Nitrogen (N) is the most widely used and needed nutrient. Plants are surrounded by nitrogen in our atmosphere, but unfortunately, this N is not available in a form that plants can use to grow, develop, and reproduce. Despite nitrogen being one of the most abundant elements on earth, N deficiency is probably the most common nutritional problem affecting plants.
Healthy plants often contain 3-4% nitrogen in their aboveground tissues. These percentages are much higher than those of any other nutrient—except carbon, hydrogen, and oxygen—which are supplied to us free from air and water.
Nitrogen is an important component of many structural, genetic and metabolic compounds in plant cells. It is a major component of chlorophyll, the compound needed for photosynthesis. Nitrogen is also a major component of amino acids, the building blocks of proteins. Finally, nitrogen is a significant component of DNA. Without nitrogen, there would be no life as we know it.
There are two main sources of nitrogen: N-containing minerals in our soil and the vast amount of N in the atmosphere. The nitrogen in soil minerals is released as the mineral decomposes. This process is quite slow and contributes only slightly to N nutrition in most soils. Most of the N needs of the plant have to be met by the addition of commercial fertilizer.
Nitrogen fertilizers are produced when atmospheric nitrogen is chemically fixed to hydrogen to form ammonia (NH3). Although the supply of N from the air is virtually infinite, the sources of hydrogen are limited. Almost all modern ammonia production facilities use natural gas as the hydrogen source, which is the major cost of nitrogen fertilizer production.
Most plants take in nitrogen continuously throughout their lives, and N demand usually increases as plant size increases. Providing adequate N allows an annual crop, such as corn, to grow to full maturity, rather than delaying it. A nitrogen-deficient plant is generally small and pale green or yellowish. Older leaves often become necrotic and die as the plant moves N from less important older leaves to more important younger ones.
All crops need adequate supplies of nitrogen. Fortunately, properly nodulated legumes produce most of the N they need. However, all the other crops we grow need sufficient additional nitrogen for maximum production.
So how much nitrogen do we need? Well, for example, a 150 bu/A corn crop removes 135 lbs. of N in the grain. However, we need to supply about 180 lbs. of N to allow for the N in the grain and plant residue as well. So we need roughly 1.2 lbs. of N per bushel of expected yield. Wheat needs about 2.5 lbs. of N per bushel. After we calculate crop needs, we can subtract off soil test values, manure credits, and previous crop credits.
The most profitable rate of nitrogen to apply will vary based on previous cropping history, geographic location, realistic yield goals, manure applications, crop being grown and more. Don’t be misled into dropping the rate of applied nitrogen simply because the price of nitrogen has risen. The price of grain and the price of nitrogen have only a minimal effect on the most profitable rate of nitrogen to apply.
For example, let’s say N costs increase $6 per acre this year. But suppose you decide to pass on the $6 per acre added cost and reduce N applied by 20 lbs. If yields plunge 15 bu/A, at $2.75 per bu. corn you lose more than $40 per acre trying to save $6 in input costs.
Need help with the calculations? Give us a call.
Nitrogen is just one component in a well-balanced fertility program. Other macro and micronutrients are extremely important to growing a profitable crop. Economic optimum rates of nitrogen, when tied in with an overall sound crop production plan, result in crops that are productive and competitive against pressure and stress exerted from weeds, insects, weather, and more.
Remember, fertilizer is a worthwhile investment. While fertilizer prices have risen, fertilizer prices are relatively low when compared to the increases in prices of other crop inputs, such as seed, labor, and machinery. Using fertilizer at recommended rates is profitable. Always fertilize for optimum yields.