August 7, 2003

 

Precision Farming and Soil Sampling Go Together

Zone soil sampling based on topography is an excellent way to get accurate measures of the soil nutrient variability in a field, according to North Dakota State University Extension Service agriculture engineer, Vern Hofman.

Accurate soil sampling is an important first step in precision farming systems, Hofman says. Variability is best determined by zone sampling as compared to intensive grid soil sampling, according to cooperative research of the Mandan USDA-ARS station, the Area IV Soil Conservation Districts and NDSU Extension Service. Residual soil nitrogen correlates well with topography. Variability can be determined with fewer samples and less cost than grid soil sampling. "This is an important factor for applying precision agriculture technology to the lower-value crops grown in the Upper Great Plains," Hofman says .

Initially, when the project began, intensive soil sampling found considerable variation across a 45-to 50-acre field. Variable rate application of fertilizer showed a positive return. With variable applications tailored to soil type, soil fertility and crop needs, the nutrient variability decreased. Consequently, Hofman says the economic benefit of variable rate applications decreased.

"But on fields with variable soil type and variable yield potential, variable fertilizer application will still show positive returns," Hofman says.

In years when crop production was reduced because of dry conditions, hail, or winter kill on the winter wheat, variable application of fertilizer showed a negative return. The next year considerable fertilizer variability showed up producing a positive return as the reduced crop left a considerable amount of fertilizer in the soil. Less fertilizer was applied as the fertilizer remaining in the soil could be used for the next years' crop production.

If a wet spring occurred after a dry growing season, some of the remaining nitrogen may move to a lower soil profile two to four feet below the soil surface. Small grain rooting systems are unable to retrieve nitrogen at this level. "However, sunflower does an excellent job of retrieving deeper soil nitrogen with its tap root system that reaches down four to five feet into the soil," Hofman says.

Retrieving deep soil nitrogen will help reduce the potential of nitrogen pollution of water supplies and retrieving the deeper nitrogen will help in producing more sunflower seed.

"Accurate soil sampling can help producers make the best use of precision farming technology to tailor applications of inputs to crop needs," Hofman says. "Applying fertilizer based on crop needs, soil type and moisture conditions can also reduce the pollution potential to the environment."

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Source: Vern Hofman, (701) 231-7240, vernon.hofman@ndsu.nodak.edu
Editor: Stephanie Renner, (701) 231-8371, srenner@ndsuext.nodak.edu