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Interseeding of camelina and pennycress into standing corn and soybean

(Johnson, Gesch, Lenssen, Wells, Postdoc Heather Matthees, PhD student Swetabh Patel, MS students Kyle Aasand and Nick Steffl)

The Postdoctoral Associate initially hired to help lead experiments associated with Objective 2 left the project in March 2018 to take a permanent position. A search for a postdoctoral replacement was immediately initiated and a new hire (Dr. Yesuf Mohammed) was brought onboard to the project 10 December 2018.


Data collection for the replicated experiment on cover crop interseeding and establishment in standing corn and soybean including all plant and soil sampling was completed at all four sites (i.e., Ames, IA; Rosemount, MN; Morris, MN; and Prosper, ND). Statistical analysis of the establishment data has been completed and a manuscript on this subject is nearly completed and will be submitted for publication by 1 March 2019. In summary, significant differences developed across locations. Generally, establishment was better at all locations in standing soybean than corn, most likely due to less competition for light and moisture in the soybean system. Winter rye tended to give better establishment than the winter oilseeds, possibly due to better tolerance to competition. Earlier establishment of covers in Minnesota and North Dakota led to better stands and cover, whereas in later interseeding into standing crop gave better results in Iowa (most southern site). Data from 2018 confirmed previous results that interseeding of covers during late reproductive phase of both corn and soybean had no significant effect on grain yield.

Seed yields of field pennycress and winter camelina interseeded into standing crop during late summer/early fall did have an impact on their subsequent yields the following spring. Generally, seed yields were 50% or less at all locations than what we have previously demonstrated when they were direct-seeded after harvest of short-season grain crops like spring wheat. Also, interseeding appeared to negatively impact oil concentration.


Similar to the previous season, relayed soybean yield was greater after corn than soybean. Generally, the herbicide-killed rye had little or no effect on soybean yield, whereas field pennycress and camelina decreased yield of relayed-soybean yield, but the yield reduction tended to be less in the corn than the soybean system. In the soybean system (i.e., covers interseeded into standing soybean the year prior to relaying soybean), yield for soybean relayed into field pennycress and camelina were reduced by as much as 30% when compared with the control (i.e., soybean planted into plots left fallow over the winter).

Plots used for the first experiment, initiated in 2016 and relay-cropped with soybean in 2017, were planted to grain corn in 2018 to determine treatment effects on yield and grain quality. All sites collected yield data and sent seed samples to Morris, MN for analysis. However, analyses have not been completed at this time. 


Experimental sites

Field experiments to establish cover crops into standing corn and soybean were repeated (second experimental series) at Prosper, ND, Morris and Rosemount MN, and Ames, IA in 2017. Four replicated blocks of corn and soybean were planted at each site and soil and crop managementwerefollowed in accordance to locally adapted best management practices. Weeds and insects were controlled according to need within each site.


Fall cover crop establishment

Cover crops were planted between late August to mid-September into corn and soybean at three planting dates (PD) which corresponded with corn and soybean development. The first PD was during the corn R4 and soybean R6 growth stage, PD2 corresponded to the corn R5 and soybean R7 growth stage, while PD3 corresponded to the corn R6 and soybean R8 growth stage. Camelina and pennycress were seeded at 15 kg ha-1, while winter rye was seeded at 75 kg ha-1. One control plot in which cover crops were not seeded was included within each block. At Ames andProsper seeds were broadcast between the corn and soybean rows by hand followed by a light raking. At the Morris and Rosemount sites, cover crops were seeded with a Lee Avenger high clearance tractor modified to broadcast seed with light incorporation.

In the fall, prior to freeze-up, cover crops were assessed for establishment success using several metrics. First, cover crop stand counts were completed by averaging the number of individual plants in a 0.09 m2 area collected from the center row at two locations within each plot. Aboveground cover crop biomass was determined by sampling plants from a 0.09 m2 area adjacent to that used for stand counts. Finally, cover crop establishment was assessed using the percentage of green cover produced by the growing cover within each plot by processing two photos using theCanopeo application.

Corn and soybean were harvested similarly at all locations in October. For the corn, as much of the stover was removed from the plots, either through adjusting the combine settings or through using a forage harvester after grain combine samples were collected. Corn and soybean yields were adjusted to 15.5 and 13% moisture respectively.


Winter oilseed effects on relay-cropped soybean

To determine the effects of winter camelina and pennycress on relay cropped soybean, plotsinterseededwith these species in the fall of 2016 in Ames, Morris, and Prosper were utilized. The winter survival of the cover crops in this cash cover crop-relay soybean system is important for maximizing oilseed cover crop yields. Therefore, to assesswintersurvival of the cover crops, stand counts, cover crop biomass, and percent green cover were collected in April 2017. The percent winter survival was calculated bypaireddifference of fall stand counts and spring stand counts. 


Soybean was relay planted into standing winter camelina and field pennycress in May 2017 at all sites using a no-till drill in Morris and with a 4-row planter equipped with Kinze boxes and openers equipped with trash wickers in Ames, IA. Soybean planting time coincided with the bolting stage of winter camelina and field pennycress in Morris, although in Iowa field pennycress bolted well before it was safe to plant soybean. One week prior to planting soybean, the winter rye cover crop was terminated with glyphosate. Camelina and field pennycress were harvested at maturity with a plot combine with the sickle bar cutter set above the height of the top of the growing soybeans. Yield samples weredried,and cleaned for final yield analysis after adjusting data toa seedmoisture of 10%. Seed oil and crude protein concentrations were determined for camelina and field pennycress using pulsed NMR. Relay cropped soybean was harvested at maturity with a plot combine in October of 2017. Seed samples were cleaned before weighing for yield determination; yield results are presented at 13% moisture.



Establishing winter annual cover crops in standing corn and soybean

The final results from data collected over two growing seasons from seven locationsindicatesthat a distinct latitudinal gradient exists for optimum times tointerseedwinter annual cover crops into standing corn and soybean. Greater establishment success was achieved with all winter annual cover crops in this study at more northerly locations (Prosper and Morris) with less establishment observed in Ames. Establishing winter annual cover crops in standing corn was more difficult, and greater success was achieved by establishment into standing soybean.


When interseedinginto standing corn in the fall across both years, the green cover was greatest at the Morris location, while across all sites and planting dates, winter rye had double the amount of green cover (14.5%) than both field pennycress (5.77%) and winter camelina (5.53%) (Fig. 6). Additionally, winter rye had the greatest establishment in Morris, with an average of 211 plants m-2 across all planting dates, while both field pennycress (653 plants m-2 in Prosper) and winter camelina had greater stand establishment in the more northerly sites (286 and 297 plants m-2 in Prosper and Morris, respectively). Across locations, there was a latitudinal gradient for the optimum time to interseed the winter annual cover crops into standing corn. For example, field pennycress had the greatest green cover in the fall when planted during the R5 (12.0%) stage in Ames, the most southern site, while at Prosper, the most northern site, its establishment and green cover were greatest when planted during the R4 stage (8.3%). Like field pennycress, the more northern sites had better fall establishment of winter camelina with early to mid-planting dates, while in Ames, establishment improved with later planting dates. Establishment and green cover of winter rye were always greatest when seeded during the R5 stage at all sites, except Rosemount, where 5% greater green cover was achieved when seeded at the R4 stage. Interseeding winter annual cover crops into standing corn did not result in yield declines at any location or planting date. Overall, yields ranged from an average of 12.0 Mg ha-1 in Morris, to 15.1 Mg ha-1 in Rosemount.

When interseedinginto standing soybean in the fall across both years, the percent green cover of field pennycress was greatest at Morris and Prosper (14.9 and 16.1%, respectively) and was lowest in Ames, IA (4.8%) (Fig. 7). Winter camelina fall green cover was nearly 25% in Morris which was almost double that of all the other sites. Winter rye green cover in the fall was also greatest in Morris (30%) and in Amesit established better than camelina and field pennycress. Overall, when interseedinginto standing soybean, field pennycress had the greatest fall stand establishment (343 plants m-2) whereas establishment rates for rye (142 plants m-2) and winter camelina (176 plants m-2) were similar across sites. As described for establishing cover crops in standing corn, field pennycress and camelina had the greatest number of plants established in the fall per square meter at the more northerly sites (Prosper and Morris). Overall, soybean yields differed based on location.  Soybean yields were greatest in Ames (3.9 Mg ha-1) and lowest in Rosemount (2.9 Mg ha-1), but yields were not impacted byinterseeding of cover crops.

Competition for both light and moisture as well as climate differences likely affectedestablishmentof winter annual cover crops in standing corn the most. In Ames, the established covers may have sustained more shade stress because of a longer growing season for the corn and soybean varieties used, and thus, later harvest of them. Because of this, the cover crops were shaded for a longer periodunder standingcorn and soybean than they were at the further north sites where physiological maturity was reached earlier, and thus, they were harvested earlier. Therefore, oilseeds planted into corn earlier in Ames face greater competition for resources as compared with the oilseeds planted earlier in more northerly locations where physiological maturity is reached earlier along with an accumulation of fewer growing degree days as freeze up approaches. Competition for light and moisture in soybean is presumed to be less than in corn as soybean typically reach physiological maturity earlier than corn at all locations in this study. Additionally, as soybean plants mature, the leaves are dropped from the plant thereby opening the canopy and reducing light competition. This is likely why there was overall slightly better establishment and greater green cover achieved wheninterseedingwinter annual cover crops into standing soybean than corn.

Results indicate that wheninterseedingwinter annual oilseeds in more northerly locations (North Dakota through central Minnesota), optimum times to maximize field pennycress and camelina establishment is during the corn R4 and R5 growth stages. However, in more southerly locations (southern Minnesota through Iowa) later planting dates (R6 or even after harvest) will maximize winter annual oilseed establishment. Wheninterseedinginto soybean, planting at the R7 stage resulted in greatest field pennycress establishment whereas seeding at the R8 stage resulted ingreaterestablishment of winter camelina, regardless of site. Similar stand establishment was observed for rye and winter camelina when seeding into the two standing crops at all sites.


Oilseed yields and quality

The first-year results (i.e., 2017) indicate that when seeded into corn, both field pennycress and winter camelina yields increased with later planting dates at Ames to a high of nearly 600 and 400 kg ha-1, respectively, whereas field pennycress yields were greatest when seeded at the corn R4 stage in Morris (nearly 650 kg ha-1) and decreased with later planting dates (Fig. 8). Winter camelina yields when seeded into corn were greatest in Morris at the R5 and R6 stages, which averaged 436 kg ha-1. Similar trends were observed at each site when field pennycress and winter camelina were seeded into soybean. In Ames, greater yields for both oilseeds were achieved with later planting dates, while later planting dates improved winter camelina yields in Morris. However, field pennycress yields were decreased with later planting dates in Morris wheninterseeded into soybean. Overall, field pennycress outperformed winter camelina in yield at both sites, but yields of both field pennycress and winter camelina were lower than expected. There was stand loss of winter camelina between flowering and maturity, which we believe can be attributed to growing conditions and a potential insect infestation. In Waseca, MN,the both oilseeds did not survive to harvest due to weather conditions (i.e. excess moisture and hail). Oilseed yields from Prosper were not included in this analysis as the samples were still being processed as the report was being prepared.


The oil content of both field pennycress and camelina was lower than normally observed when interseededinto corn and soybean. Overall, when seeded into corn, oilcontent of both field pennycress and winter camelina was greater in Morris than Ames (329 and 296 g kg-1). Later planting dates maximized oil content of both field pennycress and winter camelina when interseeded into both corn (31 and 37 g kg-1, respectively) and soybean (31 and 32 g kg-1, respectively). In Morris, later planting dates maximized winter camelina oil  content in both corn (37 g kg-1) and soybean (35 g kg-1), but field pennycress oil content was maximized with earlier planting dates in both corn (31 g kg-1) and soybean (32 g kg-1).

Winter annual cover crop effects on relay cropped soybean

Overall, total grain yield in the system which considers both oilseed and soybean yields was impacted when cover crops were seeded into standing corn in Ames the previous growing season, but not when interseededinto soybean at either location (Fig. 9). In Ames, when field pennycress was interseededinto standing corn, the result of competition for space, light, and water reduced total grain yield by nearly 700 kg ha-1, while winter camelina reduced total grain yield by over 1200 kg ha-1 compared with the control no cover crop treatment.  Differences in total grain yield when cover crops were interseeded into soybean were only based on location differences with Ames out yielding Morris by nearly 500 kg ha-1. Relay cropped soybean yields are still being calculated for the Prosper site; the Waseca site was abandoned due to climatic conditions and failure of the cover crops.

An experiment was esatablished in Prosper, ND in May 2016 to evaluate optimizing planting date for seeding winter camelina, pennycress, and winter rye into standing corn and soybean. Soil samples were taken prior to planting and after harvesting soybean and corn. These samples were analyzed for soil moisture and macronutrient (i.e., N, P, & K) content. Corn and soybean were planted according to best management practices for that site with regard to tillage and seedbed prep, cultivar maturity, fertilizer application, and pest control. Planting was in May and harvest in September for soybean and in October in corn.
Cover crops including winter camelina, pennycress, and winter rye were interseeded into standing corn at
all four sites at three different planting times which corresponded to the R4, R5, and R6 growth stages of
development and interseeded into soybean at R6, R7, and R8 stage of crop development. At Prosper, ND
the covers were broadcast seeded between crop rows by hand and incorporated with a garden rake. In the fall just before soil freeze up, final stand counts and biomass samples of the interseeded cover crops were taken in duplicate from each plot. Biomass samples were dried to determine dry matter yield on an area basis.
At the Prosper site, pennycress populations were greatest when interseeded into standing corn at the first and second dates (R4 and R5) and lowest when seeded at the last date (R6). Winter camelina plant populations were greatest when seeded at the last date into standing corn. Winter rye plant populations when interseeded into corn and soybean at Prosper remained constant across planting dates, but tended to be lower than camelina or pennycress. Similar to interseeding into standing corn, winter camelina interseeded into standing soybean at Prosper had the greatest plant populations at the latest planting (R8) and lowest populations when seeded at the first date (R6). Pennycress plant populations remained relatively constant at Prosper when seeded across all soybean growth stages. When seeding into
standing corn at the second date, winter rye had the greatest biomass accumulation (41 kg ha-1), followed closely by winter camelina planted at the same time (31 kg ha-1). The third planting date into standing corn at Prosper produced poor biomass, ranging from 4 to 14 kg ha-1 across species. Overall, greater average biomass was accumulated across all cover crop species and planting dates when interseeded into soybean (84 kg ha-1) than into corn (18 kg ha-1). Winter rye produced between 121 and 146 kg ha-1 of biomass when planted at the first and second dates into soybean. Pennycress also produced appreciable biomass when seeded during the first and second dates (93 to 133 kg ha-1), but less than 22 kg ha-1 of biomass was produced when seeded at the last date. Winter camelina also followed a similar trend to pennycress when interseeded into soybean at Prosper (Fig. 18)
Successful cover crop establishment can reduce erosion. Therefore, estimates of percent green cover taken in the fall and spring can help make decisions on the best time to interseed these cover crops in order to maximize erosion protection. Winter camelina, when seeded into corn reached a maximum of roughly 15% cover when seeded at the second date, but was much more successful in covering the soil when seeded into soybean regardless of growth stage, as winter camelina averaged between 40 to 50% soil coverage. Establishing a suitable soil cover using interseeded winter cover crops was more challenging in corn than soybean. Seeding during all corn growth stages resulted in a range of 2 to 15% green cover for winter rye, pennycress, and winter camelina (Fig. 6a). However, establishing soil cover when seeded into standing soybean provided better results. Winter rye averaged between 20 and 31% coverage with greater ground cover when seeded earlier. Pennycress provided 45% green cover when seeded into soybean at the
first date and declined to under 20% cover when seeded at the last date. Winter camelina provided the greatest (35%) green cover when seeded at the second date in soybean, and was lower when seeded earlier or later in soybean development. There was generally not much difference among the three cover crop species with regard to amount of cover provided in both the corn and soybean systems.Our initial (1st year) results indicate that establishing winter annual cover crops into standing corn generally is a greater challenge than establishment in soybean. This is most likely due to light interception and suitable soil moisture for germination and growth.
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