Precision Agriculture, 1, 217᎐234 1999
ᮊ 1999 Kluwer Academic Publishers. Manufactured in The Netherlands.
A NIR Technique for Rapid Determination of Soil
M. R. EHSANI, S. K. UPADHYAYA, D. SLAUGHTER, email@example.com
S. SHAFII AND M. PELLETIER
Biological and Agricultural Engineering Department, Uni
ersity of California, Da
is, CA 95616
Abstract. The objective of this investigation is to determine the possibility of rapidly sensing soil
mineral-N content using near infrared NIR reflectance. Simulation studies were conducted to
Ž. Ž .
determine the ability of Partial Least Squares PLS and Principal Components Regression PCR
techniques to relate NIR spectral data to soil nitrate content in the presence of interfering effects and
experimental noise. The simulation studies revealed that both PLS and PCR techniques were quite
robust in predicting soil nitrate content provided the calibration set included the same interfering
effects. These techniques failed completely if the prediction set contained interfering effects which were
not included in the calibration set. This implies that a site-specific calibration is necessary for this
technique to work successfully. Laboratory tests using Yolo loam and Capay clay soil samples as well as
verification tests using field soils Yolo loam and Capay clay mixed with nitrogen fertilizer indicated
that soil mineral-N content can be determined using the NIR technique provided site-specific calibra-
tion is used.
Keywords: precision farming, NIR-spectroscopy, nitrate sensor, soil mineral nitrogen
Introduction and literature review
Nitrogen is one of the key nutrients for enhancing agricultural production. Plants
usually take up nitrogen in the nitrate form. Since nitrate ions are extremely
mobile, they will leach to the ground water if not taken up by the plants.
Widespread nitrate contamination of ground water in recent decades has raised
several health ‘‘Blue-baby’’ syndrome and stomach cancer and environmental
algal bloom and greenhouse effect due to N O questions related to this nitrate
leaching problem Forman et al., 1985; Addiscott et al., 1991 . One major source of
nitrate leaching is fertilizer applied to crops and landscape FREP, 1991᎐92 .
Another important source of nitrate is intensive animal agriculture. These health
and environmental concerns have resulted in legislation restricting the allowable
concentration of nitrate in drinking water. The current public health standard for
drinking water in the U.S. is 44.3 ppm of NO 10 mg of N per liter FREP,
1991᎐92; Addiscott et al., 1991 .
Nitrogen fertilizer is usually applied uniformly throughout a field, although it is
known that soil fertility varies considerably within a field. Mineralization conver-
sion of soil organic matter to mineral-N by microbes , denitrification breakdown
of NO to N O by microbes , and leaching are some of the major reasons for
variability of nitrogen levels in soil. Since increasing nitrate concentration in the
ground water is a concern, it is wise to use techniques that avoid excessive use of