The problem may be yield, topography, soil types or soil fertility. The solution, in many cases, is not as easy as recommending a specific practice to correct the problem.
A study by Carl Crozier, a North Carolina State University soil scientist, aims to give growers the information they need to decide how to use precision agriculture to fit the problem. The ultimate goal is correcting the problem in a site-specific way.
This fall and winter Crozier will be adding the yield map layer to information gathered from an aerial survey to upgrade flood maps following the hurricanes that hit North Carolina in 1999.
“We have been basically surveying fields to identify the pattern of land shaping,” says Crozier, a North Carolina State University soil scientist. “We have in our mind an ideal, the one that was formed when the wetland forest in this area was drained and ditches were dug.”
Often in the northeastern part of North Carolina the problems are the result of drainage systems that have received minimal attention since the initial land clearing.
Working from a database that shows the elevation of every field in northeastern North Carolina, Crozier identifies the crowns and ditches in the Tidewater region. “What we generally see when we look at fields are depressions and a crown of 2 feet.”
He believes the ideal 300-foot-wide field will have a 9-inch crown in the middle and a one half percent slope.
The second phase of the study is to look at grain and cotton yield maps for these same fields and see if yield reductions can be associated with too high of a crown or too low of crown in the field.
Crozier will be looking at both the highest and lowest yielding fields and searching for a correlation between yield variability and topography as well as yield variability and soil fertility. “There are different layers of information, which might explain yield variability. A certain amount of the time yield is associated with fertility; a certain amount of time, topography; and at other times, soil type.
“If we can come up with generalizations about how often this information is useful, it might help farmers target different problems in the field,” Crozier says.
“The goal is to help farmers decide if improving the drainage network is worth the expense,” Crozier says. “This type of information could help them decide if re-leveling or putting in drainage structures will be the most cost-effective practice.”
Crozier has been working with representatives of the Spectra I.S. company, using precision land-leveling devices.
In collecting large sampling sizes of farm fields, Crozier has found isolated spots where drainage problems have meant a 50-percent yield reduction. Crozier is attempting to characterize the percentage of land area that might be affected negatively by over- or under-drainage.
“If only 5 percent of the land is severely impacted, the producer might choose to leave it as it is or do some spot corrections, rather than trying to level whole fields,” Crozier says.
The aim is to give the farmer the tools to make the decision about improvements.
“We’re trying to come up with some guidelines when different type of information might be useful,” Crozier says.
He points out that getting the information is only the first step for farmers. “Even with this topographic information, a farmer would have to invest in software or expertise to create maps,” Crozier says. “There’s a cost to learning to use or manage the data.”
“By establishing guidelines for when and how to use the information, we might end up with regional recommendations on how to best use precision agriculture,” Crozier says.
For example, if the variability is due to soil type and topography, grid sampling might not correct the problem because yields may be more limited by soil physical properties than by chemical aspects of fertility. This information could be used to modify soil-sampling strategies to coincide with landscape features such as soil types or topography.
Conventional grid sampling should be useful where the physical landscape is more uniform.
The North Carolina Corn Growers Association and the Potash and Phosphorous Institute are funding the study.