Update:
The original three-year proposal was supported by the Iowa Soybean Association for the first two years of the project, 2015 – 2017. Due to early termination of the project, it was not possible to fully document the benefits of monarch habitat establishment efforts; at least two growing seasons post-planting are needed to assess habitat establishment. The ISU College of Agriculture and Life Sciences provided the funding to complete 2018 (year three) data collection and data analysis over the three years of the project. The final data collection for 2018 was completed in August. This report qualitatively summarizes the results through 2018.

The objective of this project was to develop best management practices for converting existing non-native cool season grasslands to native pollinator/monarch habitat at bioreactor sites. Plot locations were sited at farms owned by Iowa Soybean Association members and site selection was facilitated with support from Iowa Soybean Association Staff, specifically Keegan Kult. The study included seven plots, all of which were grassland transitions (see Appendix A in full report). The approach for site preparation and planting generally complied with USDA-NRCS requirements for establishing pollinator habitat as of spring 2016. This approach utilized half a growing season to prepare a site for planting and, at the time, was an approach consistent with NRCS practices. In 2016 existing vegetation was mowed after August 1 and then sprayed with one or two applications of glyphosate in the fall, except one site where a grass selective herbicide was sprayed followed by an application of glyphosate. Sites were planted in fall (dormant season) of 2016.

Observations over the three years indicated that a half growing season of site preparation for a non-native cool season grassland to native habitat transition is insufficient site preparation to ensure native plant establishment. Relative establishment success of the plots is summarized in Appendix A (see attached full report). Photos of all plots for summer 2018 are included in Appendix B (see attached full report). Of the seven grassland transition sites in this study, one site is promising, with a high density of native forbs (wildflowers) establishing and a relatively low density of problematic weeds. Two sites have a medium density of native forbs with incomplete establishment due to weed pressure or native grass competition. The remaining four plots have poor or failed establishment. It appears the major factor limiting establishment at all seven sites is weed pressure.

Although native forb establishment was low overall, many forbs were observed. Relative forb density is summarized in Appendix C (see attached full report). It should be noted that a two year old planting (as ours is) will have higher densities of some species and lower densities of other species simply due to the natural pattern of the specific native species. Native species range from being ‘pioneer’ species that establish almost immediately to other ‘late successional’ species which may not be present at considerable densities until 5-10 years of prairie development. The application of this knowledge is that a balanced seed mix is desired. It would be shortsighted to suggest that a seed mix should contain far more of the species listed as ‘high density’ in year two post-planting. Native plant communities are dynamic and contain exceptional spatial and temporal variation. A good seed mix is a diverse seed mix. Overall, it appears native grass establishment is quite low. The only native grass consistently identified at the sites is canada wild rye and it is present at relatively low densities. Canada wild rye is a native cool season grass that is often present at high densities in a young establishing prairie so it is not surprising that it is easy to find but it should be present at higher densities than observed. Most native grasses are warm season grasses that grow vigorously in the summer. Native warm season grasses were observed at very low densities.

Three major factors must be considered and addressed before attempting to carry out a non-native cool season grass conversion at a bioreactor site: 1) current vegetation (all species) 2) weed seed bank/weed potential and 3) accumulated vegetation residue levels. These factors will play a critical role in determining relative percentage of overall native plant establishment and if not properly addressed will likely result in poor or failed establishment. It should also be noted that it is very difficult to know the weed seed bank/weed potential or the exact effects of site history. Based on guidance that has evolved since 2016, site preparation over two growing seasons is likely needed when executing a non-native cool season grass transition. This extended preparation completely kills the current vegetation, provides time to flush and kill multiple rounds of problematic weeds, depletes the weed seed bank/weed root stock, and provides flexibility to address any additional vegetation issues. The simplest method of thorough non-native grassland to native habitat site preparation is to grow herbicide resistant corn/soybeans for multiple years, ending on a soybean year but this is not an option on top of bioreactors as bioreactor management is incompatible with standard farming practices. Repeated herbicide applications is the desired site preparation approach for establishing native habitat on top of bioreactors.

If a grassland (which is not associated with a bioreactor) is to be converted to native habitat, corn/soybean transitions are always preferred over direct grassland transitions due to dramatic increases in native plant establishment. The previous statement is not an endorsement of removing corn/soybean acres from production (unless of course those acres are not economically productive). We strongly endorse the conversion of non-native grasslands to corn/soybeans for 2-3 years before establishing native habitat. Corn/soybean systems are annual systems with multiple disturbances each season (tillage, herbicides, harvest) and a highly competitive monoculture crop. Years of herbicides/tillage intentionally deplete the weed seed bank. Almost no perennial weeds are present in a corn/soybean field and only a select number of annual weeds can survive. Corn/soybean transitions are ideal because there is no existing vegetation to kill, the weed seed bank/weed potential is almost zero, and the remaining weeds are annual weeds which will not survive in the perennial system of a prairie.

A listing of potential site preparation options for non-native cool season grassland transitions is included below. Options 1 and 2 are ideal if a site can be cropped but these options do not apply to bioreactor sites. Option 3 is the preferred method if cropping is not feasible. Option 4 may work in some cases but will not target non-native cool season grasses when they are most vulnerable. Option 5 will likely result in low or highly variable establishment success while option 6 will almost always be a failure.

There are two scenarios in which a landowner may find themselves if they wish to establish native habitat on top of a bioreactor.
1. Bioreactor is being constructed
a. Wait until construction is complete and site has been graded to level
b. Follow option 3 or 4 from the list provided in Appendix D (mowing or burning is not necessary)
c. If a site was previously in corn/soybeans, potentially only 1-2 herbicide applications would be necessary prior to planting
2. Bioreactor has already been constructed and site vegetation is dominated by non-native cool season grasses
a. Follow option 3 or 4 from the list provided in Appendix D
In summary, thorough site preparation over multiple years is often necessary when executing a non-native cool season grass transition as this allows time to completely kill the current vegetation, time to flush and kill multiple rounds of problematic weeds, depletion of the weed seed bank and weed root stock, and the ability to address any additional vegetation issues. There is no shortcut for transitioning non-native grasslands to high quality native pollinator/monarch habitat.

APPENDIX D: SITE PREPARATION
Non-native Cool Season Grassland Site Preparation Options: Best to Worst
1. CROP – SOY, CORN, SOY
Mow summer, fall herbicide, soybeans, corn, soybeans, plant dormant

2. CROP – SOY, SOY
Mow summer, fall herbicide, soybeans, soybeans, plant dormant

3. HERBICIDES – 4 APPLICATIONS, 2 YEARS
Mow summer (*& bale), fall herbicide, (*dormant/early spring prescribed burn), 3 herbicide applications spring-fall, plant dormant
*bale or prescribed burn are residue removal options. Doing both may result in increased establishment but only one is necessary. In low residue grasslands (e.g. mowed/grazed grasslands) residue removal may not be necessary.

4. HERBICIDES – 3 APPLICATIONS, 1 YEAR
Mow and bale in late summer/fall or dormant/early spring prescribed burn, 3 herbicide applications spring-fall, plant dormant

5. HERBICIDES – 2 APPLICATIONS, ½ YEAR
Mow summer (*& bale), fall herbicide, (*dormant/early spring prescribed burn), spring herbicide, plant spring
*bale or prescribed burn are residue removal options. Doing both may result in increased establishment but only one is necessary. In low residue grasslands (e.g. mowed/grazed grasslands) residue removal may not be necessary.

6. HERBICIDES – 1 APPLICATION, ¼ YEAR FAIL – NON OPTION
Mow summer, fall herbicide, plant dormant

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The objective of this project was to develop best management practices for converting existing non-native cool season grasslands to native pollinator/monarch habitat at bioreactor sites. Plot locations were sited at farms owned by Iowa Soybean Association members and site selection was facilitated with support from Iowa Soybean Association Staff, specifically Keegan Kult. The study included seven plots, all of which were grassland transitions. The approach for site preparation and planting generally complied with USDA-NRCS requirements for establishing pollinator habitat as of spring 2016. This approach utilized half a growing season to prepare a site for planting and, at the time, was an approach consistent with NRCS practices. In 2016 existing vegetation was mowed after August 1 and then sprayed with one or two applications of glyphosate in the fall, except one site where a grass selective herbicide was sprayed followed by an application of glyphosate. Sites were planted in fall (dormant season) of 2016.

Observations over the three years indicated that a half growing season of site preparation for a non-native cool season grassland to native habitat transition is insufficient site preparation to ensure native plant establishment. Of the seven grassland transition sites in this study, one site is promising, with a high density of native forbs (wildflowers) establishing and a relatively low density of problematic weeds. Two sites have a medium density of native forbs with incomplete establishment due to weed pressure or native grass competition. The remaining four plots have poor or failed establishment. It appears the major factor limiting establishment at all seven sites is weed pressure.

RECOMMENDATIONS

There are two scenarios in which a landowner may find themselves if they wish to establish native habitat on top of a bioreactor.
1. Bioreactor is being constructed
a. Wait until construction is complete and site has been graded to level
b. Follow option 3 or 4 from the list provided in Appendix D (mowing or burning is not necessary)
c. If a site was previously in corn/soybeans, potentially only 1-2 herbicide applications would be necessary prior to planting
2. Bioreactor has already been constructed and site vegetation is dominated by non-native cool season grasses
a. Follow option 3 or 4 from the list provided in Appendix D
In summary, thorough site preparation over multiple years is often necessary when executing a non-native cool season grass transition as this allows time to completely kill the current vegetation, time to flush and kill multiple rounds of problematic weeds, depletion of the weed seed bank and weed root stock, and the ability to address any additional vegetation issues. There is no shortcut for transitioning non-native grasslands to high quality native pollinator/monarch habitat.