Early-season nitrogen test


FARMERS HAVE SEVERAL important decisions to make when it comes to applying nitrogen via fertilizer; primarily, they need to decide how much to apply, and when. Typically, nitrogen is added to the soil before planting, with the possibility of a side-dress application mid-season. In order to decide whether or not to side-dress, farmers must determine whether the crop will respond positively (otherwise it will be a waste of time and money).

Plant agriculture professor Manish Raizada runs the Laboratory of Inexpensive Maize Biotechnology at the University of Guelph, which is focused on developing low cost biological technologies that are meant to enable farmers around the world to use less fertilizer and fewer pesticides more effectively.

Raizada’s current project addresses the uncertainty and high cost of applying nitrogen fertilizer after planting, or side-dressing. While it certainly appears that the project has yielded a method of N testing that is significantly less expensive, it will take more testing to determine how effective it is.

All crops absorb nitrogen from the soil, usually in large quantities. Nitrogen exists naturally in soil, but is largely tied up in organic matter, and only a small amount is available to crops at a given time. Microorganisms gradually release usable nitrogen into the soil by breaking down organic matter. Crops and other plant life convert nitrogen into amino acids and eventually proteins, used in cell division. Nitrogen also combines with chlorophyll to turn sunlight into energy. Nitrogen deficiency can drastically affect the health of a plant and a crop’s yield.

The most common nitrogen tests do not perform particularly well early in the season. These imperfect tests mean that growers either don’t have enough nitrogen for their crops or they over-fertilize, both of which will hurt their yield.

The timing of applications can have a significant affect on how well the corn plant utilizes nitrogen. 

Growing plants only have so much capacity to take up the nitrogen made available to it. Raizada hopes that easier and more effective testing will make growers more likely to spread their nitrogen distribution across the season, wasting significantly less of it. “If we can work with growers, for them to add nitrogen as needed when it’s needed, it could save growers thousands of dollars.”

Testing with enough frequency and accuracy to make smart decisions about nitrogen distribution is expensive, time-consuming, and not as accurate as Raizada believes it could be. Direct soil testing only reveals the total soil nitrogen content, not the useful bioavailable portion. Other testing options such as a SPAD metre (soil plant analysis development) or Greenseeker measure nitrogen content in the plant itself, but only indirectly — they measure chlorophyll in the plant’s leaves, which has an indirect relationship with plant nitrogen content. Raizada believes that leaf concentrations of the amino acid glutamine could be a more accurate indicator of plant nitrogen status early in the season, and he has developed an inexpensive test to measure it. He hopes to prove the test’s effectiveness and value through ongoing research, funded in part by Grain Farmers of Ontario. Because soil nitrogen is converted into Glutamine both before and after transport to leaves in cereals, Raizada says “there is an excellent correlation between addition of nitrogen fertilizer and the concentration of free glutamine in leaves.”

The test uses the molecularly engineered biosensor named GlnLux. Testing involves taking leaf punches from young corn seedlings, grinding them up, and adding them to GlnLux bacteria. GlnLux converts free glutamine from the leaf punch samples into light, which is measured by a luminometer.

Raizada’s method has already been tested with punches taken from early corn seedlings from a field in Woodstock, as well as ongoing testing in a controlled greenhouse to streamline the methodology. The goal is a test that can be processed at a cost of $1 per sample and a daily rate in the thousands. The testing itself is simple, taking approximately two minutes to process 96 samples. Because of the low cost, Raizada says, “a grower can sample more, and probably more critically, sample at different times. Depending on what is going on with rainfall and temperature, sampling at different times may be very informative.”

Eventually, Raizada hopes that growers will be able to purchase a kit, send their samples to a lab via courier, and get their results online within a day or two. The GlnLux approach could also eventually be turned into an on-farm test for even quicker results.
University of Guelph PhD student Travis Goron has already begun two years of field testing to determine whether the newly optimized test can help growers make informed decisions about their own soil nitrogen applications. On the site of an existing long term corn trial at the Elora Crop Research Station run by University of Guelph colleague Bill Deen and others (it started in 2008 and is set to run until 2018), Goron will collect data on hybrid corn (Pioneer 38B14, planted in 30 inch rows at 32,000 seeds/acre, conventional tillage) treated with starter nitrogen and side-dressed with different rates of urea and ammonium nitrate. The trial will also systematically compare the GlnLux test to other available technologies to determine which is the most effective; the existing long-term trial is already measuring the relationship between plant nitrogen and grain yield, and conducting soil nitrogen, GreenIndex, Greenseeker, and SPAD tests.

Ultimately, Raizada and Goron still need to prove that the GlnLux method can be used by a grower to decide whether or not to side-dress (and how much), but early returns are positive and Raizada maintains the importance of more accurate nitrogen testing.

“Synthetic nitrogen uses a lot of natural gas because it requires a lot of heat to make ammonia, so fertilizer prices are tied up with natural gas prices. If we can help growers manage nitrogen better, especially in the decades ahead with fuel prices likely to increase long term, we probably need to manage nitrogen better, not only in Ontario but worldwide.” •

About Mark Carter 5 Articles
Web Coordinator, Grain Farmers of Ontario