In a natural vegetative system, soil, regardless of quality or texture, naturally releases nitrogen in the summer and plants suck it up. When corn, wheat or any row crop is planted, the crops suck up the nitrogen, but then are harvested, leaving the soil bare until the next crop is planted.
Ideally, grain crop farmers would grow crops in soils in which nitrogen and carbon combine to release nitrogen and for that nitrogen to be available to the crop. That type scenario doesn't occur over-night. If steps being recommended by NCRS agronomists across the country are closely followed, results, primarily in reduced N requirements should be evident in 8-10 years.
Traditional row crop production is not a natural system, notes Chris Lawrence, NRCS agronomist in Richmond, Va., The way to grow crops in a more natural system is to imitate nature, the Virginia agronomist says.
The first step he says is to make a commitment to long-term, no-till farming and to building nitrogen in the soil. A key to that commitment it always have something growing in the field. In a naturally occurring system, there is always something growing to keep nitrogen production in balance. Over time, he says, keeping something growing in the field all the time will have environmental, agronomic and economic benefits.
It is critical in this long-term investment to have a legume in the rotation. Lawrence points out the obvious, that N has to come from somewhere and legumes are nitrogen-fixing plants.
“Asking grain farmers to make this kind of commitment is difficult,” the Virginia agronomist admits. “It does add an extra cost, and it doesn't provide much return on investment for the first few years,” he says. Long-term, he explains, the benefits are well worth the investment. “We have growers who have been building N by using some of these practices for over 10 years, and some of these farmers have grown 95 bushels of wheat per acre with little or no fertilizer,” he explains.
The ultimate mimicking of nature is to grow a lot of residue for the sole purpose of putting it back down into the soil. This is critical to organic, no-till farming and may be a way to speed up the nitrogen building capability of grain farm soils. The key, Lawrence contends is to grow a high volume, high biomass cover crop. In some cases rolling and crimping may be a way to fully utilize the cover crop.
The cover crop's main function is to reproduce. Once it fulfills that function, it is ready to die. If a cover crop is caught at the right stage of growth, when it is ready to die, it can be rolled and crimped, which doesn't kill it, but prevents it from growing upright. This allows farmers to plant directly into the cover crop and to get maximum benefit from its nitrogen potential.
If cover crops are rolled and crimped too late, it has already produced viable seeds, which creates unwanted competition for the following crop. If the cover crop is rolled and crimped too early, the full benefit of the crop residue won't be available to the soil, plus the roller will miss some of the plants, leaving them to grow and produce seed.
Rolling and crimping opens the door to no-till organic farming. If the system is used correctly, it eliminates the need for a burn down herbicide to kill the cover crop. And, if a cash crop is established there will be a definite mulch benefit for weed control. With good systems and plants, plowing can be eliminated, making for a true organic system, Lawrence contends.
The drums on most roller/crimpers are designed to be filled with water to add enough weight to avoid bounces, which could create skips in a rolled field. Another design feature is to sweep the roller bars back at less than a 90 degree angle to the roller drum. Otherwise, plants can be ripped from the ground, leaving bare soil. In organic farming, there are no herbicides, and bare ground produces weeds.
It is critical to plant behind the roller/crimper in the same direction. Otherwise, the planter will tend to push the cover crop back up. The planter used by Lawrence's research team was attached and matched to the roller/crimper.
“The key is to have high biomass, and to get high biomass from any cover crop, it is critical to time rolling and crimping properly,” Lawrence stresses. Conventional growers, with late planted soybeans, planting into a cover crop may save a burn down herbicide and may eliminate the need for weed control, the Virginia agronomist stresses.
“Spoon feeding crops nitrogen with high tech equipment is great, and we need to be as efficient as we can. However, we are always going to have some nitrogen coming out the bottom.
“From an agronomist's perspective, we can utilize the lost nitrogen and prevent it from escaping into the atmosphere by using plants and plant systems. These systems can produce enough income for the grower and have perennial nitrogen uptake — but it takes time and commitment,” Lawrence explains.
In some cases in which grain crop land is rented, it may take a long-term commitment from both the farmer and the landowner, Lawrence contends. Most grain farms operate on large acreages with low profit margins, so it is particularly difficult for the farmers who would benefit the most from a long-term nitrogen saving system to invest in the system, the Virginia agronomist explains.
“It all comes back to a quality soil building system, Lawrence contends. In a natural system the soil is only disturbed by roots and microorganisms that open up a soil and give it a natural structure. Tillage also opens up the soil, but in an unnatural way, according to the Virginia agronomist.
In long-term no-tillage systems residue from year after year of crops becomes a part of the soil. Keeping cover crops on the field year-round not only prevents leaching of nitrogen, but takes carbon that would be released into the atmosphere as carbon dioxide, and instead, this carbon is going back into the soil.
When synthetic liquid nitrogen is put on crops, no carbon is being put into the soil. By building organic matter with cover crops, soils with high organic matter hold nitrogen, which releases slowly over time. As farmers get further and further along in continuous no-till farming and nitrogen building the benefits of reduced fertilizer get larger and larger.
“A few years ago, I would never have thought like an organic agronomist, but I agree with many of the concepts of organic farming. In our area of eastern Virginia, long-term no-till farmers are using less nitrogen fertilizer — that is documented.”
Mark Alley, a professor of agronomy at Virginia Tech University is conducting a series of tests in eastern Virginia to determine more precisely how much nitrogen is available from long-term no-till systems. Because continuous no-till farming has caught on in eastern Virginia, it is easier for farmers there to make additional steps in soil nitrogen building, Lawrence points out
The key is commitment to long-term soil quality. Otherwise rolling and crimping, nor many of the advanced features of soil nitrogen building will pay off, Lawrence concludes.
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