Strip Intercropping: Yields and "Bugs"
Table 7 shows results of strip intercropping trials on the farms of Paul and Karen Mugge, Sutherland, and Jeff and Gayle Olson, Mt. Pleasant. The numbers at the top of the table were collected by the cooperators themselves, while the yields at the bottom of the table were hand harvested by ISU. Corn yielded better in strips than in large, single-crop field blocks, and the corn at the strip borders yielded better than corn in the center of the strips. That was expected and reflects the biological efficiency that is part of strip intercropping's attraction. Paul planted 28,000 seeds per acre in his sole-crop blocks and about 35,000 in corn strips. The low harvest stand measured in row 4 of the strips makes him wonder if he might have had a faulty planter unit.
Figure 4. Comparison of rootworm barrier methods on corn in strip row bordering previous corn strip
Soybean yields apparently suffered in strips at Olsons', and the unreliability of the combine monitor forced Paul Mugge to throw out his soybean data. Soybean yields averaged the same or slightly higher in strips over three years of comparisons by six cooperators, and corn yields averaged ten bushels higher in strips than field blocks for those 18 site-years.
The current challenge in strip intercropping appears to be bugs. Maybe strips are no more vulnerable to insects than is sole-cropping, but PFI is working with entomologists and agronomists from ISU and South Dakota State University to answer related questions. There were three suspected culprits in 1996: grasshoppers, common stalkborers, and corn rootworm beetles.
Paul and Karen Mugge, in northwest Iowa, have had problems with grasshoppers on the whole farm for the past two years. Paul has observed grasshoppers eating oat regrowth after small grains harvest, and these hungry pests moved right over into the soybeans after finishing off the oat strips. Failure of the combine monitor prevented Paul from measuring the effect of grasshoppers on soybean strips. Intercropped corn yields next to oat strips were still higher than in the center of the corn strips.
Common stalkborer may also have used strips as highways to travel into the field from the grassy borders where their eggs hatch. Any stray grass left between strips can also harbor these stalkborer eggs and young larvae. PFI coordinator Rick Exner and ISU entomologist Kris Giles applied an experimental biological control for stalkborers when they were migrating out of field borders on Jeff and Gayle Olson's farm. That information is being evaluated. Next year New Melleray Abbey may use its flame cultivator to singe the grass in field borders where stalkborers reside in spring.
Finally, SDSU entomologist Mike Ellsbury continued his study of corn rootworms in strip intercropping. In 1995, Mike found evidence that western corn rootworm larvae were migrating underground into the first row of a corn strip next to the previous year's corn. In 1996, those data did not show strong trends. However, Mike did test several methods for interrupting the rootworm migration, and those results appear in the side-bar and Figure 4.