How and Why Conservation Agriculture Works

To better understand how and why the system works to enhance and sustain agricultural production while conserving natural resources, we should consider each of the essential features of conservation agriculture one by one. These include:

  • Maintaining permanent or semi-permanent soil cover. Plants are left growing or killed and their residues left to decompose in situ. The primary function of this is to protect organic matter-enriched topsoil against chemical and physical weathering. Plant residues intercept energy from falling raindrops, provide a barrier from strong winds, and moderate temperatures, improving water infiltration and decreasing surface evaporation from sunlight. Surface cover also favors enhanced levels of biological activity by providing food for soil microbes, especially in tropical and sub-tropical areas.
  • Minimum soil disturbance. No-till (NT/ZT) does not involve any loosening of the soil except for a very small area immediately surrounding where the seed is planted. This lack of soil disturbance serves to maintain overall soil structure,including aggregate stability, porosity, and biotic channels both of which promote the exchange of water and gases, improve infiltration of water, and provide habitat to an abundant and diverse population of soil biota that are not disturbed.
  • Regular crop rotations. Well-balanced crop rotations can neutralize many of the pest, weed, and disease problems associated with not tilling the soil, including the proliferation of insect pests, harmful bacteria, viruses, fungi, and other microbes by increasing the diversity and abundance of beneficial soil biota that can help keep pest and disease problems in check. Rotating crops also interrupts the life cycle of many weeds, thereby leading to a reduction in overall weed growth. These benefits translate to a typical yield increase of about 10 percent of crops grown in rotation, as compared to those grown in monoculture. Note rotation needs to remain in the pillars of CA for the above reasons and not substituted with the term “Diversification” that has crept into the recent literature. Of course, CA as a whole improves soil organism diversity.
  • Utilization of green manures/cover crops (GMCC's). Cover crops are grown specifically to help maintain soil fertility and productivity. GMCC's increase soil organic matter (SOM) levels in at least one of two ways - by decreasing erosion and/or by adding fresh plant residues to the soil. Leguminous cover crops offer the added advantage of being able to fix nitrogen from the atmosphere and add it to the soil, thereby increasing overall nitrogen availability for other crops. Cover crops are usually mowed, sprayed with chemical herbicides, or otherwise killed by frost before or during soil preparation for the next economic crop. It is generally recommended that you leave a week or two between the killing of the cover crop and the planting of a primary crop in order to allow for some decomposition to occur as well as to lessen the effects of nitrogen immobilization and allelopathic effects. Note that in many sub-tropical and tropical intensive systems, there is not always time or space to grow a cover crop, but the multiple crops grown will provide useful residues if left on the soil surface.
  • No burning of crop residues. Since crop residues are the principal element of permanent soil cover, they must never be burned or otherwise removed from the soil surface. Rather, plant residues are left on the soil surface in order to protect organic matter enriched topsoil from erosion while also adding fresh organic matter upon decomposition. Burning not only creates significant air pollution but also dramatically increases mineralization rates, leading to the rapid depletion of soil organic matter and nutrients from the soil. However, in some situations farmers need to think of the tradeoff between removing residues to feed their animals and leaving them to feed the soil. A win-win situation would be to do both as yields and biomass increase over time. Note that burning is a favored farmer practice so residues are not a problem when planting the next crop, but in terms of soil health and also air pollution,it is not a good practice
  • Integrated disease and pest management.¬†Conservation agriculture depends heavily on enhanced biological activity to help control insect pests and other disease causing soil organisms. Integrated pest management (IPM) entails the judicious use of crop rotations and other beneficial plant associations as well as chemical pesticides, herbicides and fungicides to control insect pest and disease problems. Over time, the enhanced biological activity and abundance brought on by no-till and other CA technologies often result in decreased applications of agrochemicals and reduction of chemical fertilizers as nutrient cycling from soil biota improves.

  • Reduction in fossil fuel use and greenhouse gas (GHG) emissions. Compared to conventional tillage, which often requires several tractor passes in a typical growing season, no-till significantly reduces the use of tractors and other heavy farm machinery and thus diesel, leading to less greenhouse gas emissions and costs to farmers for fuel and wear and tear of tractors. Furthermore, the increased levels of soil organic matter (SOM) and plant-available nitrogen typically found in CA soils as a result of reducing the oxidation of organic matter with tillage greatly reduces the quantity of chemical fertilizers farmers apply, many of which require significant fossil fuel energy to process. Thus, overall fossil fuel use and greenhouse gas emissions are greatly reduced.
  • Controlled / limited human and mechanical traffic over agricultural soil. As mentioned above, the number of tractor passes over a given field is significantly reduced under CA, as compared to conventional tillage systems. However, increased bulk densities have been reported under CA, though this can be corrected by limiting the use of heavy farm machinery when soils are wet and most prone to compaction and/or by converting to a permanent raised bed system. Multiple passes of tractors or even animals used for tillage can result in plow pans that restrict drainage. No-till is less likely to form plow pans especially if controlled traffic systems are used when seeding.

 

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