Marc Schober is the editor of Farmland Forecast an educational blog devoted to investments in agriculture and farmland.
Maximizing Yields With Fertilizer
May 04, 2011
Just like humans, crops need to be healthy in order to yield their maximum potential. The application of fertilizer helps keep plants strong and healthy by providing nutrients to a plant throughout its life. The three macronutrients that are essential for plant growth, especially in corn, soybeans, and wheat, are nitrogen, phosphorus, and potassium. Micronutrients are also very important in order to obtain high yields, but a much smaller amount by volume is needed in soil.
In order to feed the growing world population, gross crop output needs to increase by 3.4% over the next 10 years, and the primary way to achieve this goal is through higher crop yields. Fertilizers will play a key role in increasing global agricultural output and application rates and demand will be driven by the world’s rising population.
Derived from natural gas, nitrogen is the most widely used fertilizer in agriculture by volume. Grass crops, including corn and wheat, require large amounts of nitrogen to obtain optimal yields. Plants with nitrogen deficiency can often be seen by their yellowing of the inside of their leaves.
There are three different ways that a farmer may chose to apply nitrogen. The first, and most common, is the dry application of urea nitrogen which is 46% nitrogen by weight. Urea is applied through broadcast application, but can convert to ammonia or nitrate in a short amount of time that will evaporate and leech out of the soil. An ample amount of rainfall is needed after urea is applied to be absorbed by the soil, otherwise the farmland will have to be tilled to work the urea into the soil to prevent leeching.
The second type of nitrogen fertilizer is liquid form which is often either 28% or 32% nitrogen by weight. The key difference is freezing temperatures. 32% liquid nitrogen is primarily used in southern states while northern states require 28% liquid nitrogen because its freezing point is lower, but the concentration of nitrogen is also lower. Liquid nitrogen is usually applied by banding it with other chemicals and herbicides to save on diesel costs.
The final form of nitrogen is the gas form; anhydrous ammonia. This gas is dangerous to work with, but anhydrous ammonia is usually cheaper than other nitrogen forms and the gas will not leech out of the soil as much as other forms of nitrogen. If farmers have the opportunity to apply nitrogen in fall, anhydrous ammonia is often the form of choice because it will not disappear by spring.
Crop rotation is taken into consideration when applying nitrogen since certain crops require more nitrogen than others. The more crop residue that is on the soil surface, the more nitrogen is needed to help break down the carbon by promoting bacteria growth. Farmers will need to apply 0.9 lbs of nitrogen per bushel of anticipated corn yield, if corn is planted after a previous soybean season. If corn is planted after a previous corn season, 1.2 lbs of nitrogen per bushel of anticipated corn yield will be required. For example, if 200 bushel per acre corn yield is anticipated for this coming year and the field had soybeans in it last year, 180lbs of nitrogen must be applied per acre.
Critical to the photosynthesis process of plants, phosphorus helps speed up crop maturity and helps overall plant health. Healthy crops will be less susceptible to disease and able to produce optimal yields. The nutrient is surface mined with 80% of the production coming from the U.S., China, Morocco, Russia, and Tunisia.
Phosphorus can be present in two different forms in soil; either available or unavailable. Unavailable phosphorus is phosphorus that is in the soil, but currently bonded to other elements forming compounds that do not allow the phosphorus to be able to be used by plants until the chemical bonds deteriorate. Available phosphorus is unbounded and can be consumed by plants. To create more available phosphorus when applying fertilizer, farmers will often band phosphorus with specific chemicals that bond to the phosphorus, but only temporarily, allowing the element to become available quickly after application.
Phosphorus is applied by either broadcasting solid phosphorus rock on to a field, or injecting it in the soil subsurface. Farmers typically apply phosphorus every two years since the nutrient only moves a couple inches in the soil per year. The mineralization of organic soil matter will also naturally create phosphorus, but typically is not enough to sustain required crop yields. Corn that has low phosphorus levels will often have purple colored leaves and can be seen from a distance.
The third macronutrient that is vital in crop production is potassium, which adds strength to a plant’s stalk and root system. A plant’s internal workings are greatly affected by the amount of potassium that is available to it. Potassium will remain in the soils for up to three years after application.
The growing cost of fertilizer has been taking a toll on U.S. farmland that requires potassium. In a field study conducted by Ag PhD, 40% of northern U.S. farm fields were deficient in potassium in 2004 and 75% were deficient in 2008. Crops deficient in potassium will show yellowing of the outside of the leaves.
Potassium can be applied in two different forms. The dry form, called potash, is broadcast applied but requires a few months to breakdown in to the soil. Farmers often select potash because it consists of potassium and chlorine. Potassium hydroxide, the liquid form, is typically blended with other liquid nutrition and is immediately available for plants growth.
Micronutrients, or trace elements, are essential in crop production however the amount needed for optimum nutrition is very small. Micronutrients are just as important to crop production as the major nutrients because with a deficiency in just one micronutrient, major yield loss can occur.
There are seven primary micronutrients essential to plant growth that include manganese, boron, copper, iron, chlorine, molybdenum, and zinc. The difficult issue is the ratio at which each micronutrient is needed as too much or too little of any micronutrient can hurt yields. Blended micronutrient products have come on the market to help solve this issue of varying application.
Micronutrients are often applied in the liquid form in the seed furrow during planting or in solid form by broadcast application. Micronutrients do not vacate the top couple inches of soil, which leaves them susceptible to washing away from the top of hills. Farmers will use soil tests to monitor the micronutrient levels every few years.
Fertilizer comes in a wide variety of forms allowing a farmer to choose whichever the optimal mixture for their needs. Different forms of fertilizer will carry different prices leaving farmers to calculate the ideal level of nutrients for plant growth, but still allowing them to be profitable.
Although expensive, fertilizer is absolutely essential for increasing crop yields across the world. Farmland is often thought as the input that cannot be substituted, but fertilizer is nearly just as important.
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