Wider adoption of remote imagery in agriculture has always been dogged by some critical shortcomings. First, it can prove complicated to interpret and turn into activity in the field. Second, the turnaround time from when an image is taken to when action is possible often has exceeded what’s of value to the grower.
This is quickly starting to change in some regions, in particular California, where crop values are higher, crops are more diverse, and the growing season is longer. One individual fully on the imagery bandwagon is Keith Clark, a consultant who operates in the San Joaquin Valley town of Lemoore.
Imagery is helping Clark’s clients – agronomic consultants to growers – make better input decisions in-season on cotton and postharvest decisions on soil amendments on a variety of crops. In other words, he is the consultant’s consultant on making imagery an important field managment tool.
Clark is employing the services of two imagery companies, Digital Globe and InTime, Inc., to provide the imagery. “I help my customers to ground truth the imagery, teach them how to use the prescription tools from the (imagery providers), and follow the process to the soil sampling after harvest,” says Clark.
When it come to imagery, cotton provides the best payback. In season, imagery help determine where and at what rates plant growth regulators (PGRs) and defoliants should be applied. Postharvest applications of amendments – gypsum and sulfur – are variably applied based on the same imagery data.
Images are generally taken every two weeks during the season, which runs from June through early September. Image turnaround is three days from order to delivery, so the action taken is usually on the fourth day after the order is placed.
“When we get the images, we are able to take them from the computer and load them onto a pocket PC and go out to the field, see what growth stage the cotton is at, and make a decision about a PGR application,” says Clark. “We gauge the amount to the growth rates of the plant in relation to the growth stage of the plant.”
Generally, says Clark, the PGR is needed in July during the heat of the summer. “The plant will grow at too fast a rate, so the PGR slows it down and the plant will set more squares and bolls. It also allows greater uniformity in growth throughout the field and the plants mature earlier,” he says.
The beauty of the images is two-fold – first, Clark uses them to identify vigorous growing zones, and can apply PGRs only to plants that are in those zones. Second, the companies supplying the imagery he utilizes also provide online prescription writing through easy-to-use Web tools.
Using either a Web-enabled PC or a regular comupter, Clark’s consultant customer, can write the prescription, create the file necessary to make the application, and e-mail the file to the applicator.
Modern remote imagery is easier for the consultant and farmer to interpret and understand. For example, InTime imagery features a 7-color scale ranging from dark green for high foliage to dark brown for low to no foliage. Digital Globe uses a 20-color scale with numeric values from 1 to 100, the color for 1-5 being no growth and the color for 95-100 a high foliage area.
“Frankly, farmers relate better to the colors,” says Clark. “A consultant may be able to gain some additional vigor infomation based on the number scale, but overall the easiest way to understand it is to use the color.”
The imagery is also useful for determining where and when to apply defoliant in advance of harvest, and for determining the most economical application of soil amendments.
“Once the crop is harvested, we go back over the series of three to five images we took and determine what areas to soil sample,” says Clark. “We evaluate the nutrient content of the soil and make a determination where soil amendments need to be placed. We can generally do a better job for the farmer using the imagery.”
The gypsum and sulfur amendments used in California can cost from $60 to $100 per acre, and Clark says it’s possible to cut the total cost in half in most cases. “We’ll apply the full rate to problem areas and nothing to the best areas,” says Clark.
Grower savings achieved in PGR applications range from 30% to 50% and from 15% to 30% in defoliants.
And the agronomic benefits are strong as well, says Clark. Some local growers averaged five bales per acre on the their best land in 2004. “It was a great growing year, but that is an astounding amount of cotton,” says Clark.
Editor’s note: This article first appeared in the Winter 2004 Issue of PrecisionAg Special Reports.