J. M. Oolman

Document Type

Thesis - University Access Only

Award Date


Degree Name

Master of Science (MS)

Department / School

Plant Science

First Advisor

C.G. Carlson


Increased profitability occurs when crop nutrient needs are matched to soil productivity. Twenty-first century farming will be conducted by managing small field units (precision farming) rather than uniformly managing larger field sized units (conventional farming). This study was conducted to develop precision agronomic algorithms for crop producers, and analyze the usefulness of 21st century tools: Global positioning system (GPS), yield monitors and variable rate fertilizer applicators. Precision farming is managing large (40-640 acre) fields in small sized units (30-200 ft2), and applying fertilizer and/or herbicide at a specific rate in each small sized unit. Conventional farming is managing fields as 40- 640 acre units and applying fertilizer or herbicide at one rate to the entire field. Nitrogen application rates were varied by location within two 80 acre fields. Fertilizer applications were made based on site specific diagnosis, with the objective of eliminating over and under applications. GPS was used to determine the location during soil sampling and harvesting. Soil sampling was accomplished using a soil probe truck and GPS unit. Soil samples were collected on a 200 ft by 200 ft grid (15 subsamples within 20 ft of grid center) and chemically analyzed using SDSU Soil Laboratory recommendations for soil test procedures. Geostatistical analysis was accomplished to develop isoantecedent nitrogen, phosphorous and potassium maps of the fields. In this study only the rate of nitrogen was varied. A combine fitted with a GPS and a yield sensor was used to collect yield data to produce a field yield map for each field. A weigh wagon was used to verify and calibrate the yield sensor. Results showed no statistical difference between the yield of precision fertilized plots and conventionally fertilized plots. Precision fertilizer recommendations were made with the following recommendation equation. Nitrogen to be applied= 1.2 * (yield goal) - 40 - (soil test) (1994 SDSU accepted equation). Precision farmed fields received an average of 76 lbs/a of actual N. Subtract 100 lbs/a from 76 lbs/a equals 24 lbs/a of N fertilizer (Nitrogen fertilizer at $0.20/lb amounts to a cost savings of $4.80/a and gave the same crop yield). Precision farming using GPS reduced the amount of N fertilizer needed from 100 lbs/a to 76 lbs/a resulting in a cost savings of about $5.00/a. It also reduced the potential for runoff of nutrients into streams, wetlands, ponds, lakes and leaching into ground water: The GPS unit's ability to give location information rapidly, saved time when applying fertilizer, soil sampling and harvesting. When harvesting, the yield sensor was within 1% of weigh-wagon weights. The GPS unit was accurate to about 15 ft Precision farming with GPS results in crop production that is more profitable and environmentally sound.

Library of Congress Subject Headings

Precision farming
Soils -- Sampling




South Dakota State University



Rights Statement

In Copyright