Fall is upon us, once crops come off the field farmers need to make informed decisions about what tillage method to use.
In this week’s edition of Growing Possibilities, we ask: what is the effect of tillage on soil microbes? The short answer is that microbes tend to do better when the soil is left undisturbed. The long answer is that how you choose to till your field depends on a lot of factors. It’s important to know your soil. Soil conditions, such as topsoil depth and soil type, will greatly impact the success and effect of your tillage method. Tilling is performed in multiple ways and for multiple reasons, such as weed and pest control, soil leveling, and to incorporate crop residues & fertilizers (1). The method of tillage – conventional tillage, minimal or reduced tillage, and no tillage or zero tillage – have different impacts on the microflora within the soil.
Conventional tillage (CT) occurs every year, sometimes twice a year, in the fall and spring. Advantages to CT include loosening and aerating the soil, allowing for deeper root penetration, warming the soil, controlling weeds, and mixing organic matter, fertilizer, and manure into the soil (2). However, CT is harmful to the microhabitats of the soil microbes. Macroaggregates are torn apart, which scatters microaggregates and disrupts their crucial nutrient cycles. They must then reform their niches, which for a time results in lower productivity in the soil (3).
Aside from the loss of macroaggregates, the disadvantages of CT come from increased wind and water erosion, a loss of soil moisture, and higher costs due to high fuel usage (2). However, choice of CT equipment and depth can have significant differences on the soil. (5).
Minimal tillage (MT) involves tilling your field once every few years, and/or at shorter depths (8). The advantages of MT include reduced soil erosion and associated air and water pollution, reduced fuel, and production costs, and reduced subsurface soil compaction from tractor passes (8). With MT, plant residues are maintained on at least 30% of the soil surface after tilling and tillage passes are reduced by at least 40% (8). MT has been shown to increase diversity, biomass, and enzymatic activity of soil microbes(5). This increases the productivity of the soil, resulting in healthier plants in the successive crop.
However, MT does have its shortcomings such as, increased herbicide use, the risk of disease carryover (from leftover plant residue on the soil surface) and an increase in pests, such as rodents, insects, and pathogens (8). As well, productivity and profitability may decrease if the initial transition from CT to MT is not performed correctly (8).
No tillage (NT), or Zero tillage (ZT), means there is no mechanical disturbance of the soil, and seeding is done directly into the soil or remaining crop residue (2). This lack of disturbance means that micro- and macroaggregates remain intact. Microaggregates are composed of microorganisms and soil organic matter, and are a hotspot for nutrient cycling, as each type of microbe has its own specialty that uses different plant resources (3). Bundles of microaggregates are known as macroaggregates, which are protected by mycorrhizal hyphae like a mesh bag (3). Together they create a rich, healthy soil.
No Tillage also lets carbon build up in the top layer of soil. If you have a well-maintained field with a good microbial balance, this means good things for your field. Carbon feeds the microflora in the soil, so a topsoil (0-5 cm) that is rich in carbon results in higher microbial biomass and enzymatic activity (4, 5). This becomes especially true when cover crops are used (4, 5). Since one of the effects of tillage is weed control, using a cover crop in tandem with crop rotation has the double effect of both maintaining a healthy environment for the microbial populations and controlling weeds (1).
No Tillage also has disadvantages, such as: the initial cost of the equipment necessary to perform NT, the formation of gullies in the field, increased herbicide use (which is detrimental to microbial populations (6)), a risk of disease carryover, and the compaction of heavy soils such as those with clay (7). To note, risk of disease carryover may be mitigated with crop residues and crop rotation (7). For these reasons, many farmers choose minimal tillage.
So, what is the effect of soil tillage on microbial populations? Soil microbial populations tend to do better under NT or MT conditions. However, as pointed out in this blog, there are more factors than just microbial populations at play in your fields. If you are concerned about microbial soil health a good way to rejuvenate microbial populations is to use legumes as a cover/ rotational crop, combined with premium inoculants like those found in our XiteBio® SoyRhizo® and XiteBio® PulseRhizo®. These products not only give a fresh infusion of nitrogen fixing bacteria to the soil but also promote growth and development in the native microbial population.
Resources
- http://www.omafra.gov.on.ca/english/crops/pub811/pub811.pdf
- https://www150.statcan.gc.ca/n1/pub/16-002-x/2008003/article/10688-eng.htm
- https://www.realagriculture.com/2021/01/what-happens-to-soil-microbes-when-you-till/
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5814021/pdf/pone.0192953.pdf
- https://www.sciencedirect.com/science/article/abs/pii/S0038071716300190
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7602795/
- https://www.conserve-energy-future.com/no-tillage-farming.php
- https://sarep.ucdavis.edu/sustainable-ag/conservation-tillage