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Title: How Well Does Zone Sampling Based On Soil Electrical Conductivity Maps Represent Soil Variability

Author
item Shaner, Dale
item KHOSLA, RAJ - COLORADO STATE UNIVERSITY
item Brodahl, Mary
item Buchleiter, Gerald
item FARAHANI, HAMID - ICARDA

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/8/2008
Publication Date: 10/1/2008
Citation: Shaner, D.L., Khosla, R., Brodahl, M.K., Buchleiter, G.W., Farahani, H. 2008. How Well Does Zone Sampling Based On Soil Electrical Conductivity Maps Represent Soil Variability. Agronomy Journal 10/01/2008

Interpretive Summary: One of the needs in site-specific crop management is to map soil heterogeneity quickly and inexpensively. There are two major methods for mapping soil heterogeneity: grid sampling and zone sampling. Grid sampling is done by collecting soil samples from a number of points across a field and extrapolating from that information to the whole field. However, grid sampling is often too expensive for most farmers because of the high number of samples. Zone soil sampling is a method in which a field is divided into homogenous areas using an easy to measure ancillary attribute such as apparent soil electrical conductivity (ECa) and a few samples are taken from each zone. A study was done to determine how well zone sampling predicted the soil gathered from grid sampling. Approximately 80% of the samples in the grid sites that were more than 10 m from the zone boundaries were classified correctly. These results support the utilization of ECa-directed zone sampling as an alternative to grid soil sampling to map soil heterogeneity within a field.

Technical Abstract: Zone soil sampling is a method in which a field sampling is based on identifying homogenous areas using an easy to measure ancillary attribute such as apparent soil electrical conductivity (ECa). This study determined if ECa-directed zone sampling in two fields in northeastern Colorado could correctly predict soil texture and organic matter patterns of samples taken by a more intensive grid sample method. Each field, which were predominantly Bijou loamy sand (coarse loamy, mixed, superactive, mesic Ustic Haplargids), Valentine sand (mixed, mesic Typic Ustipsamments), was divided into three ECa zones and soil texture and organic matter content in the top 30 cm of soil were measured. There was a significant difference in the soil texture and organic matter content in both fields between ECa Zone 1 and Zone 3. Logistic regression showed that in both fields, approximately 80% of the grid sample sites in ECa Zone 1 were correctly predicted. Only 50% of the grid sample sites in ECa Zone 3 were correctly predicted in one field whereas 77% of the grid sites in ECa Zone 3 were correctly predicted in the other field. However, approximately 80% of the samples in the grid sites > 10 m from the zone boundaries were classified correctly as compared to the samples that were <10 m from the boundary in which only 50-54% were classified correctly . These results support the utilization of ECa-directed zone sampling as an alternative to grid soil sampling if the transition zones are avoided.