An evaluation of student proficiency in field estimation of soil texture

Abstract

This paper evaluates the ability of college students to estimate soil texture. The students (115 total) were enrolled in the Soil Morphology, Classification, and Survey classes taught at the University of Arizona from 1983 to 1987. Each semester the students were provided in the laboratory with 30 known reference samples during the first 2 wk of the semester. At the end of the third week, they were asked to estimate the percent sand, silt, and clay in 15 different samples, and also to identify the correct soil textural class. During the last week of the semester in 1983 and 1984, estimations on an additional set of 15 samples were made by 54 students. Simple linear regression equations and correlation coefficients were calculated that compared the student estimations of the percent soil separates to laboratory analyses. This paper further compares student data to estimates made by professional field soil scientists. The correlation coefficients and y intercepts at 3 wk, the end of the semester, and for professional soil scientists were respectively: percent sand—0.85/−3.9, 0.85/0.47, and 0.83/−2.5; percent clay—0.74/2.6, 0.79/4.5, and 0.81/3.1; percent silt—0.63/6.5, 0.55/8.1, and 0.72/5.7. The mean percent correct (using the 12 textural triangle classes) was 39% at 3 wk, 45% at the end of the semester, and 46% for professional soil scientists. Results indicate that with 3 wk of practice and the availability of good reference samples, students can attain a level of proficiency comparable to the professional soil scientists. Suggestions are made as to how some of these data could be used in grading field exams and soil judging contest score cards. Similar data collected on students in the basic soils class are also included in the paper.