[SARE: ADVANCING NUTRIENT MANAGEMENT]
Sometimes farmers’ dollars literally evaporate into thin air. Take fertilizer for example:If not applied properly, up to 40 percent of urea fertilizer can escape into the atmosphereas ammonia gas, through a process called volatilization. In “a landmark study,” Montana StateUniversity (MSU) researchers recently found that some fairly simple changes in fertilizer applicationmethods can significantly reduce nitrogen volatilization. Now, no-till wheat farmersin the state are better able to minimize this economic loss and source of air pollution.
A key recommendation developed bythe researchers, whose on-farm study wasfunded by SARE, is that farmers shouldapply fertilizer in the spring rather thanthe winter or fall, and should take weatherconditions into account. They found thatnitrogen losses in the spring averaged 1.9percent, while winter and fall losses were ashigh as 16.3 and 11.4 percent, respectively.Less volatilization occurs when fertilizeris applied on dry ground or in advance ofrain than when applied on wet, snowy or icyground. “A lot is dictated by the conditionsthat follow the application of the fertilizermaterial, as well as the moisture conditionsat the time of the application,” says MSUSoil Scientist Rick Engel.
“This was a landmarkstudy because…weknew we were losingnitrogen, we justdidn’t know how wewere losing it,” saysCurtis Hershberger,a Montana wheatfarmer who participatedin the study.“Nitrogen is a very big inputcost for us, so by mitigating thelosses of nitrogen and improving our crops,it helps our bottom line. It makes our businessso much more sustainable, so we’renot wasting money and having lower yieldsas a result of what we do.”
The study focused on urea applicationsbecause it is the nitrogen fertilizer used bythe majority of Montana farmers. Anothercritical finding was that applying urea witha urease inhibitor—which binds to the fertilizerand helps mitigate its loss—reducedvolatilization by 64 percent.
Montana State University scientist Rick Engel and his team used the integrated horizontal flux method to measure ammonia gasloss as they developed practical recommendations for minimizing atmospheric nutrientlosses. Courtesy Rick Engel, Montana State University
Encouraged by the positive results thatcame from the MSU team’s three years offield trials, approximately 50 percent ofMontana wheat growers have made changesto their nitrogen management practices.The team estimates the collective economicimpact for farmers who have adoptedsome or all of these nitrogen managementrecommendations is $5 million annually.“Any nitrogen loss from the soil system willpotentially impact either yield or quality ofcrops,” Engel says.
Hershberger changed his practices byapplying fertilizer below the soil surfacewhen planting, injecting it directly intothe soil so it does not have the chance tovolatilize. “We feel that the change in managementpractices has been very rewardingto us economically,” he says. “We did havea great expense in changing our seedingequipment to band fertilizer below thesurface, but we think we’ve been paid backjust in the last few years.”
Along with conventional fertilizers, theteam evaluated legume cover crops as anitrogen source—particularly, whethervolatilization was a concern whenterminating a cover cropof field peas, either bymowing or herbicideapplication. Theyfound that only anominal amount ofnitrogen loss wasdetected—equivalentto 0.3 and 0.5percent of the nitrogenin the plant biomass—meaning that farmers whouse field peas for nitrogen do notneed to worry about volatilization losses.
For more information, see the project reportsfor grant SW10-050.
