An organic farmer once told me the difference between his organic soil and conventional soils is that his soil is ‘alive’, clumps and is moist, and not dry dust. You may remember plants you purchased in a store with horrible soil that was like styrofoam – this is soil at its worst. Healthy soils contain good organic matter, diverse microbial communities, and appropriate chemical/physical composition (e.g., a balanced pH, minimal toxic chemicals). Soil organic matter enables soils to clump and absorb and hold moisture better. Healthy soils serve to filter pollutants and chemicals and microbes can help detoxify toxic chemicals. These positive effects enable healthy soils to better withstand environmental extremes of droughts, floods and temperature fluctuations expected by climate change. Also, diversifying and rotating crops can break overwintering diseases (Khan et al., 2024). To farmers, diversified crops and improved soils offer food security, soil sustainability and economic stability.
Organic soils require macronutrients: nitrogen, phosphorous and potassium (NPK), the same as conventional. Microorganisms are important in the natural production of nitrates, phosphorous and carbon within soil organic matter. Soils store more carbon than the oceans and atmosphere combined; sequestered carbon is built up in soil organic matter, produced by microbial communities in healthy soils. Microbial activities help in producing soil organic materials but require the right amount of water and an acceptable pH for decomposition and soil carbon sequestration process to occur (Khan et al., 2024). Nitrogen fixing is accomplished by specific microbes, which convert nitrogen in the air to ammonia, while other microbes create nodules that help plants absorb the nitrogen. Nitrifying bacteria turn ammonia into nitrites then nitrates.
Phosphorous is a non-renewable mineral that is currently mined for fertilizer use. However, helpful microbes, bacteria and fungi secrete sufficient acids to dissolve phosphorous bound in minerals within humus (Khan et al., 2024). Innoculants and hormones help make insoluble minerals soluble, improve nutrient uptake, and help plant roots grow. Microbial health and growth depend on soil characteristics, moisture level, soil depth, slope, plants grown, pH, nutrient levels and a low level of heavy metal toxicity.
Organic fertilizers include biochar, manure, fermented grass, compost, vermicomposting, cover crops, biofertilization (adding beneficial microorganisms), mulching and conservation tilling (leaving plant residues in soils) (Khan et al., 2024). These fertilizers must be carefully combined to achieve the NPK nutrient balance. Organic fertilizers release nutrients slowly, because microbes and bacteria process these nutrients to build organic carbon, nitrogen and phosphorous that can be taken up by plants. Organic fertilizers decrease soil acidity, and improve microbial growth, thereby increasing soil organic matter (Khan et al. 2024). Since higher soil acidity increases heavy toxic metals, organic fields would be expected to be lower in these metals. Pesticides are a threat to soil organic matter since they indiscriminately kill microbial and invertebrate life.
Conventional farming raises acidification in soils, and conventional fertilizers can release chemical nutrients quickly, both of which reduces microbial and bacterial soil communities that generate helpful soil organic matter. Conventional farming thus results in greater soil erosion, global warming potential, terrestrial and aquatic toxicity, eutrophication, and acidification (Khan et al. 2024).
Organic farming is not a miracle everywhere with current science. Microorganisms do not do well in hot, dry (arid, semi-arid) temperatures, or in sandy soils that do not hold water or nutrients well (Khan et al. 2024). Organic fertilizers will not do well in acidic or saline soils, where microbes have more difficulty surviving. Finally, even where organic is feasible, a difficult conversion process to organic may take a couple years of lower yields.
References
- Khan, Muhammad Tahir, Jurate Aleinikoviene, and Lina-Marija Butkevicien (2024) Innovative Organic Fertilizers and Cover Crops: Perspectives for Sustainable Agriculture in the Era of Climate Change and Organic Agriculture. Agronomy 2024, 14, 2871:1-29. https://doi.org/10.3390/agronomy14122871