Getting the most out of cover crops: How timing of termination influences soil health, pest control, and improved crop production
Results were presented and discussed with approximately 530 growers, extension personnel, agricultural industry professionals, agricultural educators, and legislators from Pennsylvania at six outreach events. All second-year field data has been collected and is being analyzed; some sample processing and laboratory analysis is still needed. We added evidence to last year’s conclusion that planting green can be detrimental to stand establishment in a dry year (as in 2015), as timely 2016 spring rainfall resulted in the same or greater cash crop populations with planting green than with early termination.
We learned that timing of nitrogen application, not only sufficient nitrogen, may be important for maintaining corn yield when planting green; and in soybean, increased slug populations in late-terminated rye did not coincide with increased slug damage to plants. A spring meeting date with all concerned investigators and farmer-cooperators is being planned for February.
As a result of these activities, on over 10,000 acres, 50 farmers who use no-till and cover crops will delay cover-crop termination in spring until or close to crop planting, thereby enhancing soil conservation and health, reducing crop losses to slugs and weeds, and improving cash crop establishment and yields.
1. In summer 2015 (first summer of field research), preliminary results were presented and discussed with growers, extension personnel, and agricultural industry professionals from several northeastern states and Canada at five outreach events. Events included: Penn State Crop Management Extension Group Field Day, attended by 50 extension personnel; Southeast Agricultural Research and Extension Center Farming for Success Field Day (June 25), 200 attendees; Penn State Crop Diagnostic Clinic (July 28-29), attended by 110 farmers and ag industry professionals; Schrack Farms Field Day (September 1), attended by 50 farmers; and Cover Crops Field Day (September 23), attended by 30 farmers and consultants.
2. A 2016 spring meeting with all concerned investigators and farmer-cooperators
3. In 2016, results were presented and discussed with growers, extension personnel, agricultural industry professionals, agricultural educators, and legislators from Pennsylvania. Events included: Pennsylvania Agronomic Education Conference (January 22), attended by 110 agricultural educators; Potter County Crops Day (January 29), attended by 85 growers and extension personnel; Conewago and Chiques Watersheds Winter Farmers Meeting (February 25), attended by 60 farmers and technical service providers; Penn State Crop Diagnostic Clinic (July 21-22), attended by 115 farmers and ag industry professionals; Penn State Ag Progress Days Manure Hauler Training (August 18), attended by 46 commercial manure haulers; and Penn State Ag Council Research Tour (September 22), attended by 120 legislators and extension personnel.
4. A spring meeting date with all concerned investigators and farmer-cooperators is planned for February 2017.
Impacts and Contributions/Outcomes
While 2015 had a very dry spring and wet summer, 2016 reflected the 30-year normal, but was slightly drier in March through May. However, timely rainfall (around planting) resulted in abundant cover crop growth and good planting conditions. Summer drought, typical of the state, was pronounced in 2016, and while planting green helped conserve soil moisture during the drought, it is possible that the moisture conservation was not sufficient to overcome all associated negative effects.
Though both research center locations had several additional treatments, data was collected for pure rye termination early and at planting before the corn and soybean experiments to facilitate comparison across research stations and farmer-cooperator locations.
Corn Experiment: Weather delays, as well as reduced concern about the cover crop using up too much soil moisture, resulted in longer gaps between early terminations and planting in 2016 than 2015. Thus, with a 12-30 day delay between early termination and planting, biomass increased by 75-200%, but did not significantly increase at the Landisville site that had only 9 days delay between early termination and planting.
Soil was 7.6% , 7.8%, and 4.2% drier in the top 8 cm at planting with delayed rye termination at Landisville, Lancaster County Cooperator site, and Rock Springs, respectively; this was amplified compared to the 3-4% reduction in soil moisture at planting observed in 2015. At the Lancaster County Cooperator site, soil was 3% more moist on average later in the summer. At-planting soil moisture was not different between treatments at Landisville, Rock Springs, or the Clinton County Cooperator farm, but all three sites showed trends toward drier soil at planting and wetter soil later in the summer when rye termination was delayed (Figure 1). As in 2015, at all sites in 2016, soil temperature was between 1.0-3.6°F cooler at planting with late rye termination. The 1-1.5°F cooler temperatures persisted for the rest of the growing season at Rock Springs and the Clinton County cooperator farm and for one week at the Lancaster County cooperator farm (Figure 2). The difference between early- and late- killed treatments diminished after one week at Landisville, likely due to the minimal difference in rye biomass between early termination and termination at planting treatments.
Slugs were more prevalent in 2016 than 2015 due to greater rainfall in spring 2016. However, no clear or significant rye termination timing effects were evident. At the Clinton and Lancaster County cooperator farms, slug populations trended higher in late-terminated rye, but at the Landisville research farm, the opposite was true. At the Rock Springs research farm, slug abundance trended both higher and lower in late-terminated rye, depending on sampling date. At the Lancaster County cooperator farm, 74% of corn was damaged by slugs when rye termination was delayed compared to 27% when rye was terminated early; similarly, slug damage was 19% higher at the Clinton County cooperator farm. Slug damage was not different between termination times at either research farm.
Corn populations were not reduced by delaying rye termination timing in 2016, likely due to timely rainfall and good soil conditions at planting (Figure 3). However, the Lancaster County cooperator site saw a 10% corn grain yield reduction (Figure 4). Yields did not difference between early- and late- terminated treatments at the remaining three locations. In 2015, we hypothesized that either insufficient nitrogen fertilization (no side dress) or reduced corn populations were to blame for the yield reduction with delayed rye termination at two locations. However, the aforementioned Lancaster County cooperator site had comparable corn populations between treatments, and did apply side dress N. The yield loss, therefore, may have been caused by slug damage to corn; additional hypotheses include slowed nitrogen mineralization in late-killed rye treatment due to cooler soils, as well as reduced effectiveness of the side dress due to the summer drought. Year one (2015) results raised concerns about increased carbon to nitrogen ratio of rye and risk for nitrogen immobilization with delayed termination; so, in 2016 we initiated an experiment to test these effects; results are currently being analyzed and interpreted.
Soybean Experiment: As with the corn experiment, delay between early rye termination and soybean planting was longer in 2016 than in 2015. Rye biomass more than doubled at four sites with 20 or more days between early-termination and planting, and increased by 30% at the Landisville site, with 8 days of delay.
Similar to what we observed in 2015, soil was an average of 4.2% drier in the top 8 cm at soybean planting when rye termination was delayed at Rock Springs, Landisville, and the Clinton County cooperator farm. As hypothesized, soil was moister in the same delayed cover crop termination treatment three weeks after planting and throughout the rest of the summer at Rock Springs (Figure 5); a similar trend occurred at Landisville, but moisture conservation was only significant at one date later in the summer. Conversely, the Clinton County cooperator farm had drier soil with delayed rye termination at 4 and 8 weeks after planting; this was likely due to an incomplete rye termination at planting (Figure 6). Much of the rye cover crop continued to grow and take up moisture until the cooperator applied a post-emergence herbicide later in the season (Figure 7). Also, similar to what we observed in 2015 observations, soil was an average of 2.7°F cooler at planting across all five locations, and soil at four of five sites remained 1-3°F cooler throughout the growing season (Figure 8).
Slug populations trended higher in the late-terminated rye treatment at four of five sites, but were only significantly higher at Rock Springs at soybean planting, 1 and 3 weeks after planting. However, slug damage to soybeans at the VC (cotyledon) stage of growth was 7% and 10% lower in late-terminated rye at Rock Springs and Landisville, respectively. This supports our hypothesis that delaying cover crop termination provides habitat for beneficial predator arthropods that feed on slugs, possibly reducing slug herbivory on cash crops . Observed higher predation in late-killed rye at 1 of 3 sampling dates (and higher predation trends at the other two sampling dates) in 2015 adds evidence to this theory. To protect predatory insects, we planted seed at all locations that was not treated with neonicotinoid insecticides.
Soybean populations were either not effected or were higher with delayed rye termination timing (Figure 9). No population differences were measured between treatments at any cooperator location, rather soybean populations were 3% and 7% higher at the Rock Springs and Landisville research farms, respectively; the same locations where slug damage was 7% and 10% lower, respectively, suggesting slugs may have contributed to reducing soybean population in the early terminated rye treatments. Yield was reduced by 16% with the delayed rye termination at the Clinton County cooperator location (Figure 10). Some hypotheses to explain the yield reduction at Clinton County include: lack of stand uniformity or patchiness, perhaps caused by using a no-till drill instead of a planter to plant through a thick residue mat, or ineffective “late” herbicide (one day after planting), allowing the rye to compete with the soybeans until an additional post-emergence herbicide was sprayed in mid-July.
Conclusions: Overall, 2016 was a year farmers who practice planting green would be more likely to recommend planting green. Timely spring rainfall, greater research team familiarity with the specialized planter equipment, and management adjustments after the first year (2015) aided in good stand establishment, higher soil moisture at planting and in some locations for some time after planting;minimal negative impacts from the summer drought; and similar crop yields in all but one of the four or five locations in corn and soybean, respectively. In both 2015 and 2016, soil temperatures were cooler after late rye termination and soil tended to be drier at planting . Slug populations were also higher in 2016 than 2015 due to higher spring rainfall, in however, in 2016, in two locations slug damage to soybeans was lower and soybean populations were higher, after late terminated rye in two locations, supporting our hypothesis that late terminated rye may reduce slug herbivory, particularly when planting seed without neonicotinoid insecticides to protect predatory insects. A number of agricultural and conservation organizations are very interested in results of this project, and project members presented results at multiple meetings.
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