Soil Health Concepts Leading to On-Farm Prescription - Planting Green
I want to begin a new series of articles called Soil Health Concepts Leading to On-Farm Prescription. No one knows the farm as well as an individual farmer who is farming their own land. We consultants, agronomists, etc. provide the science of soil health and cover crop management. This series will address many topics that hopefully will lead to adoption by farmers prescribing these concepts on their individual farms.
I recently returned from meetings in Iowa, where we held seven round-table discussions across the state with many producers, Conservation District Commissioners, and NRCS. One of the topics that came up in our discussions was planting green. The Tennessee Association of Conservation Districts (TACD) recently hosted Steve Groff (Cover Crop Coach, International Speaker, and Cover Crop Farmer) at three meetings. One of his topics was planting green. I am a subscriber of Cover Crop Innovators (covercropinnovators.com) that many cover croppers and consultants are members of this group. Cover crop innovators has a weekly webinar on cover crop topics. Recently, the group covered the 10 hottest trends in 2018, and the number one on the list was planting green. Prior to beginning this article, I quickly reviewed Planting Green on the internet. Many articles were available. I selected three: John Deere, The Furrow, Warming Up to Planting Green; Lancasterfarming.com, 7 keys to Success for Planting into Green Cover Crops; and Penn State Extension, Planting Green - A New Cover Crop Management Technique. The Recent National No-till Farmer's Conference at Indianapolis also had topics on, yes you guessed it, Planting Green.
I began writing Profiles of Soil Health Heroes in December of 2014. Since then we have accomplished 50 Soil Health Heroes. In many of these, I share the farmers' testimonies that many are planting green. So, this topic is not new for Tennessee, but it is one of the hottest topics in the cover crop conversations.
One common denominator one will see in these articles as well as reality of growing a cover crop is that planning is a must. I plan to write a separate article on planning ahead. I will say now that farmers need to plan now for the fall's cover crops as well as terminating over 14 months from now.
So, why is the number one topic among cover crop groups "Planting Green?" Before answering that question let's talk what has been the norm in planting in cover crops. The norm has traditionally been plant brown. I would like to add that if you plant this method, plant crispy. In reading the aforementioned articles, they define brown as 10-20 days after termination. Planting in brown dead cover that is not crispy will result in more wrapping of cover around planter. So, most farmers agree if planting brown, make sure cover crop residue is crispy. The reason for planting brown was to prevent the "Green Bridge" which potential disease and insects would move from cover crop residue to emerging crop. An additional reason many recommend killing covers early and planting brown is the fear of biomass. Most previous research was done comparing similar practices to conventional methods and limit of large amounts of biomass. furthermore, all previous research was done on dis-functioning soils. Also, most previous research was on monoculture cover crop species. We are just now seeing favorable research on multi-species cover crops. Growing covers to a 30:1 or 45:1 ratio is as different from those previous systems as the planting with a mule is to modern day planters. The environment under a diverse cover crops protected by no-till is very different from long-term research on conventional tillage or even no-till without covers. With these differences from diverse covers, techniques such as planting green are not only possible; they are being currently followed by many.
One of the principles of soil health, that is to rejuvenate the soil, is to keep the soil covered. If residues are limited from previous cash crop or if a cover crop is killed at a short height, that is a low carbon to nitrogen ratio (C:N), the residue from the cover crops will not last very long and we will not see a change in the function of the soil. If we want to see cover crop benefits other than erosion control, such as the govern of soil temperatures in the summer, provide protective armor to resist raindrop displacement, increase soil carbon, and many other benefits, we need more residue. For residues to persist through the season, they must have time to grow and reach a higher C:N ratio. We must let covers grow to a point of pre-fruiting stage (boot stage on grass and early to mid-bloom stage for legumes). Only then will we provide active carbon that will result in more vibrant soil biology, and soil health will improve.
Now, many farmers in Tennessee are using multi-species cover crop mixes. Also, many farmers are now in year four plus in these systems. So, I think it is important to define planting green. It simply means planting in a living cover crop that is killed either immediately before or sometime after planting, usually same day or two-three days later. The reason, we are not seeing the green bridge is that the diversity of covers resulting in diversity of soil biology. Diversity provides a policing effect of soil biology where disease species are controlled by other soil biology. Also, beneficial insects are building up in multi-species cover crops and control pests from the green bridge. Another finding with many farmers is that even slugs will tend to feed on the green cover other than just the emerging crop. Another article will be written on slugs and beneficial insects at a later time.
The biggest reason for planting green is to reap the benefits of the cover crops in the narrow planting window from cover crops to planting the cash crop. Normally corn is planted prior to soybeans. Some farmers are planting earlier maturing soybeans and may be planting around the same time. The point is in these earlier planted crops, farmers traditionally would kill these covers at a few inches tall which resulted in very little root growth as well as above biomass growth. One of the major objectives in growing cover crops is to increase soil carbon into the soil. To do so, one must keep the cover crop growing longer. Planting green allows for two to three more weeks of growth usually double or more in height and depth of roots. With increase growth, we also see maturing cover crops with a higher C:N ratio. Later planting crops are easily planted green.
Another reason to plant green is to manage moisture. One of the problems of planting brown or crispy is that after killing cover crop 14-21 days earlier, and then rain sets in. The soil will be like a sponge and soil will remain cold and wet, thus delaying planting. Farmers will have to wait until soil warms up before planting. Planting green keeps a biological pump going up to the time of planting. The cover crop will continue to efficiently uptake moisture. It will also continue to leak carbon out of the roots feeding soil biology. Springs in 2017 and 2018 were wet and cool. Keeping a cover crop growing removes excess water. Also, a concern to consider in cool wet weather, farmers should only plan to only terminate while green only what they can plant in a day. Terminating more cover than you can plant can put you in the previously discussed problems of having dead cover and excess moisture. Another factor to consider is if weather forecast is dry for the spring, farmers are wise to go ahead and terminate to preserve moisture. This is especially wise if no moisture is on the horizon near planting time.
As I earlier said, planting green provides farmers the opportunity to reap benefits by extended growth usually 2 - 3 additional weeks with additional C:N ratio. One major benefit of more growth is better weed suppression. Some farmers plant in standing covers. Hopefully, most of cover is knocked down at planting. If not shading could hurt cash crop's growth. Other farmers are using roller/crimpers or some object such a cultipactor, smooth rollers, utility poles, etc. to manage cover in one direction. When covers are laid down with extra growth, weeds are suppressed by choking effect. Those who plant rye in their mixes are having the effect of allelopathy, which releases chemicals with decaying rye that kills germinating broad leaves. I will address allelopathy planting concerns for cash crop in another article.
Besides weed suppression, the extra growth from planting green speeds up improvements in soil function. All farmers desire the water cycle to return to their fields. Increased carbon production, from more solar energy, will aggregate the soil and improve soil structure and increased water infiltration. Carbon increases, by extended growth of covers, will provide better water holding capacity. The better growth from planting green provides more residue which will keep soil cooler in later summer and reduce moisture losses. This provides less yield losses during short-term droughts. All soil functions or at least most are biologically driven. With planting green and extended growth, more carbon and root growth provide more food for soil biology.
Farmers have shared that planting green have less hair-pinning. The planter cuts easily through green matter. Extended root will uptake more nutrients and cycle the nutrients with less water quality impacts. With legumes in the mix, extending growth for up to three weeks, will provide more nitrogen to be fixed by rhizobia bacteria. This means fewer nutrient inputs. Reports from Pennsylvania says that slugs are less damaging in cool, wet soils when covers were planted into green. Slugs tend to eat on dying covers over emerging crops. More on slugs in later articles.
With more persistent residue remaining through the season, there is less soil splash and less disease from the soil splash. Of course, more residue produced will result in less soil losses. Planting green requires good planting equipment. I will not comment on equipment because, I have seen different methods that yielded excellent stands. Farmers are good at planting a seed and getting great stands. Planting green is a tool that can help farmers yield the more benefits from cover crops due to extended growth. For more information on planting green or soil health, contact your local NRCS or Soil Conservation District Office.