HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Abstract Full Text Free Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Brouder, S. M. Articles by Morris, D. K. Search for Related Content PubMed Articles by Brouder, S. M. Articles by Morris, D. K. GeoRef GeoRef Citation Agricola Articles by Brouder, S. M. Articles by Morris, D. K. Related Collections Spatial Variability Site-Specific Analysis

Mapping Soil pH

Accuracy of Common Soil Sampling Strategies and Estimation Techniques

^a Agronomy Dep., Purdue Univ., 915 W. State Street, West Lafayette, IN, 47907
^b Biological and Agricultural Engineering Dep., 123 E.B. Doran Bldg., Louisiana State University, Baton Rouge, LA 70803

View larger version (29K): [in a new window]   Fig. 1. (a) Absolute and (b) standardized variograms for pH and (c) absolute and (d) standardized lime requirement (LR) based on point sampling densities of 5 (DPAC R and V) or 10 (all others) locations per hectare. Separate variograms are shown for fields that are not contiguous.

View larger version (18K): [in a new window]   Fig. 2. Standardized variograms for (a) pH and (b) lime requirement (LR) based on a point sampling density of 2.5 ha–1 (0.4-ha grid). Separate variograms are shown for fields that are not contiguous.

View larger version (38K): [in a new window]   Fig. 3. Comparison of actual DPAC (a, c, and e) pH and (b, d, and f) lime requirement (LR) values with values estimated by cross validation of block kriging based on either the most dense point sampling strategy (•, 10 [CP0.1ha] or 5 [P0.2ha] points ha–1) or a sparser strategy of 2.5 points ha–1 (P0.4 ha). Estimated CP0.1ha/P0.2ha values are from cross validation while estimated P0.4 ha values represent the combination of results from cross and jackknife validation.

View larger version (31K): [in a new window]   Fig. 4. Comparison of actual NEPAC pH (a) and lime requirement (LR: b) values with values estimated by cross validation of block kriging based on either the most dense point sampling strategy (•, 10 points ha–1 [CP0.1ha]) or a sparser strategy of 2.5 points ha–1 (P0.4 ha). Estimated CP0.1ha values are from cross validation while estimated P0.4 ha values represent the combination of results from cross and jackknife validation.

View larger version (28K): [in a new window]   Fig. 5. Comparison of actual DPAC Field R and V pH with pH estimated by either cross validation with replacement (•) or jackknife validation with independent data (). Cross validation estimates were derived following block kriging pH values collected at a density of 2.5 points ha–1 (P0.4 ha).

View larger version (44K): [in a new window]   Fig. 6. The under- or overestimation of pH and lime requirement (LR) following map development based on area composite (AC), point (P) or centers point (CP) sampling strategies for DPAC. Composite strategies include a research whole field (AC WF, all samples averaged), a commercial or true farm whole field (AC TF, subsets of samples representing a density of 1 ha–1 averaged), and 1-ha grid (AC 1 ha, all samples averaged on a ha–1 basis). Maps developed from point data use either the CP value of a given ha to represent the whole ha without any smoothing (No. Smth CP1ha), IDP = 2 applied to CP 1-ha data, or kriging applied to P 0.2 and 0.4 ha data. Box plots show error mean (...), median (—), 25th to 75th percentiles (), 10th and 90th percentiles (,), and 5th and 95th percentiles (•). A cross () next to the AC TF mean absolute error (MAE) indicates µAC TF 0 (p < 0.05). Underlined MAEs of other strategies indicates µother µAC TF (p < 0.05). All prediction efficiencies (PE) are calculated relative to AC TF, and underlined PEs indicate other TF (p < 0.05).

View larger version (46K): [in a new window]   Fig. 7. The under- or over-estimation of pH and lime requirement (LR) following map development based on area composite (AC), point (P) or centers point (CP) sampling strategies for NEPAC. Composite strategies include a research whole field (AC WF, all samples averaged), a commercial or true farm whole field (AC TF, subsets of samples representing a density of 1 ha–1 averaged), and 1-ha grid (AC 1 ha, all samples averaged on a ha–1 basis). Maps developed from point data use either the CP value of a given ha to represent the whole ha without any smoothing (No. Smth CP1ha), IDP=2 applied to CP 1 ha data, or kriging applied to CP 0.1 and P 0.4 ha data. Box plots show error mean (...), median (—), 25th to 75th percentiles (), 10th and 90th percentiles (,), and 5th and 95th percentiles (•). A cross () next to the AC TF mean absolute error (MAE) indicates µAC TF 0 (p < 0.05). Underlined MAEs of other strategies indicates µother µAC TF (p < 0.05). All prediction efficiencies (PE) are calculated relative to AC TF, and underlined PEs indicate other TF (p < 0.05).