Nutrient purchase tends to be one of the larger expenses on most farms. Plants respond to soil fertility, whether it is added as a chemical fertilizer, organic source, or provided through livestock. Nutrients will be taken up by growing plants. When they are in the proper balance, they will work together to grow plants efficiently. By creating an imbalance of soil fertility, plants do not grow as they should. They become too tall or too late for example, which will influence the yield at the end of the season. By creating a balanced food source for the soil biology, nutrients will be allowed to cycle through the plantsoil relationship. There will be leaks from the system, namely what is harvested and taken off the field.
Nitrogen is something that should rarely have to be purchased. In the atmosphere, there is 78% nitrogen, and there are legume plants that grow here that can capture the atmospheric nitrogen and make it available to the soil biology and other plants. By utilizing legumes in the rotation, the nitrogen required to be purchased can be at least subsidized, if not eliminated completely. By including deep rooted species, any nitrogen trying to escape through leaching can be repositioned back to the root zone. Having a combination of wide and narrow carbon:nitrogen ratio residues will allow a slower release of nitrogen as it rots, allowing a lower level of nitrogen available throughout the whole growing season instead of front loading the full year’s amount as seeding. As Patrick Fabian from Fabian Seed Farms says, “we eat three meals a day, morning, noon and late afternoon. Plants work better when they are fed the same way. Why should we give our plants all three meals at breakfast?” By spreading out our nitrogen feeding, there will be less issues like lodging, excessive plant height, disease, and unnatural maturity. Plus there is the management side. If growing conditions are poor, the nutrients are not needed or added, whereas if growing conditions are optimal, keep feeding the plants. Phosphate is a trickier nutrient to manage. There is a relatively large amount of phosphate in most of our soils, but is in a nonexchangeable form, namely stuck in a calcium phosphate bond. The exchangeable portion of phosphate is very immobile so the main way plant roots take up phosphate is actually root interception, where it has to hit it. The trick is making it available.
Increasing the mycorrhizae population in the soil is one way to help increase the uptake of soil phosphate. Mycorrhizae are able to get into parts of the soil that roots can not get into, so they are able to access more of the soil aggregates. The keys are there needs to be good populations of mycorrhizae and the plant needs to be a host for mycorrhizae.
Another strategy is to utilize more tuber crops in cover crops. Tuber crops, like turnip and radish, will accumulate phosphate in the tuber. From research supplied by Cover Crop Solutions, radish plants will accumulate twelve pounds of phosphate per tonne of growth. Turnips would act similarly. By allowing the tubers to grow, and then rot back to the soil, it will build the exchangeable phosphate levels.
Livestock grazing is the quickest way to boost phosphate levels in the soil. Over 90% of phosphate passes through cattle and is deposited as an exchangeable form of phosphate. After corn grazing for three years and only using moderate fertilizer in year one, there is enough phosphate to grow three grain crops without adding any, then to grow a five dry tonne corn crop to be grazed again. By rotating livestock grazing on different land will help build nutrients, especially phosphate. Potassium is the other nutrient that can be managed. The biggest loss of potassium comes from baling straw. By returning straw to the soil is a big step in maintaining potassium levels in the soil. If no potassium fertilizer is added, it can be replaced by green manuring or growing tuber crops. Research supplied by Cover Crop Solutions show just over 100 pounds of potassium per tonne of dry biomass.
The end result of having roots alive in the soil throughout the frost free growing season is the roots have more time to drive deeper into the soil to gather more nutrients, bringing them back into the annual crop rooting zone. This then drives greater biomass of both roots and shoots, stimulating a greater microbial population, driving soil biology, and building organic matter.
If there is a nutrient deficiency, the process is slowed down. The amount of slow down will be determined on how critical the nutrient is to plant growth. A soil test will give some indication of issues, but tissue tests will determine what the plant is able to take up. Most soil tests are a snap shot of what is available in the soil at that time. A tissue test shows what the plant was able to take up while growing. Most of the soil tests will have some estimated nutrient release built into them using some research data to match what may happen in the soil. The estimated nutrient release is influenced by growing conditions, moisture, and quality of organic matter. Low quality organic matter will not supply as much nutrients as higher quality
organic matter. Nutrient tie up in the soil can occur for a few reasons, such as salinity, soil aggregation, nutrient interference, slow release, dry soil, poor rooting system, low mycorrhizal populations, and cold soils.
When starting into cover crops and soil improvement, there is a urge to start cutting back on applied fertilizer, either chemical fertilizer or organic amendments. There is a lag between the start of recovery and the point where inputs can be reduced. Nutrient cycles have to catch up to the new management systems, even though it is more like nature. Strip trials of reduced inputs are necessary to see how the soil and the soil ecology is going to react to it. Using tests like Solvita gives an indication of how the soil biology is growing and shows how much is active. It is similar to taking your pulse while exercising.
Nutrient balance is important, especially for micronutrients. If doing a trial with copper on wheat, and the potassium levels are low, the copper will not show a benefit. There may be a grain quality improvement, but not much for yield. On the other hand, having over application of nitrogen will create more issues of lodging, masking true maturity, and create internal plant imbalances.
The Mulder’s Cycle is an important chart to keep in mind when managing nutrient application. Green manures will take most of the soil nutrient interactions out of play because most plants take up most nutrients in the quantity they require. There are instances of luxury uptake, or taking up more than what the plant requires, like nitrogen. By reading the chart, by when nitrogen is added, the magnesium is increased in availability while boron and potassium are negatively affected. This stresses how important nutrient balance is, plus it shows how adding one nutrient may affect another.