Home Systems biology Hoorman: Biological nitrogen buffer | Local farm

Hoorman: Biological nitrogen buffer | Local farm

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As crop prices increase, fertilizer prices usually increase as well. Farmers who reserve nitrogen (N) for next year pay at least twice as much. Nitrogen use efficiency is critical as farmers try to reduce nitrogen use while trying to maintain crop yields. The accumulation of soil organic matter (SOM) and improvement of soil health improves the efficiency of nitrogen use.

Soil health and regenerative agriculture systems develop healthy soils with robust microbial communities that efficiently recycle soil nutrients to meet a crop’s nutritional needs. In healthy systems, photosynthesis is maximized, which produces large volumes of soil carbon as a food source for soil biology. Soil biology then recycles these nutrients from the soil to the plant as nutrients available to the plant. Keeping soils rich in SOM or carbon is a key factor in buffering nitrogen and keeping it available to the plant (Larry Phelan).

Inorganic nitrogen fertilizers are usually applied as salts which can damage plants. “Inorganic” means that it does not contain a carbon source while organic means that the N is attached to the carbon. “Salts” are simply positive and negative charges. Nitrate (NO3-) is a negative ion and ammonium (NH4 +) is a positive ion. Adding carbon or increasing SOM is a way to buffer salts and reduce damage to plants while increasing nitrogen use efficiency.

Adding too many inorganic nitrogen salts to a soil can inhibit the soil microbial community. The lower your SOM or soil carbon, the soil has less biological buffer which can then damage both microbial communities and plant growth. In pristine soils or soils rich in organic carbon, this is not a problem. However, with sandy soils, low carbon soils, or soils that have lost a large part of their carbon, salt damage or inefficient nitrogen use becomes a problem. In most of our soils, we still have enough carbon to buffer the soil, but high nitrogen fluctuations and excessive nitrogen release hamper our nitrogen use efficiency.

In a conventional system, farmers often put in soluble inorganic nitrogen in early spring without much carbon. Without carbon to buffer salts, huge fluctuations in available N initially occur, then N decreases during the growing season. Most crops need their maximum nitrogen after pollination, so nitrogen use efficiency is rather low. Soluble nitrogen can be lost in conventional low carbon systems through leaching, causing hypoxia in the Gulf of Mexico or Lake Erie.

Healthy soil microbes take up large amounts of applied nutrients, recycling these nutrients back into their cells, and then release them over a longer period of time. As soil microbes die off and soil organisms feed on these microbes, N mineralization occurs, releasing N in a form available to plants. In healthy soils there is a more constant supply of N throughout the growing season and more N available when the crop needs it after pollination. This improves the efficiency of nitrogen use and is better for the environment.

Not all forms of N are created equal. Plants take up amino acids, proteins and microbial metabolites directly from soil microbes in highly energy efficient forms. The second most efficient form of N is urea, or amino nitrogen, the third is ammonium, with nitrate being the least efficient form of N. When a maize crop absorbs 80% of its needs in N in the form of nitrate, it requires 16% of the total of a plant. photosynthetic energy just for the conversion of nitrate (Marschner) and requires three times more water to convert nitrate to amino acids compared to ammonium. Applying N in a form that microbes can easily use and recycle creates the most efficient use of N (John Kemp).

Instead of trying to feed the plants directly, feed the germs first. The microbial forms of N are not leachable and are available to plants even when there is less water in the soil profile. Apply N as liquid 32-0-0, liquid 28-0-0, or liquid urea 21-0-0 (the most efficient source of liquid nitrogen), then give the microbes what they need to quickly consume the applied nitrogen.

A good recipe next spring is to add 3% of the total nitrogen solution as humic acid (based on weight or volume). Then add ammonium thiosulfate (ATS) 12-0-0-26S to produce a nitrogen / sulfur ratio of 10: 1 in the final solution. Then add a source of carbohydrate or sugar such as molasses to 3% of the total solution. Finally, add molybdenum, which is necessary for the nitrate reductase enzyme to convert N to vegetable proteins. Efficient nitrogen use is essential to achieve good yields and higher profits while protecting the environment.


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