Developing Corn Silage Systems to Meet the Needs of Cover Crops

2018 University Research Station Trials

Effect of corn architecture and population- Borderview Research Farm in Alburgh, VT

Impact of Population

Corn population impacted corn yield and cover crop ground cover. Corn yields ranged from 14.1 to 17.9 tons ac^-1 (Figure 2 ) but were not statistically different from one another. Yields generally increased with increasing seeding rate until 32,000 seeds ac^-1 after which yields declined slightly. Ground cover followed the opposite trend decreasing as populations increased.

Cover crop ground cover is one indicator of cover crop establishment success as the better the cover crop establishes and fills in, the less bare ground should be exposed through its canopy. We hypothesized that lower light availability under dense corn canopies will reduce cover crop establishment success and would therefore be reflected in lower ground cover. However, the populations allowed similar amounts of light to infiltrate the canopy throughout the season (Figure 3). Despite slightly lower light availability within the relatively high yielding corn crop at the 32,000 seeds ac^-1 treatment, the cover crop was still able to maintain over 30% ground cover post-harvest.

When corn hybrids were separated by relative maturity, corn seeding rate significantly impacted cover crop ground cover for long season hybrids (Figure 4 ). The two highest seeding rates resulted in cover crop ground cover levels below 30% whereas the other seeding rates all supported >35% ground cover.

In general, the canopy closed within two weeks of the cover crop being interseeded at which point PAR infiltration was reduced to by 65-80%. The sharp growth of the corn canopy and subsequent decline in light availability was likely attributed to a 0.70” rain event on 17-Jul, the first substantial rainfall in 11 days. The amount of time until canopy closure was likely influenced by these dry conditions and may differ in other years. This period of drought also coincided with the interseeding of the cover crop and likely slowed its emergence. This situation exemplifies the challenge with managing interseeded cover crops in this region.

Impact of Ear Type

Corn hybrids are typically characterized as “flex”, “semi-flex”, or “fixed” ear types. Flex ear hybrids are more cost effective when planted at lower seeding rates as they have the ability to adjust corn ear size relative to plant population to remain high yielding despite fewer plants. Fixed ear types, on the other hand, have been bred to remain consistent in ear size regardless of plant population and are therefore become more profitable as populations are increased. These hybrid types also tend to differ in plant architecture or growth habit. Fixed ear hybrids tend to have a more upright leaf structure as they are better suited to the compact nature of high seeding rates. Therefore, we hypothesized that ear type would impact the corn population that would support a high yielding corn crop and successful interseeded cover crop. We found that ear type did not significantly impact corn yield across populations (Figure 5 ).

Although we did see a divergence of about 2 tons ac^-1 in the fixed ear hybrid yields above 32,000 seeds ac^-1, we did not observe a difference at low populations (Figure 6). Furthermore, in terms of cover crop ground cover, the opposite trend was observed than expected with the fixed ear hybrid plots outperforming flex ear hybrid plots, in terms of cover crop ground cover, at low populations while the opposite occurs at higher populations. None of these differences were statistically significant.

Impact of Hybrid Relative Maturity

Corn hybrids are also characterized by the length of the growing season required for the hybrid to reach physiological maturity. Long season corn varieties, or those with higher relative maturities, are generally regarded as having higher yield potentials as they are able to maximize resources over the longer growing period. This trend was observed in this trial as the long season hybrids produced yields approximately 3 tons ac^-1 higher than season hybrids (Figure 7 ). However, in northern regions where the growing season is relatively short and is often shortened further due to unfavorable weather, short season varieties are being promoted as potential tools to be more resilient to unpredictable weather. These varieties likely have faster growth rates than longer season varieties as they are bred to mature in shorter periods of time. The short season hybrids did reach significantly lower dry matter contents at harvest compared to long season hybrids, with the short season reaching 36.4% and the long reaching 39.0%. In this trial, however, light infiltration remained higher for longer in short season variety plots (Figure 8 ).

Light infiltration was approximately 10% higher in short season plots two weeks after corn was planted and approximately 20% higher after three weeks. As mentioned previously, the cover crop was interseeded on 12-Jul but rainfall was not experienced until 17-Jul. The cover crop therefore likely only had about 10 days to germinate and establish before the corn canopy significantly reduced the available light. Unfortunately, we were unable to collect cover crop ground cover data from the short season varieties to see whether cover crops established better where yields were lower.

Corn quality also differed slightly across relative maturities (Table 17). Crude protein (CP) was slightly higher in short season varieties but long season varieties had lower acid detergent fiber (ADF) and higher starch. Due to the significant difference in yields, milk per acre was higher in long season varieties. All other measures did not differ statistically between relative maturity groups.

Table 17. Corn quality by relative maturity, Borderview Farm, VT.

Treatments in bold were the top performer for that category.

‡LSD; least significant difference at the p=0.10 level.

NS- not statistically significant.

Timing Trial- Impact of Cover Crop Interseed Timing, Borderview Farm, Alburgh, VT

Deciding when to interseed a cover crop is challenging. On one hand you want to allow the cover crop time to establish before the corn blocks the light, but on the other hand, you don’t want the cover crop to compete with the establishing corn for resources. Generally, corn can be interseeded anywhere from the V2 to V6 growth stage. After V6, most interseeding equipment is not tall enough, increasing the risk of damaging the corn crop. In this trial, as interseeding was delayed to the V6 growth stage, cover crop success, indicated by post-harvest ground cover, decreased (Figure 9). However, ground cover was <50% for all interseed timing treatments. Corn yields were not significantly impacted by timing of interseeding. In addition, corn quality was not impacted by timing of interseeding (Table 18). 

  Table 18. Corn quality by interseed timing, Borderview Farm, VT.

Treatments in bold were the top performer for that category.

‡LSD; least significant difference at the p=0.10 level.

NS- not statistically significant.

Light available at the time of interseeding varied dramatically across the timing treatments (Figure 10). The arrows indicate the date the corn was interseeded corresponding to the V2, V4, and V6 growth stages. At the V2 and V4 growth stages virtually none of the PAR was being obstructed by the corn canopy. However, by the time the corn reached the V6 stage, the canopy was already obstructing almost 70% of the light. That was reduced by an additional 20% by the following week where the level remained for much of the season. However, this did not appear to significantly impact cover crop establishment as post-harvest ground cover was approximately similar to that of the V4 seeded cover crop which had an additional few weeks to grow. However, it is also important to note that following the V2 and V4 interseedings, no rainfall was experienced for 12 days. Therefore, the cover crop may have not germinated as quickly, reducing the impact between the interseed timings.

Impact of Corn Ear Type

With fixed ear hybrids having generally a more upright leaf structure, we would expect better cover cropping success with a fixed ear hybrid over a flex ear hybrid. In this trial, we observed the highest cover crop success, indicated by post-harvest ground cover, from the fixed ear hybrids, however, this was only observed when interseeded at the V2 growth stage and was not statistically significant (Figure 11). Corn yield and quality parameters also did not differ across the ear types.

2018 On-Farm Trials

Effect of corn architecture, seeding rate, and hybrid 

 Corn Populations and Yield - Machia Farm, VT  

Plant populations in the lower seeding rate treatment were 3,000 plants ac^-1 below the seeding rate and the plant populations in the higher seeding rate were 3,600 plants ac^-1 below the seeding rate (Table 19).  However, this variation in plant population, regardless of hybrid or seeding rate did not significantly impact the yields. Yields ranged between 26.2 and 27.8 tons ac^-1. Hybrid selection prove to have a bigger impact on yields with the flex ear variety yielding on average 1 ton per acre higher than the fix ear variety. 

Table 19. The impact of seeding rate and hybrid on corn silage yield, Machia Farm, VT. 

The top performer for a category is highlighted in bold.

Cover crop germination was not uniform in mid-October. To more accurately capture cover crop establishment success, cover crop and weed populations were counted using the beaded string method, as opposed to randomly selecting locations to sample for biomass. On 17-Oct, populations were counted on five 10-foot lengths in each of the 24 plots.

Cover crop coverage was 14% greater in the lower seeding rate than the higher seeding rate (Table 20). This may be due to less competition for sun, moisture, and soil nutrients.  There was an equal amount of weeds at either rate.  There was an 8% higher cover crop establishment success in flex ear plots than fix ear plots.  Cover crop coverage was highest (38%) in the fixed ear with low seeding rate treatments. 

Table 20. Impact of corn population and variety on cover crop establishment, Machia Farm, VT.

The top performer for a category is highlighted in bold.

Effect of corn architecture, seeding rate, and hybrid - Smith Farm

Overall, yields were most impacted by corn population (Table 21).  Late planting, heavy clay soil and dry weather combined for a low overall yield average of all plots of 13.9 tons acre^-1.  At the higher seeding rates yields were 0.7 tons acre^-1 higher with the fix ear variety.  At the lower seeding rate, yields were 0.6 tons acre^-1 higher with the flex ear variety.

Table 21. Impact of corn variety and population on corn silage yield, Smith Farm, VT.

The top performer for a category is highlighted in bold.

± collected on 31-Jul, measured using 3 x 1/1000^th acre population counts in each plot

^Π collected on 12-Oct, measured by counting plants harvested using 1 x 1/1000^th acre sample in each plot

Cover Crop Populations
Cover crop germination was fairly uniform, other than where there was heavier weed pressure in specific areas in individual plots (Image-1-Interseeding-Cover-Crops). All three species (annual ryegrass, radish, red clover) were observed to have germinated.  However, the red clover seemed to be the least successful overall.  Cover crop establishment was quantified during the corn growing season by using the Canopeo ‘fractional green canopy cover’ measurement using a smartphone app roughly every two weeks up until harvest.  Post-harvest weather quickly turned snowy and we were unable to capture a post-harvest measurement using this method.  To align with the other sites, we collected percent cover using the beaded string method, as opposed to randomly selecting locations to sample for biomass for our final measurement. On 20-Dec, populations were counted on three 10-foot lengths in each of the 24 plots.  Because of previous cold weather, weeds were not counted, and total cover generally went down as much of the cover crop had gone dormant and/or been winter-killed (radish).  However, dead cover crop residue was quantified at this sample date.

Overall, the Flex ear variety consistently had more cover throughout the season the than Fix ear variety (Table 22).  Early in the season, there was higher percent cover in the higher seeding rate treatments, with some catch up of cover crop in the lower seeding rate before harvest.  However, at the end of the season, there was negligible difference among corn seeding rate treatments of percent cover crop cover.

Table 22. Impact of plant population and variety on cover crop establishment, Smith Farm, VT.

The top performer for a category is highlighted in bold.

^Π measured using Canopeo digital fractional green canopy cover measurement

± measured using beaded string method

2018 Maine On-Farm Trial Results

The timing trials at the ME sited consisted of four overseeding dates at approximately weekly intervals, starting 6/24.  Only the cover crop planted at the first seeding date (6/24, at V4) was successful.  We considered the following reasons for the failure of later seedings:

1. Herbicides with low residual activity were used.  Even so, injury can sometimes occur.  However, since the initial seeding was successful, herbicide injury does not seem a likely cause. 
2. Within four days of the first seeding, 0.71” of rain fell.  Within five days of the second seeding, 0.43” of rain fell.  Insufficient moisture would not seem to be a likely cause, given this rainfall. 
3. We know, of course, that the amount of light penetrating the crop canopy will decline as the corn crop grows.   At the time of the first overseeding, 98% of the ambient light reached the ground between the corn rows.  By the second overseeding date one week later, only 62% of the light reached the ground.   By the third overseeding date (two weeks after the first), only 36% of light reached the ground between the corn rows.  Although we cannot be certain, we suspect that insufficient light was the reason for the failure of later interseedings.

The timing trial and the flex/semi-flex trial at the Barker Farm were the two trials with measurable cover crop after harvest.  Cover crop yield ranged from 1650 lbs dry matter per acre to 371 lbs dry matter per acre.  In all plots, the brassicas dominated the stand.  This was a particular concern to one cooperating farmer, who observed that the brassicas created slippery driving conditions for trucks during the silage harvest.  It also means that there would be few living plants the following spring, since the brassicas are not winter-hardy.  

2019 University Research Station Trials 

Effect of corn architecture and population- Borderview Research Farm in Alburgh, VT

The results from 2018 and 2019 were analyzed together to get a sense of how the treatments performed by each year and across the two years of the

Interactions

There were no statistically significant interactions between the main effects of corn population and corn ear type (Table 23). This indicates that corn varieties of different ear types responded similarly in terms of yield and quality parameters when planted at different populations.

Table 23. Interactions between the main effects of corn population and corn ear type, Borderview Farm, VT.

Significant at the * 0.1 < p > 0.05; ** 0.05 < p > 0.01; *** p < 0.01

NS- Not statistically significant

Impact of Year

The two years of the trial performed differently in terms of corn yield and quality characteristics (Table 24). Yield varied dramatically between the two trial years with 2018 yields being almost 9 tons ac^-1 higher than 2019. Crude protein (CP) differed by almost 1% as well. These were likely due to lower water and therefore nutrient availability in 2019 compared to 2018. The hot and dry weather also appears to have resulted in higher lignin content as the NDF digestibility (dndf) was considerably lower in 2019. Because of these yield and quality differences, 2018 would have produced more milk yield both on a per acre and per ton basis.

Table 24. The impact of year on the corn silage yield and quality by year, Borderview Farm, VT.

Statistically significant at the * 0.1 < p > 0.05; ** 0.05 < p > 0.01; *** p < 0.01

NS- Not statistically significant

Impact of Population

Corn population significantly impacted yield (Figure 12). Statistically, no additional yield benefit was gained by attaining a plant population higher than 30,000 plants ac^-1. Population did not impact corn silage quality.

By two weeks after cover crop interseeding, the corn canopy had significantly closed reducing 65-70% of the potential light infiltrating to the ground (Figure 13). Therefore, the newly planted cover crop had approximately 2-3 weeks from the time of seeding to germinate and establish prior to full canopy closure, in which very little light penetrated to the ground level for the remainder of the season. This demonstrates the challenge interseeding presents as any delay in seed germination or establishment (i.e. limited moisture, low vigor, etc.) significantly reduces the time available to the cover crop to properly establish increasing the chance of survival through the rest of the growing season.

Due to complications in the 2018 growing season, cover crop measures were not captured post corn silage harvest. However, these data are available for the 2019 growing season but were not statistically analyzed. Overall, ground cover from interseeded cover crops post corn silage harvest were very low averaging 4.69% with no obvious differences between populations. This will continue to be studied in the coming year.

Impact of Ear Type

Corn hybrids are typically characterized as “flex”, “semi-flex”, or “fixed” ear types. Flex ear hybrids are more cost effective when planted at lower seeding rates as they have the ability to adjust corn ear size relative to plant population to remain high yielding despite fewer plants. Fixed ear types, on the other hand, have been bred to remain consistent in ear size regardless of plant population and are therefore more profitable as populations are increased. These hybrid types also tend to differ in plant architecture or growth habit. Fixed ear hybrids tend to have a more upright leaf structure as they are better suited to the compact nature of high seeding rates. Therefore, we hypothesized that ear type would impact the corn population that would support a high yielding corn crop and successful interseeded cover crop.

Little difference in light infiltration was observed between corn ear types (Figure 14). Fixed ear varieties limited light infiltration slightly more than flex ear varieties, however, by 36 days after interseeding both had reduced light infiltration by approximately 90% and remained similar for the remainder of the trial. Overall, the ear type did not appear to significantly impact light infiltration through the corn canopy.

Corn ear type did not significantly impact yield and had a minor impact on corn silage quality parameters (Table 25). Crude protein was approximately 0.3% higher in flex ear varieties than the fixed ear varieties. This is to be expected as these varieties can change the size of ears formed depending on resources available (i.e. populations) which impacts the nutrient concentration in the end silage sample. However, the only other quality parameter that was significantly impacted by ear type was NDF digestibility at 30 hours. Again this was higher in flex ear varieties which we’d expect as there is likely a higher proportion of ear material compared to the less digestible fiber materials.

Table 25. The impact of corn ear type on silage yield and quality, Borderview Farm, VT. 

Significant at the * 0.1 < p > 0.05; *** p < 0.01

NS- Not statistically significant

In both years, cover crop establishment was poor and was difficult to obtain measurements on the minimal and spotty growth. Ground cover measurements could only be captured in some plots post corn harvest. Regardless of the treatment there was less than 5% ground cover provided by the cover crop in late-Oct.  More data will be collected in the coming year to better understand these implications.

Timing Trial- Impact of Cover Crop Interseed Timing, Corn Maturity, and Corn Ear Type at Borderview Farm, Alburgh, VT

Due to weed pressure limiting cover crop success in the trial area in 2019, cover crop establishment data were only available for 2018 and therefore, only data for that year are presented below.

2019 On-Farm Trials

Effect of corn architecture, seeding rate, and hybrid – Machia Farm, VT

Corn Populations and Yield

Plant populations in the lower seeding rate treatment were an average 4,083 plants ac^-1 below the seeding rate and the plant populations in the higher seeding rate were an average of 5,167 plants ac^-1 below the seeding rate. Plant populations were correlated with yield (i.e. the higher planting population had higher yields), regardless of variety. 

Yields ranged between 16.3 and 18.6 tons ac^-1. The variety TMF2Q419 variety had the highest yield.  On average, TMF2Q419 variety had 0.8 tons ac^-1 more than the TMF2L395 variety. The highest seeding rates had the highest yields (Table 26).

Table 26. Impact of plant populations and variety on corn silage yields at the Machia Farm, VT.

The top performer for a category is highlighted in bold.

Cover Crop and Weed Populations

Cover crop germination was not uniform in early November. To more accurately capture cover crop establishment success, cover crop and weed populations were counted using the beaded string method, as opposed to randomly selecting locations to sample for biomass. On 4-Nov, populations were counted on five 10-foot lengths in each of the 24 plots.

Overall, cover crop populations were very low, covering between 10-13% of the field (Table 27). There were negligible or no differences in cover crop populations between the lower and higher corn seeding rate, and corn variety. Of the cover crop present, 76% was ryegrass, 24% radish, and 0% clover established. Percent cover of weeds averaged at 0% regardless of seeding rate, or corn variety. What few weeds were present were predominantly barnyard grass.

Table 27. Impact of seeding rate and corn variety on cover crop establishment at Machia Farm, VT. 

The top performer for a category is highlighted in bold.

Effect of corn architecture, seeding rate, and hybrid – Foster Farm, VT

Table 29 below shows the average yields at the different plant populations for each of the other variables. We did observe the expected trend of increasing yield with increasing population for fixed ear, vertical-leaf architecture varieties. Similarly, for flex ear, horizontal-leaf architecture varieties, we saw slightly higher yields at lower populations but the trend was less clear than with the fixed ear varieties. We also saw some difference between long and short season varieties with the long season varieties outperforming the short season varieties by an average of 0.8 tons^-1. At populations above 32,000 plants ac^-1, the fixed ear varieties outperformed the flex ear varieties by approximately 2-3 tons ac^-1. At lower populations there was little difference between the two ear types.

Table 29. Impact of corn population on yields of corn varieties with different ear type and maturities at Foster Farm, VT.

The top performer for a category is highlighted in bold.

Effect of corn seeding rate on cover crop growth - Leeds Farm, ME

 A wet spring resulted in extremely late planting and the growing season was very compressed.  By the time a suitable waiting period passed after herbicide application, there was only time for one overseeding before the corn was too tall (>6’ tall) for the equipment. With only one overseeding date and no comparisons to be made, yield data was not collected on this plot in 2019.  After harvest, no significant cover crop could be found in the plot. 

 Effect of corn hybrid on cover crop growth - Misty Meadow Farm, ME

 Cover crop emergence was limited and spotty under the canopy. There was little cover visible after harvest.  It is worth noting that one side of the field was chopped in mid-August in advance of the Farm Days event.  Where the corn was removed early, there was a substantial cover crop stand come fall.    

2020 Research Station Trials

Effect of corn architecture and population- Borderview Research Farm in Alburgh, VT

Interactions

There was only one significant interaction between main effects (Table 30). A significant interaction between corn population and variety for cover crop dry matter yield indicates that the cover crop produced differing amounts of biomass when interseeded into the same corn variety planted at different populations. Figure 15 displays these differences. For most varieties, a lower seeding rate resulted in higher cover crop biomass; however, 38N85, 9070AM, and SW4010 did not follow this trend. These three varieties had similar or higher cover crop biomass when corn populations were higher. This may be due to plant architecture.  The lack of other significant interactions indicates that corn varieties responded similarly in terms of yield and quality parameters when planted at different populations.

Table 30. Significance of the main effects and main effect interactions, Borderview Farm, VT.

Significant at * 0.1 < p > 0.05; ** 0.05 < p > 0.01; *** p < 0.01

NS- Not statistically significant

Impact of Population

Corn population significantly impacted yield (Figure 16). Corn yields were significantly lower when populations of 28,000 and 34,000 plants ac^-1 were used compared to 38,000. However, no additional yield benefit was observed from increasing from 28,000 to 34,000 plants ac^-1. Population did not impact corn silage quality.

By two weeks after cover crop interseeding, the corn canopy had significantly closed reducing approximately 80% of the potential light infiltrating to the ground (Figure 17). Therefore, the newly planted cover crop had approximately 2-3 weeks from the time of seeding to germinate and establish prior to full canopy closure, in which very little light penetrated to the ground level for the remainder of the season. This demonstrates the challenge interseeding presents as any delay in seed germination or establishment (i.e. limited moisture, low vigor, etc.) significantly reduces the time available to the cover crop to properly establish increasing the chance of survival through the rest of the growing season.

Cover crop establishment also differed significantly by population (Table 31). Cover crops produced higher ground cover and biomass when interseeded into lower corn population stands. Ground cover significantly increased from 23.7% to 42% when populations were reduced below 34,000 plants ac^-1. However, ground cover was not further impacted when populations increased from 34,000 to 38,000 plants ac^-1. Similarly, cover crops produced over 300 lbs ac^-1 more biomass when interseeded into corn at 28,000 plants ac^-1 compared to corn at 34,000 plants ac^-1. Cover crop biomass was not further impacted when populations were increased from 34,000 to 38,000 plants ac^-1.

Table 31. Cover crop characteristics by corn silage population, Borderview Farm, VT.

†Treatments that share a letter performed statistically similarly to one another.

‡LSD; least significant difference at the p=0.10 level.

Impact of variety

Variety significantly impacted corn yield and quality parameters (Tables 32 and 33). Corn silage yields ranged from 20.7 to 27.9 tons ac^-1 with the top performing variety, B94T73R, yielding similarly to only one other variety, B94T73SX. Crude protein (CP) averaged 8.23% with the top performing variety, 38N85, containing 8.80% protein. Protein levels were decent despite dry conditions that could limit nitrogen availability and negatively impact protein levels. Acid detergent fiber (ADF) and neutral detergent fiber (NDF) contents averaged 23.4% and 41.0% respectively. The lowest ADF and NDF contents were produced by variety B97T04SXE which had 21.1% ADF and 37.8% NDF. Four other varieties also performed statistically similarly to this variety in terms of both ADF and NDF content. Starch varied widely by variety ranging from 27.8% to 36.2% with the top performing variety, B97T04SXE, containing 3.6% more starch than the next highest variety. Water soluble carbohydrates (WSC) ranged from 5.99% to 7.81%. Total digestible nutrients (TDN) ranged from 61.9% to 64.6% with four other varieties performing similarly to the top performer. uNDF240 is the portion of the NDF fiber that remains undigested after 240 hours of exposure to rumen fluid. uNDF240 ranged from 10.2% to 12.8%. Net energy of lactation (Nel) ranged from 0.625 to 0.679 Mcal lb^-1.

Table 32. Corn silage quality parameters by variety.

* Varieties with an asterisk performed statistically similarly to the top performer in bold

‡LSD; least significant difference at the p=0.10 level.

Table 33. Predicted milk yield by variety.

* Varieties with an asterisk performed statistically similar to the top performer in bold.

‡LSD; least significant difference at the p=0.10 level.

Post-harvest ground cover was also significantly impacted by corn variety, however, cover crop biomass was not (Table 34). Ground cover ranged from 20.2% in plots with variety CP3499VT2P to 38.4% in plots with variety SW3768. Interestingly, high corn yield was not clearly associated with lower ground cover. For example, the second highest yielding variety, B94T73SX, had a statistically similar level of ground cover as variety SW3768 which had the highest ground cover but yielded almost 2.5 tons ac^-1 less than B94T73SX. This is important as it demonstrates that interseeding cover crops can be successful without compromising the yield of the corn crop (Figure 18).

Table 34. Cover crop characteristics by variety.

†Treatments that share a letter performed statistically similarly to one another.

‡LSD; least significant difference at the p=0.10 level.

Effect of corn architecture and interseed timing- Borderview Research Farm, Alburgh, VT

Deciding when to interseed a cover crop is challenging. On one hand you want to allow the cover crop time to establish before the corn blocks the light, but on the other hand, you don’t want the cover crop to compete with the establishing corn for resources. In addition, you want to make sure that corn herbicides do not impact the interseeded cover crop. Generally, corn can be interseeded anywhere from the V2 to V6 growth stage. After V6, most interseeding equipment is not tall enough, increasing the risk of damaging the corn crop.

Light available at the time of interseeding varied dramatically across the timing treatments (Figure 19) The arrows indicate the date the corn was interseeded corresponding to the V2, V4, and V6 growth stages. At the V2 and V4 growth stages, virtually none of the PAR was being obstructed by the corn canopy. However, by the time the corn reached the V6 stage, the canopy was already obstructing almost 50% of the light. Light infiltration continued to decline by approximately 10% each week until only 10% of the total light was infiltrating the canopy. This is the level that remained through the remainder of the season.

Despite the significant reduction in light available to the germinating cover crop in later interseedings, all timings supported similar cover crop establishment (Table 35). Post-harvest ground cover averaged 29.2% across the three timings and did not differ statistically. However, the majority of the ground cover was contributed by weeds, not interseeded cover crop species. This suggests that weed pressure throughout the season may have contributed to poor cover crop establishment and performance. As shown in Image 1, the dominant species that established and survived was the tillage radish. This is likely due to its large taproot that allowed it to access the limited moisture in the soil that the clover and annual ryegrass could not. Its wide leaves also allow it to compete for light resources better than the other species. Although the cover crops were assessed approximately 20 days after the corn was harvested, cover crop biomass was still too small to adequately sample. The corn in the trial yielded well averaging 23.7 tons ac^-1 and did not vary across interseed timings. It is important to note that no damage was caused to the corn crop either from equipment at later interseedings or competition from the cover crop.

Table 35. Corn and cover crop characteristics by interseed timings, 2020.

NS; Not statistically significant at the p=0.10 level.