By Brad Carlson
Historically, when fertilizer prices were low, and environmental concerns were on the back burner, a high nitrogen fertilizer rate was used as a cheap insurance policy to ensure sufficient N availability during the growing season. Over the last several years, water quality issues have risen to the forefront of farmers’ concerns when making management decisions. What needs to be kept in mind is that rate is only one of the four Rs (Minnesota’s nitrogen best management practices), and fertilizer type, application timing and placement can be just as, if not more, important.
A better understanding of how nitrogen behaves in the environment has led many Minnesota farmers to make significant changes to their application practices. The 4 R approach has caused many to consider all aspects of what, where, when, and how much N to apply. To match this, many fertilizer dealers have greatly increased their capacity for fertilizer application during a wider timing window than was available in the past. Nevertheless, many farmers still feel committed to a specific fertilizer type and time to apply, leaving application rate as the only factor left to flex.
While we are rarely able to know with certainty what the best decision is until hindsight reveals what the growing season was like, we now have the tools available to change our management on the fly in ways we previously could not. Additionally, research has shown that following best practices for N management usually pays for itself, even when there are additional product or application costs to consider.
The number one aspect that needs to be considered is that N loss is driven by water. In light soils, this is usually in the form of leaching. In heavy soils, it is usually caused by denitrification associated with saturation. Therefore, considering the moisture status in the soil profile, coupled with the amount of time before the crop needs the N most (usually starting in early June), one can make a reasonable judgement as to whether application is warranted. Dry years have inherently less risk of loss, while wet ones will reward those who delay application until it is necessary. This is also why best management practices are different in the drier north and west parts of Minnesota than they are in the wetter south and east regions of the state.
Overall, farmers need to consider what their ideal management is, then understand the conditions under which changes are necessary. Some farmers have gone to on-farm storage to allow them to apply at the best time and not be dependent on a custom application (be sure to research the rules if you choose to pursue this). A slightly less involved step is to acquire your own application equipment.
Research has shown that using starter fertilizer is not necessary under a wide range of conditions. However, when used as part of the total package of N applied, it can mitigate risk and ensure a base rate until an additional application can be made. Additionally, the move back to herbicide programs involving a pre-emergent product allows for the application of some liquid N fertilizer at this time, and in some cases enhances the efficacy of the herbicide.
Late and split applications are advantageous during particularly wet years and on lighter soils. Many farmers have acquired self-propelled spray rigs for pesticides and are finding additional use for them with sidedress N applications. Even if you do not have such a unit, you possibly have a neighbor who does and would be willing to make a custom application for you in addition to the readily available commercial options.
In conclusion, if you understand the factors that require changes to management, and know your options, you can reap the yield and cost savings, together with the environmental benefits, of true 4 R management.
Source : umn.edu