Strip-till considerations in Oklahoma
click image to zoom Though strip tillage can be successful without GPS based guidance, this is one instance where this technology can be beneficial. GPS guidance systems allow the operator to minimize driving error and return to the previous paths created by strip tillage. The increased popularity of GPS guidance has allowed farmers to apply fertilizer and till strips in the fall and return to those same strips in the spring to plant even when the strips are not visible. Farmers are typically using real-time kinematic (RTK) auto guidance systems for strip tillage applications (Figure 3). These systems are the most expensive and offer pass-to-pass accuracies of about 1 inch. The least expensive guidance systems with single frequency and WAAS differential corrections have pass-to-pass accuracies of 8 to 10 inches and will likely not provide sufficient accuracy and precision for strip tillage applications. However, dual frequency GPS receivers with pass-to-pass accuracies of about 4 inches may provide sufficient accuracy for strip tillage. The operator may need to use the ‘shift track’ feature periodically to make sure the planter stays near the center of the strip. Researchers at Purdue University evaluated GPS auto guidance on a simulated 1,800 acre corn-soybean farm in the Corn Belt. Their analysis and assumptions found DGPS auto guidance was more profitable than light bar guidance and RTK auto guidance when expanding acreage beyond 1,800 acres or controlling traffic on the 1,800 acre farm.
click image to zoom The underlying assumption to driving accuracy in strip tillage is that yield will decrease as you plant further from center of the strip. Research in Oklahoma has found some potential benefits of precision planting. Figure 4 shows a graph of irrigated corn yield versus driving error for strip tillage plots at the OPREC in Goodwell. This data shows that there is no significant yield decrease until you plant 4.5 inches from the center of the strip. Since the strips were about 8 to 9 inches wide, there was no penalty until you planted outside the strip. This data shows yield loss of 6 bu/ac for every inch of driving error away from the edge of the strip.
When the planter moves off the strip, it is in a no-till environment and if it is not adjusted correctly for no-till, stands may not be as good. The data from Goodwell supports this observation. Final stands for the plots with driving errors greater than 4.5 inches were lower than those with errors less than 4.5 inches. Though this one year of data from the panhandle certainly supports a need for at least 4.5 inch driving accuracy, research in Stillwater found no yield benefit to improved driving accuracy.
Strip-till in Oklahoma can fit into many cropping systems throughout the state. The benefits of strip-till include increasing the soil temperature in the seedbed, maintaining residue cover between the rows to conserve soil moisture, and providing options for fertility management. Soil moisture conditions at the time of strip-tillage and planting will likely determine if a producer will see a benefit from strip-tilling in a no-till system. Strip-till is an excellent way of converting cropping systems from conventional till to no-till systems because strip-till provides benefits of both systems.
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