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Conservation agriculture (CA) is considered a sustainable practice with the potential to maintain or increase crop productivity and improve environmental quality and ecosystem services. It typically improves soil quality and water conservation; however, its effect on crop productivity is highly variable and dependent on local conditions/management. Crop residue retention plays a crucial role in CA and can help to improve overall soil health and ultimately crop productivity and sustainability.
2. CA has been delivering positive results on improving soil water conservation
3. Conservation Agriculture and Water: From Erosion to Eutrophication
4. Conservation Agriculture and Greenhouse Gas Emissions: Decoding the Complexities
Crop and soil management practices affect the release as well as capture of greenhouse gases (GHGs) from the soil to the atmosphere and vice-versa . Consequently, agriculture has been identified as one of the four important sectors that could contribute to reducing global GHGs emissions . The reduction in fuel usage associated with the smaller number of tillage operations under CA is well established to reduce GHGs emissions. For example, fossil fuel emissions from agricultural operations under conventional tillage (moldboard plough) were estimated to be 0.05 Mg ha −1 yr −1 compared to 0.03 Mg ha −1 yr −1 under no-till conditions .
In addition to C change, CA can also affect the flux of other GHGs, particularly methane (CH 4) and nitrous oxide (N 2O). Similar to C storage, CA has been observed to both increase and decrease N 2O emissions, depending on the influence it has on soil moisture and microbial activities and, thus, nitrification and denitrification. For example, where CA increases soil moisture, microbial biomass, and labile carbon, there is potential for greater rates of nitrification and denitrification and thus N 2O emission . However, when CA lowers soil temperatures, and improves soil structure and drainage, denitrification and N 2O emissions can decrease . Less information is available regarding the impact of CA on CH 4 emissions; however, these are commonly observed to either remain unchanged or decrease due to improvements in aggregate stability/porosity and the subsequent uptake of CH 4 by methanotrophic bacteria .
Overall, it is the net impact that CA has on CO 2, CH 4 and N 2O flux that determines whether a CA system will act as a net sink or source of GHGs. However, relatively few studies consider the flux of all GHGs from the soil concurrently. One meta-analysis that summarized the results of nine studies conducted globally reported an average difference in global warming potential (GWP) of −2.39 Mg ha −1 yr −1 in NT compared to conventionally tilled systems when considering both soil GHGs flux and emissions from farm operations . However, a second analysis noted greater GHGs emissions from the soil of NT compared to conventional systems during the first 5 years of practice (GWP of +0.39 and +1.51 Mg ha −1 yr −1 in humid and dry temperate regions, respectively), but lower or similar emissions after 20 years ( GWP −2.07 and −0.36 Mg ha −1 yr −1 in humid and dry temperate regions, respectively) . The decline in GHG emissions in NT systems over time was largely due to declines in N 2O emissions, which have been found to reduce as soil aggregation and drainage improve in more established NT systems .
5. Can Conservation Agriculture Really Conserve Soil Biodiversity?
As CA promotes the accumulation of soil organic carbon at the surface of the profile, it is expected that the microbial activity and biomass must be higher in CA farms due to the increased availability of organic substrates . The improvements in soil aggregation, aeration and moisture availability also create favorable conditions for increases in both the size and diversity of microbial populations, as can crop diversification through crop rotation or intercropping . Full implementation of CA components has been reported to increase the diversity of both fungal and bacterial populations , with NT in particular favoring the increase in fungal diversity due to the absence of tillage . The increase in microbial diversity has several significant implications for crop productivity and soil health. For example, several plant growth-promoting soil microbes proliferate in these favorable conditions and contribute to enhanced plant growth, disease suppression and abiotic stress tolerance . Microbial-induced enzymes associated with nutrient cycling are also found in greater amounts under CA, leading to higher nutrient availability under CA .
CA has the potential to not only improve microbial diversity but also to influence such soil macro-fauna as earthworms, ants, termites and beetles . These macro-fauna improve soil health by breaking down plant residues, increasing macroporosity, and improving water infiltration, soil aggregation and nutrient cycling . Intensive tillage practices often kill or disturb the functions of soil macro-fauna, exposing them to the soil surface and other predators. This loss of soil biodiversity severely affects the soil physico-chemical properties and ultimately influences crop productivity. Therefore, biological parameters are often used as indices in characterization of CA soils. The significant effects of CA on soil macro-fauna could be greater in warm temperate zones and soils with higher clay content (>30%) and low soil pH (<5.5) .
The entry is from 10.3390/agriculture11080718
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