A tool in crop production that is gaining in popularity among Saskatchewan producers in recent years is the split application of nitrogen fertilizer. Many producers view the technique as a risk management tool for dry land cropping. The gain in popularity has been brought on by the advent of new technology, increased research into post emergent fertility, and most of all the poorer soil moisture reserves and the drier seedbed conditions that we have been faced with during spring seeding, especially in the last few years.
In most cases nitrogen fertilizer is the most costly nutrient in any fertilizer program. Placing all the nitrogen requirements into drier soils at seeding time is like putting all your eggs into one basket. By doing so, producers must rely on adequate rainfall to provide the crop growth necessary to utilize the nitrogen placed at seeding. Split application is the process of matching nitrogen supply with crop demand, and then supplying the remaining nitrogen as moisture conditions improve and yield potential increases.
Split application of nitrogen in dry years gives producers greater flexibility in their fertilizer program. This practice minimizes the risk of placing all the nitrogen into the ground at the time of seeding. By providing nitrogen to the growing crop when it can utilize it, producers facilitate increased efficiency of nitrogen use. Split application reduces the exposure of nitrogen in the soil to elements that can create losses such as leaching and denitrification. It also reduces the amount of product a producer must handle during the busy seeding period. Finally, proper timing and placement of nitrogen will help manage and reduce nitrous oxide emissions. Nitrous oxide is, of course, one of the greenhouse gases that contribute to global warming.
The following graphs show the biomass accumulation and nutrient uptake for both canola and wheat. Both graphs are consistent in showing a slower response rate of biomass accumulation and nitrogen uptake in the initial three week period following emergence. As we enter the three to five week period after emergence, the plant enters the vegetative phase of its lifecycle where the rate of biomass accumulation and nitrogen uptake is vastly increased. Following the five week period after emergence, we see a reduction in both biomass accumulation and nitrogen uptake as the plant begins the next phase in its lifecycle.
The graphs indicate 75 to 80 percent of the crops' nitrogen requirements are taken up within five weeks after seeding. This nitrogen plays a key role in determining crop yield and, as such, nitrogen split applications require timely management decisions. If the scenario of dry seedbed conditions and poor soil moisture reserves exist and a producer decides to split apply nitrogen, then enough nitrogen must be placed at seeding to facilitate plant development without hampering growth. If moisture conditions improve shortly after seeding, the second nitrogen application must be made some time within the three to four week period after post emergence. The amount of nitrogen applied and the timing of the second application will depend on the amount of nitrogen fertilizer placed at spring seeding and the yield goals set by the producer. In essence, placing the second application at an earlier stage, rather than a later stage, will have a greater impact on yield. The degree of impact will depend on the amount of nitrogen placed at seeding. As the staging increases, additional nitrogen will likely contribute to enhanced protein production.
Although split application is a good risk management tool, producers should be aware of potential problems. In most cases, the second nitrogen application is made at the time of post emergent spraying. This creates time constraints for producers, unless adequate help and equipment are available. In many situations, producers undertake post emergent spraying for weeds in the morning or evening when the wind is down, and place the second nitrogen application during the day when the wind tends to be stronger.
Second, since June is the wettest month of the year, a period of downtime may result. Producers could miss the window of opportunity to apply that second nitrogen application. To avoid problems with delayed application, producers must ensure that adequate starter nitrogen is applied at seeding. This avoids nitrogen limitations between seeding and the second nitrogen application.
A producer who undertakes post emergent fertilizer application may access the necessary equipment from a local Ag retailer, or choose to retrofit existing equipment. There are many methods that can be used to apply post emergent nitrogen, including surface banding, broadcasting, coulter injection, and spoke wheel injection.
Surface banding involves the placement of a concentrated band or stream of liquid fertilizer on the soil surface. High clearance sprayers, pull type sprayers, floaters, or specially designed pull type applicators can be utilized to dribble 28-0-0 (urea ammonium nitrate) onto the soil surface. When retrofitting a sprayer to apply liquid, producers require dribble band nozzles. The nozzles have one to three orifices to create the desired stream. European nozzles have also entered the market, and include up to eight orifices. The cost to modify a sprayer ranges from as little as a few dollars to as much as $30 per nozzle.
Surface broadcasting of nitrogen fertilizer applied post emergent can be accomplished with both liquid and dry fertilizer. Urea ammonium nitrate (28-0-0) needs to be sprayed at low rates on the plant surface, as crop injury will result with increasing rates. Ammonium nitrate (34-0-0) or urea (46-0-0) can be broadcast on the soil surface. Although ammonium nitrate is preferred over urea due to its lower volatility, many Ag retailers do not handle it or are unable to acquire it.
Surface banding provides many agronomic advantages over broadcast application. First, the concentrated liquid fertilizer band decreases contact between the fertilizer and surface residues, therefore reducing the amount of nutrient tie-up in surface trash. As a result, there are more nutrients available to the crop. Second, the application in a concentrated band reduces the risk of nitrogen loss through volatilization. Finally, surface banding reduces the risk of crop injury as the liquid is being dribbled onto the soil surface instead of being applied onto the crop foliage.
Disc or coulter machine applications place nitrogen fertilizer into the soil once the crop has emerged, and provide minimal disturbance to the soil and emerging crop. Nitrogen placement in the soil with this method improves root access to the nitrogen. It also improves the efficiency of nitrogen use, as volatilization losses and nutrient tie-ups with surface residue are reduced.
A spoke injector places fertilizer into regularly spaced pockets or nests below the surface. Fertilizer nesting results in very low disturbance, and provides similar agronomic advantages to coulter banding.
Split application of nitrogen is a tool that producers can incorporate into their farming operation, especially in years of poorer soil moisture reserves. The key to the success of this system would be to apply enough nitrogen at the time of seeding to carry the crop with out hampering yield, until the second nitrogen application can be made.