Soil Sampling Techniques for Alabama, USA
A. N. THOMPSON
J. N. SHAW firstname.lastname@example.org
P. L. MASK, J. T. TOUCHTON AND
Department of Agronomy and Soils, Auburn University, 202 Funches Hall, Alabama, 36849 USA.
Abstract. Characterizing the spatial variability of nutrients facilitates precision soil sampling. Questions
exist regarding the best technique for directed soil sampling based on a priori knowledge of soil and crop
patterns. The objective of this study was to evaluate zone delineation techniques for Alabama grain ﬁelds
to determine which method best minimized the soil test variability. Site one (25.8 ha) and site three
(20.0 ha) were located in the Tennessee Valley region, and site two (24.2 ha) was located in the Coastal
Plain region of Alabama. Tennessee Valley soils ranged from well drained Rhodic and Typic Paleudults to
somewhat poorly drained Aquic Paleudults and Fluventic Dystrudepts. Coastal Plain soils ranged from
coarse-loamy Rhodic Kandiudults to loamy Arenic Kandiudults. Soils were sampled by grid soil sampling
methods (grid sizes of 0.40 ha and 1 ha) consisting of: (1) twenty composited cores collected randomly
throughout each grid (grid-cell sampling) and, (2) six composited cores collected randomly from a
~3 · 3 m area at the center of each grid (grid-point sampling). Zones were established from (1) an Order 1
Soil Survey, (2) corn (Zea mays L.) yield maps, and (3) airborne remote sensing images. All soil properties
were moderately to strongly spatially dependent as per semivariogram analyses. Diﬀerences in grid-point
and grid-cell soil test values suggested grid-point sampling does not accurately represent grid values. Zones
created by soil survey, yield data, and remote sensing images displayed lower coeﬃcient of variations
(%CV) for soil test values than overall ﬁeld values, suggesting these techniques group soil test variability.
However, few diﬀerences were observed between the three zone delineation techniques. Results suggest
directed sampling using zone delineation techniques outlined in this paper would result in more eﬃcient
soil sampling for these Alabama grain ﬁelds.
Keywords: soil sampling, grid sampling, management zones, spatial variability
Conventional soil sampling techniques utilize composited samples that typically
represent an entire ﬁeld. The traditional approach of applying uniform soil inputs
may result in an over and under supply of nutrients (Schnug et al., 1998). Excessive
nutrient applications reduce proﬁt margins and may result in detrimental eﬀects to the
environment, while under fertilization can limit crop yields and quality (Mohamed
et al., 1996). Precision soil sampling is used to identify ﬁeld-scale soil nutrient vari-
ability, and may allow producers to optimize inputs on a site-speciﬁc basis.
A high degree of spatial variability in soil nutrient levels is common (Penney et al.,
1996). Mallarino et al. (1999) showed soil test P and K on four Iowa corn (Zea mays L.)
and soybean (Glycine max L.) ﬁelds possessed a high degree of variability. The spatial
variability of soil properties inﬂuences plant growth (Tsegaye and Hill, 1998).
Precision Agriculture, 5, 345–358, 2004
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