Enhancing Plant Nutrients with Microbes


woman wearing gloves touching grass

Scientist are looking for ways to produce a regular source of food on the moon. You can not just plant crops in a greenhouse on the moon and expect them to grow. They need nutrients that recycle and are in the right form. That takes microbes. Understanding what microbes make nutrients plant available may also allow “earth” farmers to use less commercial fertilizer. Farmers are now using biofertilizers (microbes) to enhance plant nutrition. Here’s a summary of important plant microbes used to make plant available nutrients.

For nitrogen (N), the rhizobium bacteria convert atmospheric N2 into ammonia (NH3). The rhizobia (R) infect the plant in root nodules and then convert N into useable plant forms. Farmers inoculate soybeans, hay, and cover crops with specific rhizobia strains to generate free N for the plant. Use Bradyrhizobium japonicum for soybeans; R. trifolii for red clover, crimson clover, and white clover; R meliloti for alfalfa; and R. leguminosarum for peas, beans, and true vetches. Each legume plant needs a specific rhizobium species for optimal plant growth.

For phosphorus (P), there are several solubilizing bacteria species. Many are Bacillus (B) bacteria like B. mucilainsus, B. megaterium and Psedudomonas fluorescens. If a farmer is getting a soil health test, look for these specific species. These three species are being studied to make P available on the moon. These microbes also need oxygen, water, and soil organic matter (SOM) along with other nutrients. Also, the mycorrhizae fungi (MF) are involved in transporting P and making P plant available. However, these MF fungi mainly use bacteria to make the P plant available by feeding them plant sugars.

Another big plant element is potassium (K). Most soils have lots of K but most of it is tied up in rock formations like muscovite, mica, feldspar, biotite, and illite. Potassium (K) solubilizing bacteria (KSB) convert insoluble K to plant available K. Acidothiobacillus ferrooxidans make both potassium and iron (Fe) plant available. Other Bacillus (B.) species like B. mucilaginous, B. edaphicus, and B. circulans are good bacteria species that make your soil potassium (K) plant available.

N-P-K are the three primary nutrients while calcium (Ca), magnesium (Mg) and sulfur (S) are the secondary plant nutrients needed the most. Calcium (Ca) soil levels are influenced by soil pH, soil type, and the concentration of other soil nutrient. Most Mg comes from plant residues, compost, manure, biosolids and dolomitic lime. Magnesium is one of the least understood soil elements. Recent research shows that MF fungi make Mg plant available but the mechanism is poorly understood. Mg is needed to make chlorophyll but too much Mg makes soils hard. Plant available or exchangeable Mg is more available at low soil pH. For sulfur (S), soils need plenty of oxygen and thiobacillus thioxidans to make S plant available. However, this process tends to produce sulfuric acid which lowers your soil pH. Most microbes create a “micro” environment where they can lower the soil pH in a small area or zone to extract nutrients from mineral sources that not plant available. Plants roots grow best when the overall soil pH is cloerer to 7.

For the micro nutrients like zinc (Zn), manganese (Mn), and copper (Cu), there are several key microbes. Zinc use Pseudomonas protegens, B megaterium, and B altitudinis. (The B. stands for Bacillus bacteria). Zinc activates over 300 plant enzymes and a lack of Zn may cause up to 30% declines in crop yield if it is lacking. Manganese (Mn) solubilizing bacteria (MSB) include many Bacillus (B.) species. There are many strains but some are much better than others at making Mn plant available. Copper (Cu) is a natural fungicide. Copper resistant bacteria like Pseudomonas BGS6 and Endophytic enterbacter sp K3-2 have been studied which makes Cu more plant available.

The soil environment is important for making nutrients available. Generally, soils that are fluffy, friable and well aerated with adequate SOM produce the highest amount of plant available nutrients. When it rains, the water can get into the soil, creating zones where the microbes can do their work. Fluctuating zones of oxygen and water creates an ideal environment where microbes, both aerobic (oxygen loving) and anerobic (low oxygen) microbes can flourish for short periods of time, like an on/off switch. This allows nutrients to become plant available for a short period of time before they become tied up again. High levels of SOM store plant nutrients for later use. Small root hairs can access these nutrients quickly before they are either leached away or tied up. It’s a delicate soil balance greatly enhanced by good soil health!