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Plant samples were taken from a forty‐acre field in an 82.5 ft. grid at two sampling dates each year during a three‐year study. Soil samples were also taken in the same grid. Potassium (K) was analyzed in the plant samples using both a strong acid‐digest and a dilute (2%) acetic acid extraction. Plant K analyzed using both techniques were correlated with soil test K levels. Plant K analyzed with acid‐digestion was also highly correlated with the acetic acid‐extracted K. Mapping of early sampled plant K better represented soil K level patterns than later sampling. Plant K maps described areas of low K not represented by soil K level maps. Plant analysis may be useful in mapping areas for relative K nutrition where soil K analysis is not as descriptive of plant response to fertilizer K.

A long‐term (1968–1987) field study using corn‐soybean in rotation was conducted to compare the effect of rock phosphate (RP) and superphosphate (SP) at two lime levels on crop yield, soil availabl...

Variable rate fertilizer application being commercially performed today is most often based on a soil test map. The sampling density used to develop a map is often selected without background information regarding field soil test variability. The objective of this study was to determine how many samples should be taken from a field in order to locate and describe major areas of fertility affecting variable rate fertilizer applications. Two 40 acre fields were sampled in an 82.5 ft grid each fall from 1989 to 1992. Soil pH, Bray P1, and available K levels were determined on each sample and maps were made using inverse distance squared estimates. Data were taken from the samplings to represent a 165 ft and 330 ft grid pattern. Maps were developed from these less dense grids and compared with the 82.5 ft grid values. In 1992, a separate 220 ft grid sampling was taken. The 220 ft grid estimates were more highly correlated with the 82.5 ft grid values than were the 330 ft grid estimates, however, membership of 220 ft and 330 ft grid estimates within soil test categories were similar. Fertilizer P and K applications were made in one field following the 1992 sampling. Spring 1993 sampling showed the success of the 220 ft grid in directing a variable rate application of P and K. Comparisons to theoretical P and K applications directed by a 330 ft grid map showed the superiority of the 220 ft grid compared with the 330 ft grid.

Plant samples were taken in an 82.5 ft grid at an early and late sampling date in both 1991 and 1992 from a forty acre field in Illinois. Calcium (Ca) and magnesium (Mg) were analyzed on each sample and maps were made showing the levels of each nutrient within the field. Soil pH measurements were also made from each of the same sampling locations following each year of plant sampling. In the fall of 1991, a calcitic lime application was made using soil pH informations from the 1991 soil sampling to determine the boundaries and rate of the application. Calcium and Mg levels in 1991 roughly defined the area of low pH, except for the early sampled Mg levels. However, low Ca and Mg levels did not always indicate low pH levels. High Ca and Mg levels did not always indicate high pH levels. Following liming, plant Ca levels correlated better with soil pH and represented areas of high and low pH better than plant Mg. Other factors which influenced Ca and Mg levels may have been high levels of competitive...

Soil testing is viewed as the application of Soil Science Research. Thus, the history of soil testing is interwoven with the growth and development of soil science. Soil testing as a recognized sub‐unit of soil science emerged in the early 1940's with agriculture's transition from subsistence to production farming systems. Soil testing today enjoys popularity in direct relation to the research data base and the extent to which the crop production limiting soil factors are manageable and ameliorating materials are available at a reasonable cost.

Soil samples were obtained at 0–3, 3–6, 6–9 and 0–9 inch depths from experimental plots receiving five tillage treatments. Each of two samplers composited approximately six one‐inch cores from each plot. Soil samples were analyzed for acidity, P and K using routine analysis procedures in the University of Illinois Soil Testing Laboratory. Few significant differences were attributed to sampler and it was concluded that samplers using similar sampling techniques were obtaining soil samples from the same population. No significant differences in soil acidity at different depths were observed. The different tillage methods did significantly affect soil P at the 0–3 inch depth, but had no significant effect on soil P at deeper depths. Different tillage methods also significantly affected soil K values at different depths.