What are resources for learning more about no-till farming?

AFHGlen · May 19, 2023, 12:29pm

It seems like green manures are one of the challenges for no till farming because in conventional farming they are tilled into the soil which doesn’t happen with no-till.

So, without the green manure being tilled into the soil, what happens? How do those tons of organic matter get into the soil to promote the good things that organic matter does in the soil? Sure earthworms might carry some of it down but how can that compare to plowing under tons and tons of fresh green organic matter. Besides, how much of the value of the organic matter is lost to the drying effects of the sun?

I’d like to know of teaching/learning resources that address these sorts of issues. The things I’ve read over the years ignore these seeming bottlenecks.

ssnyder · May 19, 2023, 1:40pm

I’ll be very interested to hear about teaching/learning resources from the network. This comprehensive review on the broader issues of soil health might be helpful in the discussion, though I acknowledge it does not necessarily answer your questions about the mechanisms and drying effects of the sun. Great questions, that I hope others can weigh in on.

Stacy_Swartz · May 19, 2023, 6:37pm

Hey Glen,

This is a fantastic question! Recommendations for green manure/cover crop (GMCCs) management differ based on your climate and season. Most recommendations for tropical and subtropical agroecosystems are to leave cover crop residues on the surface, to slow decomposition and cover the soil, thereby cooling the soil and retaining soil moisture as well as Nitrogen (e.g., Vieira et al., 2009; Erenstein, 2002). This is the opposite in temperate climates! What’s the reasoning behind this? It is multifaceted but has a lot to do with losses from the system. I did my master’s research on this topic, so I apologize for the following rant.

Nitrogen and carbon decomposition occur faster when plant residues are incorporated than left on the soil surface in tropical conditions (Lynch et al., 2016; Jani et al., 2019; Mulvaney et al., 2017; Mulvaney et al., 2010; Abera et al., 2014). In warm, wet climates microbial breakdown and leaching of nutrients is rapid. When residues are incorporated, the increased access to residues increases the microbial breakdown of N and C (among other things). This also heats up and areates the upper horizons of the soil. These increases in losses due to higher moisture and temperature outweigh the losses that would be encountered solely by N volatilization caused by drying in the sun on the soil surface. The thicker the cover crop, the better. The top layer of residue helps protect the lower layers as well as the soil. The difference between practices would be less if the cover crop or residues are not thick.

What exactly is the numerical difference between incorporating and not incorporating is a much more detailed question that depends on your specific season, let alone climate. The wetter and hotter your season of residue decomposition is, the better it is to leave residues on the soil surface rather than incorporate them. The cooler, drier your season after incorporation is, the better it is to incorporate to protect from N volatilization. There are studies that vary across the literature showing different numbers on N and C losses given both practices in unique agroecosystems, but general guidelines are to incorporate in cool climates and leave residues on the soil surface in hot climates.

As far as teaching this, below is a screenshot of the Slide I show ECHO interns when talking about this topic. When I worked in East Africa with some farmers, I took samples from farms that were no-till vs. tilled and asked farmers which one they would rather have on their farm and why and then shared what the farmer’s practices were. I’m happy to share more if you need!

References:

Abera, G., Wolde-Meskel, E., Bakken, L. 2014. Unexpected high decomposition of legume residues in dry season soils from tropical coffee plantations and crop lands. Agronomy for Sustainable Development 34 (3):667-676.
Erenstein, O. 2002. Crop residue mulching in tropical and semi-tropical countries: An evaluation of residue availability and other technological implications. Soil and Tillage Research 67:115-133.
Jani, A.D., Mulvaney, M.J., Enloe, H.A., Erickson, J.E., Leon, R.G., Rowland, D.L., and Wood, C.W. 2019. Peanut residue distribution gradients and tillage practices determine patters of nitrogen mineralization. Nutrient Cycling in Agroecosystems 113:63-76.
Lynch, M.J., Mulvaney, M.J., Hodges, S.C., Thompson, T.L., and Thomason, W.E. 2016. Decomposition, nitrogen and carbon mineralization from food and cover crop residues in the central plateau of Haiti. SpringerPlus 5(1):973–981.
Mulvaney, M.J., Balkcom, K.S., Wood, C.W., and Jordan, D. 2017. Peanut residue carbon and nitrogen mineralization under simulated conventional and conservation tillage. Agronomy Journal 109:696-705.
Mulvaney, M.J., Wood, C.W., Balkcom, K.S., Shannon, D.A., and Kemble, J.M. 2010. Carbon and nitrogen mineralization and persistence of organic residues under conservation and conventional tillage. Agronomy Journal 102(5):1425–1433.
Vieira, F.C.B., Bayer, C., Zanatta, J.A., Mielniczuk, J., and Six, J. 2009. Building up organic matter in a subtropical pleudult under legume cover-crop-based rotations. Soil Science Society of America Journal. September-October:1699-1706.

Andrew_L · May 19, 2023, 9:40pm

This is very helpful Stacy, thanks! I’ve often wondered the same thing.

AFHGlen · May 20, 2023, 12:57pm

Stacey, as always, you are very helpful. If you have more of those slides to share, I am interested.

A follow up question. It seems like a tillage system would have more organic matter in the soil for feeding the micro organisms and holding moisture. Is that true?

To keep things more simple and easier to compare till vs no-till, for this conversation, let’s assume 2 neighbors in south Florida grow the same green manure crop at the same time. One tills it into the soil and the other cuts it in place…chop and drop. How would the two fields compare 1 year later and 2 years later in terms of the amount of organic matter in the soil? Lets also assume both fields had the same history for the previous 2 years before this test,

Chris_Evans · May 20, 2023, 2:49pm

A great response from Stacy. An example of the folly of trying to impose a temperate (tillage) system on the tropics. Mind you now even in temperate systems there is a growing bank of evidence pointing to no/min. till, with cropping systems and machinery being modified accordingly. To me the effect of tillage on soil life is the clincher - breaking up the mycelial networks and distrupting soil biology (compounded by adding chemical fertilizers and poisons) that is responsible for building fertillty and access to nutrition. See soil food web learning resources for more info on this.

Stacy_Swartz · May 22, 2023, 6:39pm

Glen,

A great follow-up question. There are definitely larger-system contexts that would make organic matter content vary. In paddy rice production systems, organic matter retention is much higher with tillage regardless of climate because the permanent flood over the rice cultivation helps retain the organic matter (but also causes more methane production than alternate wet-dry rice systems). And tillage makes rice cultivation so much easier, so I didn’t want to miss mentioning that. Farmer management practices should always be taken into account when promoting GMCCs.

I love a good case study! Soil type would make a huge difference in this scenario in Florida. If the fields have sandy soils, their organic matter content probably hasn’t changed very much in 1 to 2 years (assuming 1 cover crop over the summer months which is typical of South Florida). If they have muck soils or the rocky soils of the southern tip of Florida, they may see a jump of up to a percent or two (which is pretty great but also depends on the species they are using). GMCCs are a great low-cost tool for increasing soil organic matter over time, but results are slow, especially in degraded soils. Poeplau and Don (2015) analyzed 139 different GMCC studies and summarized that over 54 years, the studies showed an annual change of 0.32 Mg per ha (0.893 pounds per acre) of soil organic carbon (average soil depth sampled was 22 cm).

But for the sake of this example, the farmer who incorporated their cover crop most likely has less organic matter in their system compared to the farmer who left their residues on the soil surface (if the cover crop was productive). Residue decomposition and use are increased in hot, humid contexts when residues are tilled into the soil. Tillage also breaks up residues into smaller pieces which increases decomposition rates even faster. High nitrogen content of residues like what many leguminous cover crops have also increases microbial decomposition in soils though I’ve not seen many research articles that look into this component.

Something that maybe needs to be explained further so that this makes sense is the stability of carbon in agroecosystems. Carbon is divided into labial portions (easy to break down) and recalcitrant portions (difficult to break down). As carbon breaks down, some of it remains in the soil, some of it goes back into the atmosphere as CO2, some dissolves in water, and some is taken up into the bodies of organisms in the soil etc. So as we increase the decomposition rate of residues in hot, humid conditions, we also increase carbon use and cycling back into the surrounding ecosystems. I hope this makes sense. Here’s a graphic I made a while back.

Leaving residues on the soil surface is a “best practice” for hot, humid climates for long-term soil health. Also, as a fun fact, where ECHO is located in Florida has a spodic layer. This layer in the soil horizon is where the dry season water table resides and is where much of the organic matter settles as it percolates through our sandy soils. Here’s a picture of what that looks like on our farm:

Reference:
Poeplau, C. and Don, A. (2015) Carbon Sequestration in Agricultural Soils via Cultivation of Cover Crops—A Meta-Analysis. Agriculture, Ecosystems & Environment, 200, 33-41.

David_Uhr · June 9, 2023, 6:46pm

Another great resource for no-till is the Farming God’s Way website, where you can download a short Field Guide and the more in-depth Trainer’s Reference Guides at no charge, in several languages. Resources

Dan_Janzen · June 13, 2023, 5:49pm

I think Stacy had a lot of really good things to say and definitely has done a lot of study on the issue. I think it is easy to try to oversimplify answers and just look at conservation or organic components but agriculture is much more than that. We have to make choices based on income generation (income per hour & return on investment), even long-run sustained income generation which is why we pay more attention to the organic matter management options. We are all called to the Great Commission and we generally choose highest income systems so that we can maximize the time and and money dedicated to the Great Commission or charity which is technically part of the Great Commission. There is no one-size fits all. We may like a particular type of agriculture but we should all be challenging one another to choose the type of agriculture that maximizes our opportunity to change the world most strategically. We often get distracted even in our agricultural systems with some other goal than the Great Commission. There are a lot of excellent agricultural systems but an excellent system is not most excellent if it does not meet the best income per hour or return on investment criteria. People seldom talk about that. I grew up on a very diversified farm and we did not use any cover crops or no-till at all and we made a tremendous amount of money because we were good managers (including managing the soil). We were not degrading the soil and it has stayed highly productive. For zucchini we brought in truck loads of poultry waste mixed with sawdust and we were awarded the best producer award by the cannery. But we did not use manure, cover crops or organic matter additions for other crops and I am not sure I would have changed that as familiar as I am with other systems including cover crops and no-till systems. We used commercial fertilizer and crop rotation. The Florida summer is more tropical but the winter is more temperate. Fertility is a problem in the more sandy soil regions.
Now I work in East Africa where I use a lot of systems depending on the situation. There are times when growing a green manure after the harvest of the crop or seeding it in as a relay or intercropping it in (as long as it does more benefit than harm in competing for light/space, nutrients, and water) makes a lot of sense. The intercropped legume may also be a food crop. There are times when a cover crop or weed vegetation is sprayed (in organic systems may be crimped to kill it) and then laid down and then planted in a no-till system.
I like Roland Bunch’s Restoring our Soils book and also the book series by Hugues Dupriez which is excellent and I have tried to get the ECHO book store to sell it many times. There is an incredible amount of information in those two sources that could be helpful to you. There are a lot of materials written by people who have other goals besides income and the Great Commission tied together or have never grown commercially on a large enough scale or in a way that is generating income in a competitive way (that do not charge excessively for hyped-up value that is not backed up scientifically—i.e. Joel Salatin).
In addition, much depends on your existing equipment because efficiency of production is very important. There are systems that smaller farmers use due to the fact that they don’t have much money for manure/fertilizer or have equipment or irrigation. Mulching is great when you are producing vegetables and not on a large scale but limited access to mulch causes one to think more about a more efficient intercropping system where the intercrop (possibly not so much the first year) provides some of the soil improving characteristics of the mulch. That is beyond what crop rotation can supply. Irrigation reduces the value or necessity of mulching some but it still may be important to use mulch. I prefer organic matter on the surface and I consider it a benefit that the organic matter keeps the soil cool and moist and increases organic matter content. I don’t think the sun drying out the mulch is much of a concern.
When you have irrigation and equipment or adding these to your production then some of what were the most productive techniques without them become less efficient if they are labor intensive and you switch to a different system that fits your irrigation program and equipment.
I like no till but so many people are not using herbicides in the no-till systems and therefore have become much less productive than possible with the use of herbicides and no-till. And I don’t accept people telling me that they are too poor to buy a sprayer or use herbicides. The first season a sprayer can be made from a bottle and/or people can share the cost of a sprayer or custom spraying and a quart (or more) of glyphosate or a selective herbicide. Spray technology is one of the fastest way to increase efficiency and the sooner people start using it the more quickly they will launch into higher income crops and production systems.
When people are just starting I recommend focusing on volume of organic matter rather than quality. There are so many things people do that impact soil fertility very little because they did not impact the soil in sufficient volume.
One of the great opportunities for improving management of cover crops or living mulches is ripping to control the root systems of intercropped legumes so that they release much of their nitrogen and other nutrients at the right time and competition is much reduced. And people need to start talking about slashing the intercropped legumes. That way you can grow a fast growing perennial legume that will grow all through, or at least part way through the dry season and fix a lot of nitrogen. Otherwise you have to grow a taller crop and delay planting the perennial legume a month or so and then the overall productivity is less. I believe in general because we are not considering many of these improved methods we are very far from peak production and particularly far from peak income generation and then extremely far from peak participation in the Great Commission.
Our philosophies of production are increasingly infiltrated by faddish ideologies that have strayed far from the right objectives. Cover crops, living or dead mulches, incorporated or left on the surface must remain a means to an end (supporting our families and rest going to the Great Commission) but much of what I see today is people promoting their ideal way of production as an end to a means or to explain it another way using a system for the sake of some other objective due to ideological distractions.