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The Spatial Distribution of Soybean Cyst Nematode in Relation to Soil Texture and Soil Map Unit

^a Dep. of Plant Pathol., 351 Bessey Hall, Iowa State Univ., Ames, IA 50011
^b Cent. for Precision Agric. Syst., Washington State Univ., 24106 North Bunn Rd., Prosser, WA 99350
^c SAS Inst., Cary, NC 27513
^d Dep. of Entomol., 243 Nat. Sci. Bldg., Michigan State Univ., East Lansing, MI 48824

View larger version (40K): [in a new window]   Fig. 1. (A) Nested design for the collection of soil samples. Samples were collected at the indicated distances in random directions within grid cells of 50 by 50 m. (B) Location of sampled sites and soil series present in Field A. Crosses indicate the location of samples collected for the determination of soybean cyst nematode population density; black circles indicate which of those samples were also used for soil particle size analysis. Soil series are (1) Newaygo sandy loam, (2) Conover loam, (3) Brookston loam, (4) Breckenridge sandy loam, and (5) Belding sandy loam. Soil series map was digitized from Threlkeld and Feenstra (1974). Spatial distribution of (C) sand, (D) clay, and (E) silt percentages in the soil as interpolated by ordinary kriging within the area sampled. The shadings in C, D, and E represent percentage ranges. (F) Soil type delineation determined based on the proportion of sand, silt, and clay. Soil types are (1) loamy sand, (2) sandy loam, (3) loam, and (4) sandy clay loam.

View larger version (64K): [in a new window]   Fig. 2. (A) Location of sampled sites and soil series present in Field B. Crosses indicate the location of samples collected for the determination of soybean cyst nematode population density (see Fig. 1A); black circles indicate which of those samples were also used for soil particle size analysis. Soil series are (1) Newaygo sandy loam, (2) Brookston loam, and (3) Berville loam. Soil series map was digitized from Threlkeld and Feenstra (1974). Spatial distribution of (B) sand, (C) clay, and (D) silt percentages in the soil as interpolated by universal kriging within the area sampled. The shadings in B, C, and D represent percentage ranges. (E) Soil type delineation determined based on the proportion of sand, silt, and clay. Soil types are (1) loamy sand, (2) sandy loam, and (3) sandy clay loam.

View larger version (32K): [in a new window]   Fig. 3. Box plots of soybean cyst nematode (A) cyst population density and (C) eggs per cyst in Field A and (B) cyst population density and (D) eggs per cyst in Field B. The y axis indicates the sampling time: P '99, planting 1999; H '99, harvest 1999; P '00, planting 2000; and H '00, harvest 2000. The sample mean is indicated with a dashed vertical line and the median with a solid vertical line in each box. Significant differences among the means at different sampling times within each field are indicated with lowercase letters. Mean comparisons were performed on logarithmic-transformed data; original data are shown for clarity. Means with the same letter were not significantly different (protected LSD, 0.05 significance level).

View larger version (20K): [in a new window]   Fig. 4. Semivariograms of (A) sand and (B) clay percentage in the soil in Field A, and (C) sand and (D) clay percentages in the soil in Field B. Black circles indicate omnidirectional empirical semivariogram, the solid line indicates the theoretical model fitted by means of least squares, and the dashed line is the sample variance.

View larger version (15K): [in a new window]   Fig. 5. Soybean cyst nematode mean cyst population density [log10 (cysts 100 cm–3 of soil + 1)] ± standard error by soil type in Field A (open circles) and in Field B (closed circles) at (A) planting 1999, (B) harvest 1999, (C) planting 2000, and (D) harvest 2000. Soil types are sandy clay loam (SCL), sandy loam (SL), loamy sand (LS), and loam (L). Means with the same letter were not significantly different (protected LSD, 0.05 significance level).

View larger version (47K): [in a new window]   Fig. 6. Relationship between soybean cyst nematode cyst population density [log10 (cysts 100 cm–3 of soil + 1)] and the proportion of each soil fraction in the sample. Means ± standard error for Field A (open circles) and for Field B (closed circles) are indicated. The left column (A, B, C, and D) corresponds to the percentage of sand, the central column (E, F, G, and H) corresponds to clay percentage, and the right column (I, J, K, and L) corresponds to silt percentage at (A, E, and I) planting 1999, (B, F, and J) harvest 1999, (C, G, and K) planting 2000, and (D, H, and L) harvest 2000. Regression curves fitted are indicated as solid lines (Field B) and dashed lines (Field A) where significant (0.05 significance level). Regression coefficients are shown in Table 3.

View larger version (53K): [in a new window]   Fig. 7. Relationship between soybean cyst nematode eggs per cyst [log10 (eggs per cyst 100 cm–3 of soil + 1)] and the proportion of each soil fraction in the sample. Means ± standard error in Field A (open circles) and in Field B (closed circles) are indicated. The left column (A, B, C, and D) corresponds to sand percentage, the central column (E, F, G, and H) corresponds to clay percentage, and the right column (I, J, K, and L) corresponds to silt percentage at (A, E, and I) planting 1999, (B, F, and J) harvest 1999, (C, G, and K) planting 2000, and (D, H, and L) harvest 2000. Regression curves fitted are indicated as solid lines (Field B) and dashed lines (Field A) where significant (0.05 significance level).

View larger version (36K): [in a new window]   Fig. 8. Cross-correlograms of soybean cyst nematode cyst population density and percentage sand (solid line) or clay (dashed line) in the soil in (A–D) Field A and (E–H) Field B. (A and E) planting 1999, (B and F) harvest 1999, (C and G) planting 2000, and (D and H) harvest 2000. Linear correlation coefficients for cyst density with sand and clay are indicated.

View larger version (41K): [in a new window]   Fig. 9. Cross-correlograms of soybean cyst nematode eggs per cyst and percentage sand (solid line) or clay (dashed line) in the soil in (A–D) Field A and (E–H) Field B. (A and E) planting 1999, (B and F) harvest 1999, (C and G) planting 2000, and (D and H) harvest 2000. Linear correlation coefficients for eggs per cyst with sand and clay are indicated.