SOIL PENETRATION RESISTANCE WITH MOISTURE CORRECTION

Authors: NEWMAN, SYMANTHA - UNIV OF ILLINOIS; HUMMEL, JOHN

Submitted to: American Society of Agricultural Engineers Meetings Papers
Publication Type: Proceedings
Publication Acceptance Date: 8/3/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary: As agricultural tractors and field equipment get larger, the concern about soil compaction increases. Larger land areas being farmed by the same set of machinery increases the possibility that field operation will occur when soil is easily compacted. Instrumentation is needed to measure when soil is compacted to a level that, without additional tillage, will restrict crop root growth. Furthermore, instrumentation is needed that can acquire data across a range of soil types and soil moisture contents, and provide a measure of compaction that is independent of soil moisture content. This paper reports on an attempt to marry a USDA-Agri. Res. Ser. designed and patented soil moisture sensor with a soil cone penetrometer to address this need. The instrument uses a fiber optic bundle to transmit light down the penetrometer shaft and through a specially designed penetrometer cone onto the soil surface. Light reflected from the soil is transmitted back up the shaft to the soil surface for analysis and moisture prediction. Cone penetration force, measured in the same manner as with a conventional penetrometer, can then be adjusted to a standard soil moisture level. This laboratory study reports on the development of a force/moisture relationship for three surface agricultural soils in Illinois, and indicates that adjusting cone penetrometer force to compensate for soil moisture is feasible. Commercialization of this concept could significantly increase the usefulness of soil penetration resistance data, and lead to reduced primary tillage when used to measure soil compaction.

Technical Abstract: The objective was to modify a standard soil cone penetrometer to allow the measurement of soil moisture content simultaneously with penetration resistance. The device used a near infrared reflectance soil organic matter(OM)/soil moisture sensor in conjunction with a bifurcated fiber optic cable which transmitted the signal from the sensor through the penetrometer to the soil and back to the sensor. Moisture prediction was accomplished at the site of penetration resistance. Test results indicated that through use of a force prediction relationship, moisture effects could be removed from the penetration resistance values. The spectral reflectance sensor was able to predict moisture content while stationary and while traversing through the soil at 2.5 mm/s within +2.29% and +2.03%, respectively, using partial least squares regression (PLSR). Using multiple linear regression (MLR), the data allowed the OM sensor to accurately estimate moisture content while stationary and while traversing through the soil#s profile within +1.17% and +0.83%, respectively. The force prediction equation for the data over the entire range of soil type/moisture content for all methods of estimating moisture content yielded correlation coefficients of 0.895 or higher. Commercialization of this concept could significantly increase the usefulness of soil penetration resistance data. Data collected at different times during a growing season, or even during different seasons could be reduced to a single moisture level.