1 Summary
Tilling is a practice which turns the soil to remove weeds, break compacted soil and prepare the soil for seeding. However, this practice causes damage to the soil system, which results in further problems on a farm. The improvement in resource use and crop productivity from converting from tillage to no-till is comprehensively documented, however, the practice is still continued. Perhaps this is because farmers don’t know how tillage interacts with the soil system. This paper explains how tillage causes organic material loss, soil biology death, diseases and pests, soil structure destruction and weeds. The author believes that once these interactions are understood, it will be an obvious need to look for better solutions. Each farm needs its own study for an appropriate solution, but the best general concepts are to not disturb the soil, and add a lot of organic matter.
2 Introduction
“Tilling is the practice of digging up, turning over, or otherwise agitating the soil with mechanical tools—typically a plow or disc” [1]. Tilling is typically used for removing weeds, increase infiltration, putting crop residue back in soil and aeration. It is an easy, yet expensive solution for preparing the land.
However, these benefits come at a high cost of soil erosion, pests and disease, soil compaction and many others, which form a vicious cycle with tilling [2].
It is well known that converting to no-till can improve productivity and efficiency of all resources, especially water [M3]. In fact, it has even been demonstrated that no-till can produce higher yields in Jordan [4]. But still many farmers continue to use conventional tillage. Perhaps it is because they don’t know the source of the problems which they use tillage to try to solve. Rather than trying to demonstrate the benefits of converting to no-till, this paper focuses on clarifying what happens to the soil system when tillage is used. Once the system is understood, the author believes it will be an obvious choice to look for an alternative solution which suits the farmer.
There are three mains types of tillage [5]:
Conventional tillage – tilling enters deep into the soil and does significant turning
Conservation tillage – tilling tries to minimize disturbance to a shallow depth
No till – a methodology which very slightly disturbs the soil, while adding organic content to the soil with mulching and cover crops
The focus here is on conventional tillage because it is familiar and is the worst case.
The paper proceeds by explaining what happens in the soil during conventional tillage, and then hints at solutions.
3 What happens when we till?
Soil is composed of clay, sand, silt, organic matter, air and water. Each of the items interact and produce certain effects in the soil. Each interaction is disturbed by tilling, as will be discusses in this section.
3.1 Organic material loss
One of the most important components is air. Air is needed in the soil for microorganisms to break down organic material. Usually, the biology in the soil (E.g. worms, frogs, beetles) will aerate the soil to levels which are in balance with the particular soil system. But when we till, we cause excessive air to enter the soil, which accelerates oxidation of organic matter (released as CO2), much faster than any natural rate [3] [8]. Several years of continuous tilling without replacing the organic matter, will quickly deplete the organic matter in the soil.
3.2 Soil Biology Death
The organic matter is the energy source for biology. The organic matter contains protein (from animals), chitin (from invertebrates), lignin (from wood) and cellulose (from leaves) which soil biota use to make sugars for cell functioning. With the loss of organic matter due to unnatural aeration, the biology quickly dies out.
The biota are further stressed by another factor… Tilling exposes biota and their eggs/spores/offspring to harsh heat and UV from the sun, which kills them and sterilizes the soil [8]. Additionally, every time the soil is turned, the environment of the microbes get disturbed, which they can’t tolerate for long.
With no soil biology, crop residues do not get taken into the soil, but rather lie on surface and dry out. This is what motivates farmers to think that they should turn the residues under the soil, forming a vicious cycle [8].
3.3 Diseases and Pests
The biota in the soil are what protect plants from disease and pests [8].
In natural systems, diseases are present in the soil, but seldom cause plant infection. This is because in nature the plants are exposed to diseases in small amounts, allowing the plants to develop resistance without getting infected [8]. But when we till the soil, the diseases vanish along with the biota and organic material. This means that a new crop does not get the opportunity to develop resistance to disease while it is young. If a disease returns later, it will be very easy for the crops to get infected, which we often see [8].
Pests are controlled by whole microbe community interactions. In natural soil there is a huge variety of organisms, creating a system where no organisms can dominate [8]. I.e. the web of organism keeps each organism in check. But when the diversity of organisms is reduced, certain organisms can proliferate and infest a crop.
In consultation with 2 organic farms in Jordan, 1 in Vietnam and 2 in South Africa, they all say that the key to preventing pests and disease is to maintaining biology in the soil.
3.4 Soil Structure Destruction
A healthy soil has the following basic structure, and each one is affected by tilling (except sub-soil):
3.4.1 Litter Layer
The litter layer is a layer of organic material which has fallen on the ground from leaves and animals. It acts like a sponge – intercepting any runoff, and as a cover for the soil, protecting it from evaporation and wind [3]. In agriculture in general, sometimes the crop residue is left on the field, which would normally contribute to the litter layer, but tillage is used to turn the residue under the soil. This activity prevents the litter layer from building up, thereby leaving the soil exposed to the sun until the next crop grows. In natural systems, the litter layer does not get turned under the soil, but rather builds on top of it while biota decompose them [8]. The litter eventually becomes the organic content of the soil.
3.4.2 Soil with Roots
Inside the soil, the organic content, also known as humus, interact with clay particles to form a molecule called the Clay-Humus Molecule (CHM). The CHM has a negative charge and allows ions to bond with it. Plants can extract the ions from the CHM and exchange it for a Hydrogen proton [8].
Most minerals/nutrients, which plants need, are ions, which means they can be dissolved by water.
This discussion is important because if there is little organic content in the soil, it will be easy for nutrients to be washed through the soil during irrigation or rain [8].
The roots of plants act as channels for water when it rains or irrigation. They also act as aeration holes when the plant dies and the roots decay [8]. Tilling fills in these holes, making infiltration more difficult.
3.4.3 Mycelium
The mycelium layer is a very thin layer of fibers like a web which are part of mycelium (eg mushroom) organisms, typically occurring within 5-10cm of the surface [9] [8]. The mycelium layer acts as a net to catch ions which may be washing through the soil. When we till, we break the mycelium layer, reducing the ability of the soil to hold nutrients [1] [8]. We also lose the important decomposing functions of the mycelium.
The mycelium is especially present near trees, because both of them form a symbiotic relationship…The trees feed sugar through their roots to the mycelium, and the mycelium break down organic matter to release nutrients and water to the tree [8].
3.4.4 Surface sealing
A good soil will have more than 5% organic content [8]. The organic content holds the soil together by providing tension strength [8]. It also holds pores open for water to infiltrate, and air to circulate [3].
Tilling breaks the soil structure so the soil becomes fine grained after several years [10] [10]. When the rain hits the soil, the grains easily move, and quickly seal up any pores at the surface, preventing infiltration [3]. Rain then quickly runs off, carrying topsoil with it [11].
3.5 Weeds
Weeds are plants which grow where we don’t want them to – there is not particular species which can be called a weed [8]. Weeds grow in disturbed or poor soils, and are few of the plants which can actually do so. But the understanding of weeds is changing as we realise that weeds are better described as ‘pioneering plants’ rather than ‘pests’ [8].
We’ve come to realize that weeds play the role of repairing the soil so that natural vegetation can return. Weeds repair the soil by adding organic content to the soil when they die. Many years of depositing their residues on the soil, will increase the organic content of the soil, which will attract soil biology which will help restore the nutrients in the soil [8]. When considered this way, this makes their quick growth and short lifecycle an advantage.
When the soil is repaired, other natural vegetation will take over and the system will start to rebuild. The weed seeds will lie dormant in the soil until the soil is disturbed again.
Weeds are often seen as a problem when they become excessive on a farm, because they compete with the crops we are trying to maximize. We then use the tillage technique to remove them, which further disturbs the soil [8]. In order to manage weeds, we should look for techniques which minimize disturbance to the soil. Additionally, weeds need a lot of sunlight in their early stage of development, therefore, covering the ground with mulch would prevent them from growing [8].
4 What can we do?
Each farm requires its own study to determine which are the best techniques that suit them. The best thing we can do is try to reduce disturbance to the soil. We should also add more organic content to the top layer of the soil. Four key changes which could be made:
We should avoid tilling, especially under trees. (Tilling might be needed only initially when rehabilitating compacted soil)
Add a lot of mulch, for several years [12]
Use cover crops to protect the soil from sun and wind
Leave root stubs in ground – acts as water path, will decay as organic matter
Useful resources to find solutions for one’s self can be found at www.RodaleInstitute.org.
Additionally, the following links are good videos demonstrating the difference between long term tillage and no-till.
5 Conclusion
This paper explained how conventional tillage cause disruption of the soil system.
Organic matter is lost through accelerated aeration
Soil biology is killed by exposing underlying soil to the sun
Diseases and pets become a problem because diversity in the system is decreased
The structure of soil is destroyed which prevents infiltration and increases nutrient loss
Further projects are needed to demonstrate these principles to farmers.
6 References
1. Rodale Institute. Organic No-Till. 2019. https://rodaleinstitute.org/why-organic/organic-farming-practices/organic-no-till/. Accessed 07-Jan-19.
2. Nunes MR, van Es HM, Schindelbeck R, Ristow AJ, Ryan M. No-till and cropping system diversification improve soil health and crop yield. Geoderma. 2018;328:30–43. doi:10.1016/j.geoderma.2018.04.031.
3. Blanco-Canqui H, Ruis SJ. No-tillage and soil physical environment. Geoderma. 2018;326:164–200. doi:10.1016/j.geoderma.2018.03.011.
4. Abu-Hamdeh NH. Effect of weed control and tillage system on net returns from bean and barley production in Jordan. Canadian Biosystems Engineering. 2003.
5. All About Food. The 3 Types of Soil Tillage. 2019. http://allaboutfood.aitc.ca/article/3-types-of-soil-tillage.php. Accessed 08-Jan-19.
6. Summers. Conventional Tillage. 2019. https://summersmfg.com/solution-application/conventional-tillage. Accessed 08-Jan-19.
7. IEASSA. What is No-Till Farming. 2018. http://ieassa.org/en/what-is-no-till-farming/. Accessed 08-Jan-19.
8. Pearson TF. Introduction to Permaculture. Dibeen Eco Farm; 26 Dec 2018.
9. Schmidt R, Mitchell J, Scow K. Cover cropping and no-till increase diversity and symbiotroph: Saprotroph ratios of soil fungal communities. Soil Biology and Biochemistry. 2019;129:99–109. doi:10.1016/j.soilbio.2018.11.010.
10. Rodale Institute. Farming Systems Trial. 2019. https://rodaleinstitute.org/science/farming-systems-trial/. Accessed 07-Jan-19.
11. Gonzalez JM. Runoff and losses of nutrients and herbicides under long-term conservation practices (no-till and crop rotation) in the U.S. Midwest: A variable intensity simulated rainfall approach. International Soil and Water Conservation Research. 2018;6:265–74. doi:10.1016/j.iswcr.2018.07.005.
12. Pareja-Sánchez E, Plaza-Bonilla D, Ramos MC, Lampurlanés J, Álvaro-Fuentes J, Cantero-Martínez C. Long-term no-till as a means to maintain soil surface structure in an agroecosystem transformed into irrigation. Soil and Tillage Research. 2017;174:221–30. doi:10.1016/j.still.2017.07.012.