Take a look at variable-rate planting

Question: Why all the buzz about variable-rate planting?

Andrew Hofner: With farms becoming more reliant on GPS technology, the opportunities to more precisely apply crop inputs are expanding. What started out as only variable-rate lime and fertilizer application by a commercial applicator has now evolved to the farmer having the capabilities to adjust nitrogen product rates and planting populations on the fly or from variable-rate prescription files.

Variable-rate planting can maximize a field’s yield potential while managing the
in-field variability during a tough growing season. By planting the correct rate, issues with moisture, lodging, disease and weeds are minimized through ideal inter-plant spacing and competition.

Question: Why should I use it?

Hofner: Even on the most uniform fields, there are places where drainage or soil fertility does not allow that area to match the productivity of the rest of the field. Being able to adjust planting rates allows you to manage those areas as well as take advantage of the more productive areas that should be pushed to the limit.

Question: Will this practice cut seed costs?

Hofner: As seed costs have risen, farmers want to get the most from their seed purchase. Variable-rate planting shouldn’t be looked at as a way to decrease seed costs. It’s a way to maximize potential by applying the population that matches the capabilities of the specific acre on which the seed is planted.

Question: What determines the population?

Hofner: Think of what the crop needs to grow and make bushels. Mitigating moisture stress and equalizing inter-plant competition are keys to calculating what population an area will support. For corn, lighter soils that have low moisture-holding capacity are more likely to have stalk lodging issues and smaller ear size. Darker soils with higher organic matter content have a high capacity to hold moisture in late-summer drought situations but have high weed pressure as well.

In lighter soils, a grower is better served by lowering the corn planting rate to 28,000 to 30,000 seeds per acre to reduce the risk of stalk lodging due to moisture stress while still maintaining yield. On darker soils, higher planting populations (35,000 to 37,000 seeds per acre) maximize yields and keep weed pressure to a minimum.

Question: How about soybeans?

Hofner: For soybeans, lighter soils tend to have low seed germination rates, while darker soils have more yield potential but are more prone to disease and lodging. For those reasons, think about soybean population rates in reverse of corn planting rates.

On the lighter soils, the soybean planting population should be increased (180,000 to 200,000 seeds per acre) to allow a respectable stand to grow and compensate for droughty conditions. In the darker, more productive soils, the population can be decreased to 120,000 to 140,000 seeds per acre because of better emergence and higher bloom/pod retention due to less drought stress. Lower soybean populations also reduce stand density, thereby decreasing disease potential and lodging.

Question: What directs the planter?

Hofner: The planter uses a variable-rate planting prescription in the monitor to adjust rates based on multiple layers of data that document the field’s productivity. Correct planting population is determined by soil types and yield potential of a field. Mapping those parameters accurately is critical for a good planting prescription.

Question: What data is used and how?

Hofner: At Integrated Ag Services, we build a “productivity index” for each field. It is comprised of several data layers, including a Veris EC layer that we collected; a soil organic matter layer we have generated from one of the following: a Veris organic matter sensor, or a 1-acre or half-acre grid soil sampling; a normalized yield data layer collected by the grower spanning three to four years; and a slope layer created from RTK elevation data collected out of the grower’s harvest monitor. If you don’t have all of these data sets, a combination of two or more will provide a very detailed picture of the field’s yield potential.

Once the available data sets are combined into the productivity index, planting rates are assigned to match productivity.

Question: What if planting runs late?

Hofner: Hybrid and variety selection and planting date affect final variable-rate planting recommendations. Most planting monitors allow the operator to adjust the prescription at planting time to account for last-minute changes.

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This article published in the October, 2011 edition of OHIO FARMER.

All rights reserved. Copyright Farm Progress Cos. 2011.