Natural Nitrogen Sources
A week of good weather finally is letting farmers either replant or finish planting. May weather was more like March and April weather while March and early April were warmer than normal. Some crops look good but many are still struggling and stands are quite variable. Wheat looks the best and likes cool wetter weather. Hay is finally started to get made.
Now farmers are turning to spray spraying tweeds and get nitrogen (N) put on corn. With warmer weather, corn should start growing and have a better color. Microbial populations double with every 8-90F in soil temperature. This is good for getting nutrients into the plant and also in helping the plant with its N needs. For corn, N fertilizer prices are really high and corn prices are low, so putting on what N is needed and no more is the most economical.
When N was cheap, the common rate was 1.2# of N per bushel of corn produced. So, for 200-bushel corn, a total N rate of 240# N was advised and for 250 bushel 300# N. With new corn genetics, the rate is closer to 1# per bushel corn or 200-250# total N per acre. Farmers with healthy soils can do it with .7# N or 140#N-175# total N for 200-250 corn bushels. Why?
Accounting for nitrogen (N) in healthy soils just got more interesting! Our old school diagrams on the Nitrogen Cycle are mostly outdated. Old nitrogen cycle diagrams mostly showed inorganic forms of nitrogen (nitrates (NO3-), ammonium (NH4+)) cycling in the soil but now we know that plants can take up organic forms of N in the form of amino acids, peptides, proteins, enzymes, and even hormones. The following is a revised N accounting based on healthy soils.
The atmosphere N (N2) is 78% N in the form of a gas with three covalent bonds. Most microbes cannot utilize this form of N but a few can. Rhizobia are nitrogen fixing bacteria that form mutualistic associations with legumes (beans, peas) and clovers. They form nodules that are anaerobic (lack oxygen, pink inside) where atmospheric N2 gas can be converted to plant available N, mostly ammonium. Soybean need as much as 420# N to produce a good crop, most of which comes from good root nodulation with Rhizobia bacteria. Some legume crops like alfalfa, hairy vetch, Balansa clover, and Austrian winter pea are credited with adding 100-200# N to the soil.
Another source of N is free living bacteria that take atmospheric N2 gas and convert it to plant available N. In a conventional tilled soil, this may only be about 20# N/acre but in a healthy productive soil it can reach 100# of N/acre. Some new biologicals have many gram+ bacteria which make their own N including Lentoactobacillus parakefiri, and Lactiplantbacillus plantarum. Other bacteria like Lacticaseibacillus rhamnosus contributes to the decomposition of plant residues and organic matter, accelerating turnover of carbon and N-P-K to maintain soil fertility.
Over 70 species of protozoa consume microbes and release nutrients especially N. Protozoa consume as many as 10,000 bacteria per day and these bacteria have a C ratio of 5:1 (16.7% N) while Protozoa are 30:1 C or about 3.2% N. When protozoa consume bacteria, the excess N is excreted as Urea (CO(NH2)2 and after some more bacteria conversions are plant absorbed as ammonia (NH3), ammonium (NH4+) or nitrates (NO3-).
A new form of plant N is rhizophagy where whole amino acids (AA), peptides, and proteins are absorbed by the plant from a bacteria called Pseudomonas Pseudomonas are gram-, rod shaped bacteria that live in the rhizosphere. The rhizosphere is that biologically active zone right around the plant root. Plant roots absorb these bacteria with the help of the amino acid arginine. Once inside the plant cell, Pseudomonaslose their protective cell wall, become spherical and feast on the soluble nutrients in the cytoplasm of the plant cells.
As Pseudomonas grow and multiply (4 new cells per one cell division), they excrete whole amino acids, peptides (strings of AA), and full proteins into the cytoplasm to enhance plant growth. As much as 40-60% of all plant N comes from rhizophagy, a process that was unknown just 10 years ago. Pseudomonas expand the root cell wall and are responsible for forming rapidly growing root hairs. They are expelled in waves back to the soil, form new cell walls (become rod shaped) and can enter the root again multiple times, repeating the whole process. Healthy soils need less commercial fertilizer because they have multiple N sources that can be used to make amino acids and whole proteins efficiently to promote optimal plant growth and yield.