The farmers will be participating in a variable-rate application study on 4,000 acres that could reduce their inputs by at least $63 per acre while bumping yield by 60 pounds.

Late last summer, the producers acquired aerial images of several of their cotton fields. The images, shot with an airplane-mounted camera in green, red and near infrared, were loaded into a JSCC computer and geo-referenced.

Then a software function called normalized differential vegetative index (NDVI) classed each field into three productivity zones – low, medium and high. These zones are highly correlated to eventual yield.

JSCC then developed a “computerized mission plan” for VR applications in the fields. This coming season, when it’s time to apply inputs, the growers will simply load a chip in the controller on a VR sprayer to variably apply lime, pre-plant fertilizer, seedling rate, in-furrow fungicide, in-furrow insecticide, Pix, top-dress nitrogen and in-season insecticides. Inputs will be varied according to which zone the equipment is passing through.

The VR application itself is easy and the cost of modifying equipment for VR relatively inexpensive – about $18,000 for a 1,000-acre operation.

In 2002, JSCC conducted a similar VR experiment on 1,000-acres in west Tennessee. It indicated that growers could pay for the technology in one year, even adding the cost of gathering and analyzing the data.

According to Tim Sharp, JSCC professor, three west Tennessee farms were used for the 2002 study. In 2001, an airplane shot imagery of the fields late in the season and JSCC computers generated the NDVI images of the field.

Fields across the three farms were paired – one of each pair was managed using conventional application techniques and the other with VR application.

Data was collected in the zones at various times. Information included stand count, first position retention, plant height, total nodes, identification of first fruiting branch, elongation at the fourth internode, yield maps, total final plant maps and soil grid sample data.

For the study, the variable-rate fertilizer application was grid-sample driven and applied on all fields, even those conventionally managed – to remove fertility as a variable in the test results.

Seeds were planted at a rate of two per foot in low zones, three in medium zones and four in high zones. Most of the VR technology used on the sprayer rig was also used on a planter.

In-furrow fungicides and Temik were applied in the low zones at 50 percent of what was applied in the high zones, and at 75 percent in the medium zones.

One application of Bidrin was made over the study at 60 percent, 80 percent and 100 percent in low, medium and high zones. Pix was applied at zero, zero and 100 percent, respectively.

Plant mapping indicated the most significant improvement in the retention of first position bolls, nodes and total bolls in the low zones with variable-rate application versus conventional, according to Sharp.

Overall, yield in variable-rate fields was 63 pounds higher than in conventional fields, “plus we spent about $60 less in reduced input costs from variable-rate application. So we’re looking at $100 less per acre in the variable-rate fields.”

Sharp noted that there was no difference in yield between conventionally managed and variable-rate managed fields on first pick. However, the second pick was where growers picked up the extra yield or 33 pounds more in the high zones, 73 pounds more in the low zones and 83 pounds more in the medium zones.

Sharp also observed some other characteristics of the productivity zones. For example, medium zones can act like high zones if they’re managed correctly and like low zones if they’re not. In many cases, where a grower has unexpectedly high yields, it’s often the medium zone that has done the work.

In addition, in irrigated cotton, where farmers often push the low and medium zones for more cotton, they can inadvertently “blow up” their high zones – create boll rot or allow excessive growth. In that situation, it may actually be better to reduce inputs such as nitrogen in the high zone, and/or increase Pix. VR can be used to pinpoint those areas.

For more information and photos of the participants in this story, see the article in the Feb. 7 Delta Farm Press.

e-mail: erobinson@primediabusiness.com