This proposal seeks to determine if planting corn into standing, un-rolled cover crops negatively affects corn emergence and yield when compared to rolling cover crops prior to planting. Furthermore, it seeks to compare the use of row cleaners to create a bare soil strip around the seed slot versus rolling a cover crop adjacent to the seed slot, and its effects on corn emergence, slug damage and yield. The information gained from this proposal will be utilized to help farmers and educators quantify potential risks of planting into standing cover crops and will provide guidance in equipment setup for those wanting to adopt or refine planting green techniques.
The process of ‘planting green’ or planting a cash crop into a living, standing cover crop (figure 1) has become increasingly popular in the last 5 years. Benefits of the practice include increased biomass production of the cover crop, reduced soil erosion and increased soil cover that provides habitat for beneficial organisms and buffers soil temperature fluctuations. (Reed, et al., 2019).
The implementation of the planting green concept varies widely among farmers. Early attempts included rolling with a cultipacker prior to planting or planting cash crops into standing covers without rolling. The practice evolved with the use of roller-crimpers to flatten cover crops prior to planting. More recently, rollers have been adapted to the planter frame (Dawn ZRX cover crop roller), combining two operations into one pass. This allows rollers to be mated to wider planters and avoids the need to modify tractors, which may be promising for widespread adoption of the practice.
While the roller-crimper has been an effective tool for planting into standing cover crops (figure 2), the enthusiasm and promotion of the practice has led to many farmers attempting to plant green without utilizing a roller-crimper, instead planting corn directly into tall, dense cover crops. Much of this has occurred when planting green has been used as a ‘rescue’ when cover crops have not been terminated in a timely manner. Unfortunately, many farmers reported poor corn emergence when planting green into standing, un-rolled covers (figure 3) resulting in a negative opinion of the practice due to what may be poor execution of the concept.
Research on corn emergence demonstrates that when plants emerge at an uneven rate, they compete with each other, with late emerging plants showing reduced per-plant yields (Boomsma & Vyn, 2007). In addition, un- emerged plants result in lower stand populations which correlates with lower yields. Factors that promote even emergence include consistent soil temperature and moisture in the seed zone and even light exposure to the seed row. As important as these concepts are, they have not been widely documented in printed outreach materials or general discussions of the practice.
For planting green to continue as a popular and growing practice, there should be a greater understanding of how the practice affects corn emergence. This includes demonstrating and quantifying the risks of planting into un- rolled cover crops and the benefits of rolling prior to planting. Therefore, an accurate side-by-side comparison of planting green into standing cover crops and its effects on corn emergence is needed to improve our body of knowledge and promote the successful implementation of the practice. Ultimately, a better understanding of how planting green management practices effect corn emergence will help farmers make better decisions when selecting cover crop species, modifying equipment for planting green and timing cover crop termination prior to planting.
Many studies have documented the effects of late emergence on corn yields. Early research demonstrated that plants emerging 7 and 14 days later than early emergers had yields approximately 2/3 and 1/2 of early emergers, respectively (Ford and Hicks, 1992). Research in Ontario, Canada showed 4% and 8% stand yield reductions when one out of 6 plants was 2 and 4 leaf stages behind the remainder of the stand, respectively (Liu, et al., 2004). A study of emergence in Oklahoma demonstrated that when one out of three plants in a stand emerged late, stand yields were reduced by 3 to 14% when plants emerged two days late and between 10 and 25% when plants emerged 5 days late (Lawless et al., 2012). Observations at 9 locations in Virginia also showed a trend of decreasing per-plant yields for each day that late plants emerged behind the rest of the stand (VA Coop. Ext., 2016).
Multiple guidance documents outline the use of roller-crimpers for planting into standing, living cover crops, with much of the material focusing on cover crop selection and planting rates, timing of rolling and fertility management. However, the effects on corn emergence are rarely noted. Information presented by Steve Groff (formerly presented by Cover Crop Solutions) advises against planting into cover crops greater than 12 inches tall and the PA No-till Alliance cautions against planting in to cover crops greater than 20 inches tall (PA No-Till Alliance, 2017). In both cases data to support these claims is not provided.
At this time there is no known published research as to how planting green into un-rolled and rolled cover crops affects corn emergence. However, Penn State Extension received reports of poor corn emergence in un-rolled cover crops in 2015 and 2016. As a response, educators in the spring of 2017 recorded observations on corn planted into un-rolled cover crops, noting inconsistent emergence, reduced populations and plants having a tall and ‘spindly’ appearance relative to stands planted in rolled or bare fields or where machinery traffic flattened cover crops (Larson, 2018).
A series of observations were recorded in Somerset County, Pennsylvania in corn planted into a cereal rye cover crop. Half of the field was rolled with a cultipacker and half was left un-rolled prior to planting. Plant populations and heights were recorded when plants were at the V5 to V6 leaf stage (table 1). While not structured as an experiment, analysis of the data as a completely randomized design, having lower statistical power than a randomized complete block, showed that corn planted into the un-rolled cover had lower emerged population (p<0.05), greater average plant height (p<0.10) and greater plant height deviation (p<0.01) compared to corn planted into the rolled cover crop. As noted in other reports, many of the corn plants attempting to grow through the un-rolled cover were taller but more spindly than those in the rolled cover.
In addition to a lack of published data of plant emergence in un-rolled covers, there is no documented information regarding the use of row cleaners on corn emergence when planting green. Early designs of planter-mounted roller crimpers utilized a disc-style row cleaner (figure 4), which creates a bare furrow approximately 6 inches wide around the seed slot. However, in attempts achieve nearly 100% ground cover of the rolled cover crop, some farmers eliminated the row cleaner (figure 5), resulting in a rolled cover immediately adjacent to the seed slot. In both cases there appears to be little data as to how the use or absence of row cleaners affects corn emergence when plating green. Personal observations of full-with rollers (no row cleaners) suggests that closing the seed slot is more difficult and that there may be a greater risk from slug damage due to slugs entering the seed slot to consume germinated but not emerged corn plants. Conversely, those utilizing row cleaners claim they reduce slug damage by creating a “dead” zone between the dying cover crop and emerging corn in which slugs are less likely to cross and feed.
Boomsma, C. R., and Vyn., T. J. 2007. Plant-to-Plant Uniformity is Essential for Optimum Yield in No-till Continuous Corn [Online]. Available at https://www.extension.purdue.edu/extmedia/AY/AY-329-W.pdf. Purdue University, East LAyfayette, IN.
Ford, J. H., and Hicks, D. R. 1992. Corn Growth and Yield in Uneven Emerging Stands. Journal of Production
Larson. 2018. Planting Green Impacts on Corn Emergence [Online]. Available at https://extension.psu.edu/planting-green-impacts-on-corn-emergence. Pennsylvania State University, University Park, PA.
Lawless, K., Raun, W., Desta, K., and Freeman, K. 2012. Effect of Delayed Emergence on Corn Grain Yields. Journal of Plant Nutrition. 35:480-496.
Liu, W., Tollenaar, M., Stewart, G., and Deen., W. 2004. Impact of Planter Type, Planting Speed, and Tillage on
Stand Uniformity and Yield of Corn. Agronomy Journal. 96:1668-1672.
Pennsylvania No-Till Alliance. 2017. Planting Into Green Living Cover Crops [Online]. Available at https://panotillalliance.files.wordpress.com/2018/02/plantinggreen_laminatedhandout_2017-1.pdf.
Reed, H., Karsten, H., Tooker, J., Curran, W. S., and Duiker, S. W. 2019. Planting Green 101: Penn State Research Summary [Online]. Available at https://extension.psu.edu/planting-green-101-penn-state-research- summary. Pennsylvania State University, University Park, PA.
Virginia Cooperative Extension. 2016. 2016 Virginia On-Farm Corn Test Plots [Online]. Available at https://www.sites.ext.vt.edu/newsletter-archive/corn-test-plots/2016.pdf. Virginia Polytechnic and State University, Blacksburg, VA.
In 2019, the field sites were seeded with cover crops in preparation for 2020 data collection. Plots at the David Hernley (Bedford County, PA) farm were drilled with cereal rye (VNS) on September 19th at 47 lbs/ac. Plots at the John Johnson farm (York County, PA) were drilled with cereal rye (VNS) at on November 30th at 90 lbs/ac. The higher rate at the York site was utilized due to the much later planting date of the cover crop.