SINCE the United Kingdom's Second Agricultural Revolution of 1650 to 1900, modern farming has revolved around excessive tillage, mechanically cultivating the soil to enhance fertility and maximise crop production.
However, the heavy reliance on tillage raises concerns over its long-term impacts and prompts a reconsideration of alternative approaches.
Many farmers believe that the more they till their fields, the more bountiful their yields will be. However, excessive tillage has drawbacks, particularly its impact on climate change.
The practice entails intense and frequent soil disturbance, disrupting the natural composition and structure of the land.
Although tillage serves specific purposes contributing to agricultural practices, such as controlling pesky weeds and integrating organic matter, its adverse effects on the climate cannot be overlooked.
In Zimbabwe in the 2007/8 farming season, a heavily politicised farm mechanisation scheme saw ruling party-aligned smallholder farmers receiving tractors, disc harrows and other tillage equipment.
The nation suffered unprecedented bad harvests, exposing millions to hunger and starvation.
While other structural factors intersected with the famished nation, some challenges came with applying the new equipment on previously under-tilled soils in communal agriculture.
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Soil degradation
Excessive tillage disrupts the soil structure, leading to various forms of soil degradation. In regions with heavy rainfall, excessive tilling causes soil compaction, reducing its ability to absorb water.
This increases the vulnerability of fields to erosion and decreases water infiltration, leading to waterlogging and reduced crop yields.
In drier regions, excessive tilling breaks down the soil aggregates, exacerbating soil erosion by wind.
The loosened soil particles become more susceptible to being blown away, causing land degradation and desertification.
This is a huge concern in regions like the sub-Saharan Africa dependent on agriculture, where soil degradation is a huge concern.
The United Nations Convention to Combat Desertification emphasises preventing soil degradation through sustainable land management practices.
This includes adopting conservation agriculture, ecosystem-based approaches, and integrated water management. Policy and institutional support are vital for incorporating soil degradation prevention measures into national strategies and plans.
Erosion
Excessive tillage practices contribute to soil erosion, diminishing the soil's capacity to support plant life.
Over time, repeated tilling leads to the formation of plow pans, which are compacted layers of soil. Plow pans restrict root growth, reduce water infiltration and increase runoff, amplifying erosion risks.
In sloped areas, aggressive tilling without adequate erosion control measures results in gully erosion. Gullies are deep channels formed by water runoff and they carry away significant amounts of topsoil, nutrients and organic matter.
The protective layering that naturally guards against erosion is compromised by upending the soil through aggressive cultivation.
As a result, the soil becomes susceptible to being carried away by wind or water, leading to substantial soil loss. Not only does this erosion deplete the topsoil of its crucial nutrients and organic matter, but it also poses a threat to overall soil fertility.
Nutrient loss
Aggressive tillage practices accelerate nutrient depletion from the soil, which hampers sustainable agriculture.
The practice also disrupts the natural structure of the soil, affecting its ability to retain moisture and nutrients.
It also harms soil organisms, including beneficial microbes, worms, and insects, crucial in nutrient cycling and maintaining soil health.
Continuous plowing of the soil enhances nutrient leaching, especially in areas with sandy soils.
As water infiltrates the soil, it carries away essential nutrients like nitrogen and potassium, making them unavailable for plant uptake.
Tilling disrupts the natural decomposition of organic matter, which is crucial for nutrient release and soil fertility.
Excessive tillage breaks down organic matter more rapidly than it can be replenished, resulting in a decline in soil organic carbon and nutrient content over time.
Enhanced greenhouse gas emissions
Furthermore, excessive tillage exacerbates climate change by contributing to greenhouse gas emissions.
Disturbing the soil interrupts the vital carbon sequestration process, which involves absorbing and storing carbon dioxide (CO2) by plants and micro-organisms within the soil.
When the soil is continually tilled, this natural carbon sink is disturbed, releasing significant amounts of CO2 into the atmosphere. Additionally, the exposure of soil organic matter to oxygen during tillage triggers a process called mineralisation.
This process releases other greenhouse gases, such as nitrous oxide, further intensifying the greenhouse effect and global warming.
The disruption of soil structure through intensive tillage increases soil aeration, accelerating the decomposition of organic matter.
As organic matter decomposes, carbon is released into the atmosphere as carbon dioxide, a potent greenhouse gas.
High-intensity tillage methods like plowing bury crop residues deeper into the soil, limiting their exposure to oxygen. This leads to anaerobic conditions, causing the breakdown of organic matter to produce methane, another potent greenhouse gas.
Water scarcity
Excessive tillage practices have a notable impact on water scarcity, particularly in regions where water resources are already limited.
It mechanically disrupts the natural soil structure and breaks up clumps, increasing soil surface exposure.
This exposure accelerates water evaporation as more water molecules escape into the atmosphere.
Consequently, this heightened evaporation rate reduces the water available in the soil for plant uptake, leading to water scarcity.
Excessive tillage negatively impacts the soil's ability to retain water.
The disturbance caused by frequent and aggressive tilling breaks down soil aggregates, reducing the soil's capacity to hold moisture.
This reduction in water retention leads to faster drainage and decreased crop availability.
In most regions of Africa, where prolonged dry spells follow heavy rainfall.
Excessive tillage disrupts the soil structure, reducing its ability to retain water during the rainy season.
Consequently, the water rapidly drains away, leaving the soil dry and exacerbating water scarcity during subsequent dry periods.
Way forward
This commentary's purpose is not to push farmers to change their methods overnight but to help them make informed decisions and why they should consider them. Of course, tillage yields certain benefits when employed with discretion and purpose.
For instance, controlled tillage practices help suppress weed growth and ensure the proper incorporation of organic matter, fostering nutrient cycling and soil replenishment.
However, the excessive and indiscriminate use of tillage threatens climate change mitigation and agricultural sustainability. As we navigate the complexities of agriculture and its impact on the environment, striking a balance becomes imperative. Conservation agriculture techniques that minimise or eliminate excessive tillage are increasingly being embraced.
By adopting alternative methods like minimum tillage, no-till farming and implementing cover crops, farmers mitigate soil erosion, reduce greenhouse gas emissions, enhance soil health and ensure the long-term sustainability of agriculture in the face of climate change.
- Takudzwanashe Mundenga is an NSERC-CREATE Climate Smart Soils fellow and MSc candidate in capacity development and extension at the University of Guelph, Canada. His expertise lies in climate change and soil science communications.
