Biological Life in the Soil
This entry covers some of the biological processes within soil, affected by biological and fungal activity. These processes affect the health of plants, and determine whether the soil hosts biological activity that is beneficial for plant growth.
Bacteria perform many functions within the soil, and help plants access nutrients. Their activity can support plant function, as well as tarnish it due to non-desirable pathogens.
What is Chemotaxis?
It is the movement of an organism in response to a chemical stimulus using cellular communication.
Bacteria emit biochemicals that act as communication molecules to encourage microbes to move away from dangerous environments. This causes an intentional movement of plant roots toward or away from a chemical stimulus.
This includes…
-Hormonal secretions for plant growth, maturity, and reproduction
-Biochemical defense compounds against fungal, bacterial, insect, and nematode enemies
-Compounds solubilizing certain tied-up nutrients like iron, phosphate, manganese etc. -Providing microbial secretion to enhance microbial growth and activity, providing enzymes that can decontaminate miscellaneous toxins.
Microbial systems make up 50 percent of the Earth’s total biomass and 80 percent of all the Earth’s biodiversity is microbial.
Soil hosts 2-3 million species of bacteria, 1.5 million species of fungi
Bacteria have tremendous reproduction potential
These are practices used to encourage healthy bacteria and prevent disease in your soils
-Limiting acid soils
-Compost
-Proper irrigation and water quality (pH, TDS, bicarbonate, alkalinity, salinity)
-Aeration and drainage
-Reduced or zero tillage
-Cover crops -multiple species
-Balanced fertilizer applications
-Tight crop rotations
-Crop residues returned to surface or shallow sheet composting
-Seed inoculation with mycorrhizal and trichodermal fungal spores
Carbon and Oxygen in soils
Air vs. Soil – Oxygen/Carbon percentages
Atmosphere-21% oxygen, .025-.035 % carbon
Soil atmosphere- 15% oxygen .2-.4 % carbon
Carbon dioxide is a primary raw material that plants recycle through their stomata to create sugars, which are in turn the building blocks of numerous other carbon complexes, such as starches, cellulose, hemicellulose, lignin, waxes, oils, resins, pectins, fructans, glucans, and numerous plant secondary metabolites like terpenes alkaloids and phenols.
Climate change issue– vast amounts of carbon lost from our soils and the soil ecosystems diminish the ability to rapidly and effectively sequester carbon dioxide. Soil erosion exceeds 24 billion tons per year worldwide.
Increasing the soil organic matter on the planets 4.9 billion hectares of rangeland by 2 percent would sequester 2880 billion tons of co2 compared to 44 billion tons emitted by human activities per year.
Facultative Organisms- those that can adapt to utilizing oxygen either as atmospheric oxygen or as a complex oxygen compound such as no3 or so4.
Manure lagoons are challenged by depleted oxygen. They can be mixed with equipment or clay added to cow food or lagoon.
Water and Irrigation
Evaporation of water in the soil is often due to lack of vegetative cover, and organic matter.
Varying soils have different water holding capacities.
Example
Sandy soil can hold 8 percent water
Silty loam can hold 28 percent
Cover crops reduce runoff
Clay and organic matter contain more pores and surface area
Water content and evaporation is affected by Soil temperature
Soil temperature is determined by…
-Field slope
-Season
-Rainfall, irrigation
-Wind speed
-Humidity
-Cloudiness
-Ground cover
-Amount of tillage and soil disturbance
-Soil structure and permeability
-Soil density
Comprehensive soil testing
Ward Laboratories– Provides in depth biological information called green chemistry. Includes the Solvita 24 hour Co2 Burst test to evaluate the respiration of the soils microbes. Measures carbon dioxide released in a soil sample. Water extract taken to determine the water-extractable organic carbon and water-extractable organic nitrogen. Measures the quality of carbon, and energy source that feeds on soil microbes. Organic pool of carbon is roughly eighty times smaller than the total carbon amount. Water extract of the soil is taken to determine total nitrogen, inorganic nitrogen and organic nitrogen.
Organic nitrogen– Protoplasm-it consists of amino acids, peptides, algae, nematodes, and plant cells. Easily digested by living microbes and released to growing plants while not at risk of leaching.
Organic carbon to nitrogen ratio
- Determined using the water extracts of each (carbon to nitrogen)Soil ratio above 20:1 indicates that no net nitrogen or phosphorus mineralization will occur, meaning nitrogen and phosphorous are “tied up” within the microbial biomass until the ratio falls below 20:1.
Phospholipid fatty acid test (PLFA) analysis– measures functional groups of microbes and their contribution to the total biomass in the soil, both in weight and percentage. Community composition ratios are evaluated for fungi to bacteria ratios scaled from very poor to excellent. Bacteria are important but fungi populations are indicators of soil health.
Parasitic Nematodes –
These are aquatic animals, that need moisture to migrate. They are .5- 4.0 millimeters in length. Parasites can attack all parts of the plant. They utilize an organ called a stylet, which is a spear-like form used to puncture plant tissue and withdraw liquid contents.
Ectoparasites- Remain outside of the plant tissue. Have short stylets and can only feed on epidermal tissue of the roots.
Endoparasites- Dwell inside the root mass and cause more damage to the plant. Incidence of nematode infestation in agriculture soils is directly related to the health and complexity of the soils ecological community.
Anything that compromises the size of the root mass amplifies the negative effects of nematode infestation. Sandy or sandy loam soils low in humus and dosed with salt fertilizers, pesticides, and irrigation water are ideal environments for parasitic nematodes.
Signs of nematode dominance- patches of wilting, dying, clorosis, early senescence, stunted growth, and thinning.
Accurate assessment of nematode problem only determined by a nematode lab assay to provide identification of the species, and the numbers present.
Same symptoms caused by nematodes can be attributed to poor soil health and extremes in moisture content.
Addressing nematode infestation
-Crop rotation, not returning a crop to the same plot for at least 3 years.
-Cover crops, cocktails of at least four to six species
-Vegetative fumigants such as plants of the mustard family (crucifers like kale, cabbage, collards, broccoli) note. When using crucifers to fumigate soils, ensure that a non-cruciferous crop is planted afterward and properly inoculated with mycorrhizae as well as rhizobium.
-Quality compost- introduces a plethora of healthy bacterial, fungal, and predatory nematode species into the soil. Pest suppressing metabolites are found in compost.
Using iodine to kill nematodes- alcohol in solution becomes phytotoxic. Tame solutions without alcohol helpful for killing nematodes in root bulbs acting as a bacterial enhancer especially of nitrogen fixing rhizobia, and azotobacter.