restarting the conventional cycle and recreating the problems water resources and modern agriculture face today.

For more information on Water 2012, please visit www.rgwcei.org or www.water2012.org. The next Rio Grande Basin Round table meeting will be held on Tuesday, Dec 11th from 2 p.m. to 5 p.m. at the Ramada Inn in Alamosa.

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