Cup Method

Introduction:

In 1967, the NCR-13 representatives using volume measurement elected to adopt a standard-size, stainless-steel scoop to minimize the following problems:

1.  Contamination of soil samples,

2.  Wear of the scoop and variation among laboratories.

The committee members also decided to continue using the weight-volume basis of reporting soil test levels since soil testing with these terms has appreciable farm acceptance in the North Central Region. The usual

layman term is “pounds per acre,” and conversion to the metric system can be pp2m or ppm, designated with an asterisk to indicate scoop measurement.

Studies show that the 0.85 cc size scoop approximates a 1-gram measure of a typical soil. This is an empirical conclusion arrived at from the observation of several hundred volume/weight measurements on

a wide range of soils.

The typical soil is defined as a medial silt-loam texture with 2.5 percent organic matter crushed to pass a 10-mesh screen. The soil BD density of crushed, typical soil approximates 1.18, which is compared with 1.32 for undisturbed soil.

Experience with the 0.85 cc scoop shows that soil test results on a sample measured with such a scoop, when compared to a weighed sample analysis, differ by a factor equal to the difference in bulk density of the soil samples.

Table 1 shows the specifications for standard soil scoops as adopted by the NCR-13 Regional Soil Testing and Plant Analysis Committee. The scoops are illustrated in Figure 1. 

The relationship of pulverized soil scoop weight with unpulverized field bulk density is above (r= 0.79).

There is close agreement between the scoop design and soil mass contained in the normal range of bulk density.

The choice of a routine, rapid and accurate technique for measuring soil amounts for soil testing is an arbitrary one. In the experience of the NCR-13 committee, the use of a scoop of the proposed size and shape will give soil test results comparable to weighed samples corrected for bulk density with a precision of plus or minus 10 percent.

However, upon their entry (i.e., soil BDs) into our database at the MSU Research Site, Lenawee County, the data were screened for inconsistencies using visual and regression procedures. These procedures included checks on the consistency of soil organic matter (SOM) concentrations and the soil BD data measured by cup method from single soil horizons. A high correlation (r= 0.95) verified that the values were comprised of a realistic range for most soils. Thus, when the BD was the only missing parameter, the soil profiles were maintained, and the BD was calculated using a pedo-transfer function of SOM.

And here is the novel of this method. Please, communicate with the author for detailed information.