Peanut farmers in North Carolina now have an advisory to help them assess the risk of moving from conventional to reduced-tillage systems. Interest in reduced-tillage in peanuts has been on the increase in North Carolina because of changes in the peanut program and the incidence of tomato spotted wilt virus.
The advisory should help farmers determine on a field-by-field basis whether the risk is worth the benefits.
David Jordan, North Carolina State peanut agronomist, and one of the principal authors of the advisory index, says research suggests that reduced-tillage systems can work for peanuts in North Carolina.
Authors include Rick Brandenburg, Extension entomologist; Barbara Shew, Extension pathologist; and George Naderman, former Extension soil scientist; and Steve Barnes, former superintendent of the Peanut Belt Research Station; and Clyde Bogle, superintendent, Upper Coastal Plain Research Station, N.C. Department of Agriculture and Consumer Services.
“Growers adopting reduced-tillage systems may need to spend more time in overall management of peanuts, particularly early in the season,” Jordan says. “This especially applies to weed management.”
That means moving away from soil-incorporated to pre-emergence and post-emergence herbicides and preparing strip-tilled beds in the fall.
Savings in tillage costs are often offset by increased herbicide costs in reduced-tillage, Jordan says.
In many cases, yield is lower in reduced-tillage than in conventional-tillage systems. That's why it's important to assess the risk to peanut yield before using reduced-tillage in a particular field, Jordan says.
Drawing on the advisory model of the TSWV Risk Index, the “Index for Transitioning from Conventional to Reduced-Tillage Peanut Production in North Carolina” assigns points to determine low risk, moderate risk and high risk of reducing tillage in peanuts.
A low risk is a total number of 30 points or less; a moderate risk, 35 points to 65 points; and a high risk, 70 or more points.
The index considers market type, irrigation, soil series, tillage intensity, small grain cover and history of TSWV. The Index does not incorporate the economic impact of each component.
When transitioning to reduced-tillage, a low-risk scenario would involve planting Georgia Green under irrigation on a Conetone series soil, strip-tilled in beds with a winter cover crop and a history of TSWV. In fact, this scenario is ideal because it totals zero. It would be highly unlikely to reduce all negative risk to reduced-tillage in peanuts, Jordan says.
A real world example of a 25-point, low risk would include planting Gregory without irrigation on a Norfolk sandy loam, strip-tilled into with a winter cover crop and a history of TSWV.
An example of high risk of lowering yield under reduced-tillage: NC 12 C planted with no irrigation on Roanoke soil, no-tilled flat, with no winter cover crop and no history of TSWV. This scenario goes to the opposite end of the risk range at 110 points.
An example of moderate risk, at 45 points, would involve planting NC-V 11 with no irrigation on Norfolk soils, strip-tilled flat with a winter cover crop and a history of TSWV.
Another moderate-risk example: Planting Gregory without irrigation on Craven soils, strip-tilled in beds with a winter cover crop and a history of TSWV. This scenario would total 55 points.
Because Virginia-type peanuts have larger pods than runner-type peanuts, they have a greater risk of reducing yield because they are more difficult to remove from the ground. “Greater resistance from soil can cause a higher percentage of pods to strip away from the vines,” Jordan says. Under the index, Virginia-type peanuts are assigned a risk of 5 points, while runner peanuts because of their size don't pose a risk.
Irrigation or timely rainfall can help create soil conditions that minimize pod loss during harvest. Irrigation serves as insurance if soil conditions are less than favorable at harvest. No irrigation is assigned a 10-point risk level in the index.
Pod loss on finer-textured soils such as Roanoke and Craven series is often greater than on coarser-textured soils such as Conetone and Wanda regardless of the tillage system. In the Index, Roanoke and Craven pose the greatest risk to pod loss at 40 points. Goldsboro and Lynchburg soils are assigned 20 points while Norfolk soil is assigned 10 points. Conetone and Wanda soils pose zero risk to pod loss when converting to reduced-tillage.
How peanuts respond to reduced-tillage systems is invariably correlated with the degree of tillage. Digging peanuts can be difficult when peanuts are planted on flat ground in reduced-tillage systems. Strip-tillage into flat ground is a better alternative, but not as good as strip-tillage into pre-formed beds. Peanuts grown on strip-tilled, pre-formed beds often have yields approaching those of conventional-tillage. In the Index, no-tillage into flat ground, at 40 points, poses the greatest risk to decreased yields to reduced-tillage. Strip-tillage into flat ground has a risk of 20 points in the Index. Strip-tillage into stale seedbeds has zero risk.
A small grain cover crop conserves soil moisture and reduced wind and water erosion. It also contributes to soil tilth and can minimize winter weed populations. A cover crop can also can make the choice of a burndown herbicide easier. Under the Index, the absence of a cover crop adds 5 points to the risk of reducing yields.
It's been documented that reduced-tillage means less TSWV and fewer thrips. “Generally speaking, there is less risk of yields being lower in reduced-tillage systems if the virus has occurred in the past because reduced-tillage systems suppress TSWV,” Jordan says. “The increased yield as a result of TSWV suppression may offset at least a portion of yield loss that might have occurred due to other agronomic or pest management practices in reduced-tillage systems.”
As in other advisories, Jordan is quick to point out that there's little way to reduce all the risk. “The Advisory Index is a way to help producers determine if converting to reduced-tillage may be a risky move,” Jordan says.