Spring 2008

Using Nitrogen Fertilizers Efficiently not only Increases Net-Farm Incomes, but Is Environmentally Beneficial

The use of N-based fertilizers is a common practice in much of agricultural production because N is usually less available from soils than needed to achieve optimum or desired crop yields. Use of N fertilizers allows growers to increase both the yield and quality of crops that rely on N originating from soil and fertilizer sources. Such crops include small grain cereals, corn, and oilseed crops such as canola and flax. Legume crops including forage legumes such as alfalfa, and pulse crops such as field peas or soybeans do not rely as much on soil and fertilizer N because the Rhizobia species of bacteria that live in nodules on legume roots are capable of supplying much of these crops N needs by transforming atmospheric N gas (N2) to plant available ammonium (NH4+).

The dramatic increase in energy costs over the past couple of decades has resulted in agricultural producers spending more to purchase fertilizers, as well as spending more on fuel to power equipment used to plant crops and apply fertilizer. These increased costs have encouraged agricultural producers to try and use their purchased fertilizer products as effectively as possible while achieving the yields of crops wanted.

The fertilizer industry encourages the efficient use of all fertilizers including N fertilizers by following the so-called “Four Rs of Fertilizer Use”. This includes the following:

1. Apply the Right Rate of fertilizer to adequately meet crop needs while avoiding over application.
2. Apply fertilizer at the Right Time so crop uptake is maximized.
3. Apply fertilizer using the Right Placement method to allow effective crop root interception and uptake, and
4. Apply the Right Form of fertilizer so it is available to the crop.

By following these principles the use of fertilizer by crops is maximized and unwanted losses to the environment are minimized.

N losses to the environment can happen in three different ways, one is when nitrate (NO3) is leached down through the soil below the rooting depth of crops and can contribute to excessive NO3 concentration in ground and surface waters. Another is ammonia (NH 3) volatilization losses to the air from soil and plant residue surfaces when the urea molecules in urea containing N fertilizers are hydrolyzed to release NH3 and carbon dioxide (CO2). The third way is when nitrous oxide (N2O) is released to the atmosphere resulting from the reduction of NO3 and to a lesser extent nitrite (NO2) in soils under wet or near saturated conditions. Emissions as N2O are of specific concern because it is considered one of the greenhouse gases (GHG) contributing to global warming. The other GHG compounds involved are CO2 and methane (CH4).

The following are some examples of management practices used in the Northern Great Plains that can help increase crop utilization and minimize unwanted N fertilizer losses.

• Apply N fertilizer close to the time of planting in the spring if possible. If fall application is used the application is delayed until later in the fall when soil temperatures are below 50 °F (10°C). (Right Timing)
• Band place N fertilizer below the soil surface. This can be done in the fall or early spring prior to planting or in a precision band away from the seed row during the planting operation. (Right Placement)
• Take soil samples from fields prior to fertilizer applications and have the samples analyzed for plant available nutrients. The soil test results along with estimates of soil N-mineralization, crop needs, and likely moisture conditions can help determine the rate of N fertilizer required to achieve target crop yields. (Right Rate)
• Apply surface applications of urea containing fertilizers early in the spring as opposed to late spring or early summer. The normally cooler early spring air temperatures result in less potential for ammonia volatilization losses, and a greater chance of early spring moisture moving the dissolved urea into the soil away from the soil surface. (Right Timing)
• If surface applications of urea are done when air temperatures are warmer in the spring or early summer and moisture from rain or irrigation is not consider treating the urea with an urease inhibitor additive to reduce the potential losses from NH 3 volatilization. (Right Form)

Reduced losses of N fertilizer also means increased net farm incomes as crop yields are increased because of reduced losses from the amount of N applied. Economic and environmental benefits are both realized when N fertilizers are used efficiently.