David Franzen 1
It is unusual for a study to have examined soil-sampling density before the 1970’s. It is even more unusual for that study to continue for a period of nearly forty years. Yet, the Mansfield data set sampling by the late Dr. Ted Peck is one data set that spans a time span from 1961 until 1999. This field was sampled in an 80-foot grid (5-rods) in 1961, then again in 1976, 1982, 1986, and then annually from 1988 until 1999. The original 1961 data set (Figure 1) was the inspiration for the original discussion of sampling density to fulfill the goal of finding the “central tendency” of a field through the book chapter “Field sampling for soil testing” in the 1967 edition of Soil Testing and Plant Analysis, a Soil Science Society of America special publication (Peck and Melsted, 1967). The study also resulted in the initial soil sampling recommendation of eleven samples per forty acres to help achieve the field central tendency for P, K and soil pH testing in Illinois.
Through these data, there are several pieces of information that will be of value. First is the rate of change of P and K tests over time. Because each field is managed by the University of Illinois farm managers, there is a good record of yields over the time span of study. By comparing estimates of P and K removal by crop with the record of P and K applied, the buildup rate for each field can be estimated. In addition, from about 1988 until 1998, no additional P and K was applied. An examination of the change in P and K levels with time and crop removal will help determine the draw-down rate of change.
The second important value for this data is to follow the spatial pattern of soil pH, P and K levels over time. A distinctive, repeatable pattern of nutrients in a field might lead a sampler to sample a field more intensely at first, then rely on the pattern to direct future sampling in a less rigorous manner.
Thirdly, the data will be useful to compare zone sampling techniques based on relatively easy to obtain non-laboratory data, such as topography or soil EC sensors. The objective of this study is to summarize the sampling data in these fields and apply newer techniques to see if zone sampling has an application in fields such as these.
In the summer of 2006, the data archived on paper from both Mansfield and Thomasboro
were copied into Excel files. In addition, files were created for the differences
between years within each field of pH, P and K.
In the fall of 2006, elevation was measured in each field using a laser transit
device, using a grid at least as dense as the soil sampling 80-foot grid. In
addition, apparent soil EC was measured using a Geonics EM-38 magnetic unit following
crop harvest in a similar grid as used to measure elevation. Wet soil conditions
following soybean harvest at each field prevented the planned use of a
more robust and denser EC measurement using a Veris-EC sensor, however the EM-38
has been shown to yield similar map patterns if the density of measurement is
high enough.
During the next 12 months, the data will be further analyzed and summarized into a technical bulletin for use by the general public, and will be made available through the world-wide web.
Figure 1. Mansfield soil test levels, 1961.
Figure 2. Thomasboro, 1982, initial sampling.
Figure 3. Mansfield elevation overlayed with apparent EC from the use of an EM-38.
Figure 4. Thomasboro elevation overlayed with apparent EC from the use of an EM-38.
1Extension Soil Specialist, Department of Soil Science, North Dakota State University, Fargo, ND
Peck, T.R., and S.W. Melsted. 1967. Field sampling for soil testing. p. 25-35. In M. Stelley (ed.) Soil Testing and Plant Analysis. Part 1. SSSA Spec. Publ. 2, SSSA, Madison, WI.