A Model for Agro-Economic Analysis of Soil
V. I. ADAMCHUK email@example.com
Department of Biological Systems Engineering, University of Nebraska-Lincoln, Lincoln, NE 68583
M. T. MORGAN firstname.lastname@example.org
Department of Agricultural and Biological Engineering, Purdue University, West Lafayette, IN 47907
JAMES M. LOWENBERG-DEBOER Lowenberg-DeBoer@agecon.purdue.edu
Department of Agricultural Economics, Purdue University, West Lafayette, IN 47907
Abstract. Core soil sampling followed by laboratory analysis is the traditional method used to map soil
pH prior to variable rate application (VRA) of lime on cropland. A recently developed automated soil
sampling system capable of measuring soil pH on-the-go has signiﬁcantly increased sampling resolution.
However, adoption of such systems must be justiﬁed economically. This paper presents a method for
assessing the economic beneﬁt from automated mapping of soil pH prior to variable rate lime application.
In this work, geostatistical, agronomic, and economic methods were used to generate a comprehensive
numerical model for quantitative assessment of the net return over cost of liming for diﬀerent lime
management strategies. The strategies included: automated pH mapping, manual grid soil sampling, and
whole ﬁeld sampling used in combination with either variable or ﬁxed rate liming. The model was dem-
onstrated using a simulated ﬁeld with known average pH and semivariogram model. The analysis showed
the largest beneﬁt ($6.13 ha
) from using VRA with automated soil pH mapping versus VRA
based on 1 ha (2.5 acres) manual grid point sampling for the selected simulated ﬁeld conditions. A
sensitivity analysis demonstrated that for a wide range of ﬁeld conditions and crop prices, VRA plus
automated mapping promises higher relative beneﬁts than VRA based on either manual grid point or grid
Keywords: automated mapping, soil pH, variable rate liming
Among factors aﬀecting crop production, soil properties play a key role. Unlike
weather or topography, the availability of soil nutrients can be adjusted via appli-
cation of fertilizers. Soil pH is a measure of soil acidity/alkalinity, which deﬁnes the
soil environment and aﬀects nutrient availability. If soil pH deviates above or below
an optimum range, crop performance may suﬀer. When soil pH falls below a critical
level, lime application is usually recommended to decrease acidity (Mengel, 1997).
The amount of applied material is expected to improve soil productivity and provide
a yield increase that would cover the cost of liming (material, soil sampling, analysis
and lime application) (Brouder and Lowenberg-DeBoer, 2000).
Soil pH exhibits spatial variation with coeﬃcient of variation (CV) values typically
being about 10% (Wollenhaupt et al., 1997). Clay et al. (1999) illustrated that soil
Precision Agriculture, 5, 111–129, 2004
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