Remote Sensing Imagery as a Tool to Map High pH and Calcareous Soils on a Field Scale.
Natalia Rogovska, Alfred M. Blackmer, and Antonio P. Mallarino. Iowa State Univ, 2211 Agronomy Hall, Ames, IA 50011
Soybean is extensively grown in areas of the Midwest where fields often have soils that range from acid to highly alkaline and calcareous. Soybean plants tend to have yellow leaves and grow poorly on calcareous soils, and the symptoms are commonly described as iron deficiency chlorosis. The affected areas of the field sometimes can be significant, but symptoms often occur in complex and discontinuous patterns. The objective of this research was to explore how remote sensing imagery of soybean canopies and geographic information systems (GIS) technologies could be used to map and quantitatively describe the extent of high pH, calcareous soils on a field scale. Aerial images that consisted of visible red, green, blue, and near infrared bands were used to calculate green normalized difference vegetative index (GNDVI) and guide plant and soil sampling at nine sites. Ten to 16 sampling points were selected per field to include the widest range in GNDVI values. Soil samples were analyzed for pH and calcium carbonate equivalent (CCE). Soil pH and CCE were significantly related to GNDVI values in seven and six sites, respectively. A Soil Alkalinity Index (SAI) which combines pH and CCE in one value was defined as SAI = pH + 0.14CCE%. The SAI values were significantly related to GNDVI in all sites. Remote sensing imagery and GNDVI can be used to quantitatively describe distribution of high pH, calcareous soils on a field scale and used as an aid for a more effective zone sampling.