How Well Does Zone Sampling Based on Soil Electrical Conductivity Maps Represent Soil Variability?

Abstract

In zone soil sampling a field is divided into homogenous areas using an easy to measure ancillary attribute (e.g., apparent soil electrical conductivity [ECa]) and a few samples are taken from each zone to estimate the soil characteristics in each zone. This study determined if ECa–directed zone sampling in two fields in northeastern Colorado could correctly predict soil texture and soil organic matter (SOM) 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), and Valentine sand (mixed, mesic Typic Ustipsamments), was divided into three ECa zones and soil texture and OM content in the top 30 cm of soil were measured. There was a significant difference in the soil texture and SOM 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 as Zone 3 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 to 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.

The arable farmer as the assessor of within-field soil variation

“…When the farmers were confronted with the data, they noted that the data did not always express the differences as they observed them. Shaner et al (2008) reported that if something differs little but is statistically significant, it is probably not of agronomic importance. This study has shown it may well be the other way round, with statistical testing being less sensitive than the farmer who has observed the agronomic importance over several years.…”

“…The budget allowed two fields of the last farmer interviewed to be sampled. To avoid boundary effects (Fleming et al 2000;Shaner et al 2008), farmers in this study were asked to indicate what buffer they would like to use near zone boundaries. In addition, parts of the field that were not of interest to the farmer, such as headlands, could be left out of the sampling scheme on the indication of the farmer.…”

“…Doerge (1999) defined a management zone as ''a sub-region of a field that expresses a relatively homogeneous combination of yield limiting factors for which a single rate of a specific crop input is appropriate.'' Management zones can be established by classifying yield and soil data according to a given set of rules using techniques such as cluster analysis, for example (Fraisse et al 2001;Shaner et al 2008).…”

The use of electromagnetic induction techniques in soils studies

“…At field and landscape scales, EC a maps have the potential to provide higher levels of resolution and greater distinction of soil types than soil maps prepared with traditional tools and survey methods provided there is significant variation in at least one of the factors that affects soil EC a (James et al, 2003;Jaynes, 1995Jaynes, , 1996aShaner et al, 2008). However, EC a surveys can also be used to confirm highly uniform soil properties throughout a field .…”

Precision turfgrass management: challenges and field applications for mapping turfgrass soil and stress

“…Thigpen (2007) applied PA principles to golf courses in the Carolinas (USA) for site-specific application of fertilizers using grid sampling (about 70 soil samples per fairway on a 15-20 m grid) and digital mapping of the data, but this is costly as each soil sample is analyzed separately. Shaner et al (2008) found that SSMU based soil sampling in agricultural fields was a viable option to grid sampling provided the soil sample locations were selected using appropriate protocols, such as those suggested by Corwin and Lesch (2005b). With SSMUs, there are several ways to reduce costs for site-specific application of fertilizers and amendments in PTM, such as:…”