Automated mapping of the soil pH, potassium and mechanical impedance for site -specific management
Abstract
Site-specific farm management is a growing practice in modern agriculture. In many cases, implementation of developing technology has beneficial economic and environmental impacts. Analysis of soil properties is a key portion of the site-specific decision making process. On-the-go measurements of physical and chemical soil properties have the potential to increase soil map accuracy at a relatively low cost. Determination of soil pH is one application where improved mapping may be beneficial. A prototype automated soil sampling system has been created and tested to utilize combination, flat-surface, ion-selective electrodes to measure soil pH at field moisture content. Operated with a laptop computer, the automated system uses a designed mechanism to collect georeferenced soil samples. The modified procedure involved measurement of soil pH directly on naturally moist soil samples. Resulting standard deviation of measurement error was found to be 0.38 pH. The standard laboratory procedure (measurement of soil pH in 1:1 weight-to-weight soil-water solution) performed on the same set of samples resulted in 0.24 pH standard deviation. However, agroeconomic analysis identified potential benefits of the introduced technology. It was found that at high field variability of soil pH (CV > 9%), use of automated mapping to determine variable lime application rates is economically beneficial. At the same cost of soil sampling, automated measurements allowed higher mapping accuracy due to increased sampling density. Ion-selective electrodes similar to those used for pH are commercially available for potassium measurements. Laboratory experiments indicated high correlation (R2 = 0.84) between potassium ion activity measured with these electrodes and potassium ion concentration measured using atomic-absorption spectroscopy in 1:1 soil solutions. The automated soil-sampling system was designed to use any flat-surface ion-selective electrodes. Therefore, on-the-go measurement of potassium content along with soil pH is feasible. Finally, mechanical resistance is another important soil property with spatial variation. A vertical smooth blade with an array of strain gauges was designed to continuously measure mechanical impedance of soil at multiple depths. Field experiments indicated that cone penetrometer resistance averaged for certain depth intervals (0–15 cm, 15–25 cm, and 25–30 cm) and a particular treatment (no-till or chiseled soil) was correlated (R2 = 0.95) to the corresponding soil resistance estimated using the vertical smooth blade.
Degree
Ph.D.
Advisors
Morgan, Purdue University.
Subject Area
Agricultural engineering|Soil sciences
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