Table 1
Tillage, crop rotation, and biocide treatment effects on Heterodera glycines population density (eggs/100 cm3 soil) at nematode suppressive soil at two field sites in Minnesota.
| Year | 2009 | 2010 | 2011 | 2012 | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Treatment | Pi | Pm | Pf | Pi | Pm | Pf | Pi | Pm | Pf | Pi | Pm | Pf | |
| Site 1 | |||||||||||||
| Tillage: | |||||||||||||
| No-tillage | 4,258 a | 4,442 a | 7,033 a | 4,853 a | 2,400 b | 5,664 a | 4,442 a | 2,507 a | 6,319 a | 4,621 a | 3,022 a | 11,666 a | |
| Conventional tillage | 4,393 a | 4,241 a | 8,547 a | 5,135 a | 3,378 a | 5,981 a | 4,622 a | 2,116 a | 6,457 a | 3,409 b | 2,510 a | 8,613 a | |
| Crop-Biocide: | |||||||||||||
| C-S-C-S, | no biocide | 3,881 a | 3,200 c | 2,250 b | 1,766 b | 1,102 d | 4,238 c | 2,263 c | 1,275 b | 1,175 d | 677 d | 1,114 c | 11,803 b |
| C-R-C-S | no biocide | 4,519 a | 3,350 c | 2,756 b | 1,480 b | 848 d | 1,394 d | 1,075 d | 678 c | 438 e | 345 d | 477 d | 6,975 c |
| S-S-S-S | streptomycin | 5,338 a | 5,452 a | 11,675 a | 6,609 a | 2,581 c | 4,938 bc | 3,556 b | 1,791 b | 6,488 c | 4,413 bc | 2,628 b | 6,209 c |
| S-S-S-S | captan | 4,013 a | 5,409 a | 10,444 a | 6,775 a | 4,131 b | 6,381 b | 4,334 b | 2,406 b | 9,181 b | 6,206 ab | 3,847 b | 9,781 bc |
| S-S-S-S | no biocide | 4,641 a | 4,847 ab | 9,794 a | 5,947 a | 2,828 c | 5,331 bc | 3,406 bc | 1,597 b | 6,506 c | 3,969 c | 2,666 b | 8,169 c |
| S-S-S-S | formaldehyde | 3,566 a | 3,794 bc | 9,825 a | 7,391 a | 5,856 a | 12,656 a | 12,563 a | 6,125 a | 14,541 a | 8,481 a | 5,866 a | 17,897 a |
| Overall means | 4,326 | 4,342 | 7,790 | 4,994 | 2,889 | 5,823 | 4,532 | 2,312 | 6,388 | 4,015 | 2,766 | 10,140 | |
| ANOVA (F-statistics): | |||||||||||||
| Tillage | 0.09 | 0.01 | 3.82 | 0.19 | 25.46* | 0.34 | 1.04 | 0.07 | 0.53 | 18.2* | 0 | 1.14 | |
| Crop-Biocide | 1.98 | 5.65*** | 23.08**** | 33.56**** | 32.2**** | 32.83**** | 38.2**** | 16.09**** | 75.89**** | 39.18**** | 33.03**** | 10.88**** | |
| Tillage × Crop-Biocide | 0.32 | 1.84 | 2.38 | 1.28 | 1.67 | 3.76** | 1.8 | 1.79 | 1.72 | 1.01 | 4.16** | 1.23 | |
| Site 2 | |||||||||||||
| Tillage: | |||||||||||||
| No-tillage | 139 a | 553 a | 1,146 a | 899 a | 519 b | 2,586 a | 2,892 a | 2,747 a | 6,708 a | 3,635 a | 2,368 a | 7,646 a | |
| Conventional tillage | 65 a | 539 a | 1,732 a | 803 a | 955 a | 2,893 a | 2,702 a | 2,467a | 6,205 a | 2,993 a | 2,634 a | 7,590 a | |
| Crop-Biocide: | |||||||||||||
| C-S-C-S | no biocide | 136 a | 106 b | 214 c | 64 b | 139 b | 1,381 b | 1,025 b | 1,363 b | 1,594 c | 806 c | 1,141 c | 8,231 a |
| C-R-C-S | no biocide | 123 a | 158 b | 91 c | 374 b | 72 b | 153 c | 163 c | 100 c | 125 d | 144 d | 197 d | 3,631 b |
| S-S-S-S | streptomycin | 92 a | 1,053 a | 1,586 b | 802 a | 1,064 a | 4,506 a | 3,919 a | 4,322 a | 10,369 ab | 3,988 b | 3,188 b | 7,991 a |
| S-S-S-S | captan | 98 a | 809 a | 2,430 ab | 1,439 a | 1,203 a | 4,113 a | 5,150 a | 4,856 a | 12,563 a | 7,581 a | 5,859 a | 11,325 a |
| S-S-S-S | no biocide | 61 a | 602 a | 2,873 a | 1,579 a | 1,208 a | 3,544 a | 2,781 a | 3,347 a | 7,631 b | 4,050 b | 2,119 b | 6,913 a |
| Overall means | 102 | 546 | 1,439 | 851 | 737 | 2,740 | 2,797 | 2,607 | 6,457 | 3,314 | 2,501 | 7,618 | |
| ANOVA (F-statistics): | |||||||||||||
| Tillage | 3.9 | 0.41 | 2.07 | 1.64 | 10.56* | 0.96 | 1.21 | 0.89 | 3.85 | 0.25 | 2.87 | 0.02 | |
| Biocide-crop | 7.18*** | 22.01**** | 7.77*** | 22.45**** | 34.09**** | 20.98**** | 29.94**** | 54.87**** | 37.73**** | 28.89**** | 6.09** | ||
| Tillage × Crop-Biocide | 0.09 | 0.26 | 1.08 | 0.15 | 4.67** | 1.17 | 1.24 | 0.69 | 0.36 | 1.25 | 0.43 | 0.57 | |
1 Note: C, corn; S, SCN-susceptible soybean, R, SCN-resistant soybean, and the letters in the order represent the crops from 2009 to 2010. Planting (Pi), midseason (Pm), and harvest (Pf); the data are main effect of the split-plot experiment with tillage as main plots and crop-biocide treatments as subplots with four replicates. The mean values followed by the contrasting letters in the column are significantly different according to the LSD test at P < 0.05. *P < 0.05; **P < 0.01; ***P < 0.001; ****P < 0.0001.
Table 2
Interactive effects of tillage and crop-biocide treatments on the population density (eggs/100 cm3 soil) of Heterodera glycines.
| Treatments | Pf2010, Site 1 | Pm2012, Site 1 | Pm2010, Site 2 | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Crop | Biocide | No-tillage | Conventional tillage | No-tillage | Conventional tillage | No-tillage | Conventional tillage | ||||||
| C-S-C-S | No biocide | 5,175 | ab A | 3,300 | c A | 959 | c A | 1,269 | cd A | 141 | b A | 138 | c A |
| C-R-C-S | No biocide | 1,238 | d A | 1,550 | d A | 219 | d B | 734 | d A | 131 | b A | 13 | c B |
| S-S-S-S | Streptomycin | 3,300 | c B | 6,575 | b A | 2,744 | b A | 2,513 | b A | 322 | a B | 1,806 | bc A |
| S-S-S-S | Captan | 5,538 | b A | 7,225 | b A | 5,438 | a A | 2,256 | bc B | 1,047 | a A | 1,359 | a A |
| S-S-S-S | No biocide | 4,275 | bc A | 6,388 | b A | 2,988 | b A | 2,344 | bc A | 956 | a A | 1,459 | ab A |
| S-S-S-S | Formaldehyde | 14,463 | a A | 10,850 | a A | 5,788 | a A | 5,944 | a A | ||||
1 Note: C, corn; S, SCN-susceptible soybean; R, SCN-resistant soybean, and the letters in the order represent the crops from 2009 to 2010. Pm = midseason, and Pf = harvest. The data are means of four replicates. The values followed by the contrasting lowercase letters in the same column or the values followed by the contrasting uppercase letters in the row within the same sampling time are different at P < 0.05 according to LSD test.

Figure 1:
Tillage, crop rotation, and biocide treatment effects on soybean yield at two field sites infested with Heterodera glycines in Minnesota. (A) Tillage treatment at Site 1. (B) Biocide and crop sequence treatments at Site 1. (C) Tillage treatment at Site 2. (D) Biocide and crop sequence treatments at Site 2. CT = Conventional tillage, and NT = No-tillage. The CSCS, CRCS, and SSSS are 4-yr crop sequences where C is corn, S is SCN-susceptible soybean, R is SCN-resistant soybean, and the consecutive letters represent the crops in 2009, 2010, 2011, and 2012, respectively. Illustrated are mean (±1 SE) main effects (n = 4). Bars annotated by contrasting letter(s) within the same year are different according to LSD test at P ⩽ 0.05.

Figure 2:
Egg population density of Heterodera glycines and soybean shoot dry weight in the greenhouse assay of soil from plots treated with tillage, crop rotation, and biocides at two field sites in Minnesota. (A) Egg population density at Site 1. (B) Egg population density at Site 2. (C) Soybean shoot dry weight at Site 1. (D) Soybean shoot dry weight at Site 2. The data are means of all tillage and crop-biocide treatments with four replicates (n = 48 at Site 1, and n = 40 at Site 2). The lines above the bars indicate the standard error. Bars annotated by contrasting letter(s) within the same year are significantly different according to LSD test at P ⩽ 0.05.
Table A1.
Plot treatments.
| Crop sequence | |||||
|---|---|---|---|---|---|
| Treatment | 2009 | 2010 | 2011 | 2012 | Biocide treatment |
| 1 | C | S | C | S | No |
| 2 | C | R1 | C | S | No |
| 3 | S | S | S | S | Streptomycin, every year |
| 4 | S | S | S | S | Captan, every year |
| 5 | S | S | S | S | No |
| 6 | S | S | S | S | Formalina |

Figure A1:
Field map of sample Site 1 in 2012.