fall planted crops fertilizer rainfall

Lingering impact of summer rains could be problem with fall-planted crops

• Record rainfall make future planning critical. • Soil sampling is vital to replacing lost soil nutrients. • Fall and winter weed control is important for future crops

Many fall-planted crops in the Upper Southeast have been set back from 3-6 weeks by late harvest of spring-planted crops, caused by excessive rainfall throughout much of the growing season.

As growers begin to finish up late harvest of soybeans, cotton and other crops, there is a need to plan for late-planted fall crops.

Soil testing will be more critical in many areas of the Southeast than in recent history, again due to the excessive rainfall, which in many cases depleted soils of many vital crop nutrients.

South Carolina Extension Agent Charles Davis says some good advice for growers in the Low Country of his state will be to soil test, soil test and soil test again. “We’ve never had rain at this level in my lifetime, so there will be many variable in terms of crop nutrients that we simply can’t predict without accurate soil testing,” he says

Fertilizers are significant variable costs in production and it pays to assess crop nutrients in fields. Soil testing is a relatively inexpensive but powerful management tool that determines nutrient levels in fields. With knowledge gained from soil tests, you can make more informed crop input decisions to minimize risk and maximize profitability.

DuPont Pioneer recently released a number of timely fall reminders for growers, including the need for soil testing. They say, “Sampling three to six months prior to the next crop allows enough time for any pH or nutrient adjustments. For many crops, the optimum time to take a soil sample is in late fall during post-harvest.”

Applying fall nitrogen for spring crops may not be the best option, especially for growers in the Southeast who persevered through one of the wettest growing seasons on record. Placing nitrogen closer to planting date may be a better option, but only after extensive soil sampling to determine the amount of nutrients left in the soil after the historic rains.

Driven by logistics

“Fall applications are largely driven by logistics and an effort to spread out the workload. If you have the equipment and manpower, it’s better to wait to apply nitrogen in the spring,” says Neal Hoss, DuPont Pioneer technical services manager. “If you don’t have the capacity for spring applications, target fields with the least amount of risk and use nitrogen inhibitors to minimize the potential loss of your nitrogen investment,” Wilson advises.

Several soil sampling techniques are available, and this year may be a good one to take a closer look at grid and zone sampling and investing in GPS technology to allow for variable rate application of N, P and K.

P and K fertilizers applied in the fall are more stable, offering less risk than fall-applied N. If you’re trying to reduce your spring workload, P and K fertilizer applications can easily be done in the fall, when weather and soil conditions are generally not as wet, which diminishes concerns about compaction.
In the upper end of the Southeast, freezing weather, perhaps some isolated ice and snow are predicted for the first full week in November.   

If weather or a late harvest delays application, avoid applying P and K on frozen or snow-covered fields due to a high risk of loss with surface runoff. In such cases, application prior to planting in the spring is just as effective, as long as soil test levels are above the very low range.

Flooding, combined with the natural movement of weed seeds is a real good reason to take a close look at fall weed control. North Carolina State Weed Scientist Wes Everman says anything growers can do to reduce the seed bank in the fall will reduce weed pressure in the spring, especially for no-till or minimum till operations.

Palmer pigweed in particular can be a big problem, if small, stunted seeds are allowed to persist after early fall harvest of spring crops. These weeds can become low growing for a while, but can still grow and produce seed, which can cause major problems in the spring, Everman says.

Conversely, he adds, don’t depend too much on winter herbicide applications to negate the need for spring burndown.

“Keeping weed populations as low as possible in the fall and winter will help, but Palmer pigweed, and other weed species also will need early attention in the spring when growers begin getting soil ready for spring 2014 crops,” the North Carolina State Specialist says.

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