Nitrogen: The Key to Reducing Greenhouse Gas Emissions

pathways_precisionWith today’s public policy focused on reducing greenhouse gas emissions, farmers can play a key role in making this happen. In fact, by optimizing the nitrogen fertilizer, a farmer’s contribution can come with the side benefit of increased yield and higher profit.

As with every industry, farming contributes to the production of various greenhouse gases. The Intergovernmental Panel on Climate Change says that agriculture is responsible for a fifth of greenhouse gas emissions, which primarily come from the nitrous oxide produced as soil microbes digest the available nitrogen source. Nitrous oxide is listed among the most potent of greenhouse gases.

Soil will, of course, emit nitrous oxide without any help from farming, but the process is greatly enhanced with the application of nitrogen fertilizer—particularly when there is more nitrogen applied than the plants can absorb.

That is where precision ag can play a role in reducing agriculture’s impact on greenhouse gases by limiting the nitrogen rate. But the big question is, how can that be done while at the same time increasing yield?

Click to enlarge
Click to enlarge

Nitrogen is the limiting nutrient factor of corn yields. Every year, farmers struggle with balancing the need to meet yield targets without over-applying nitrogen fertilizer. Agronomists have spent decades studying the nitrogen response curve to find the optimal balance of nitrogen fertilizer. Because yield increases become negligible beyond a certain nitrogen rate, farmers are advised to apply that rate on the curve to maximize their profits (see the point labeled N0 in the chart). Beyond this point, additional money spent on nitrogen fertilizer will not increase net revenue from additional yield.

So to reach our ultimate goal of reducing nitrogen while increasing yield and profits, we have to shift the nitrogen response curve, which is a job well suited to precision agriculture. The power of more data and better analysis gives farmers a better understanding of the land while enhancing the ability to tackle highly variable situations.

In the short term, field mapping makes precise, variable rate fertilizer application possible. The basic system involves attaching sensors to equipment to measure seeding rates and planter metrics in the spring along with yield and moisture in the fall. Software packages like FieldView provide a simple and intuitive interface for all the data captured in farm operations.

These data are needed to determine the variable rates of nitrogen fertilizer for each individual section of a field. Used in conjunction with autosteering and autoguidance, variable rate application is easy and inexpensive and should reduce the amount of nitrogen fertilizer used in total. Using less nitrogen, of course, saves money.

Having a detailed record of farm activity will be vital to understanding how a particular field reacts to different practices and weather conditions, and having better understanding enables better decisions. While there is no demonstrable link yet between yield improvement and field mapping, the cost savings should be enough to justify the investment.

More importantly, better timing of fertilizer placement is essential to the ultimate goal of reducing nitrogen and raising yields in an industry that tends to overuse nitrogen. Farmers traditionally take advantage of downtime in the fall to place fertilizer. Extreme weather is less likely in the fall than in the spring, and any delay in fertilizer placement would create a crunch when it came time to planting seeds. Unfortunately, the traditional fall placement means extra fertilizer has to be used to account for any runoff that may occur in the months before planting.

The latest, high-tech fertilizers enable much more flexibility. New formulations improve the nitrogen uptake by plants, allowing fertilizers to be placed in the spring and “sidedressed” (meaning it can be applied at key stages of plant growth when it is most needed). When the timing is right, the plant absorbs the nutrients without excessive nitrous oxide leakage into the atmosphere.

Weather is always the biggest obstacle to proper timing. Flash floods can quickly wash away recently placed fertilizer, depriving plants of needed nutrients. For this reason, springtime sidedress placement of fertilizer is most effective in dry, irrigated regions, where such extreme weather is rare.

Another downside is that farmers will need to have enough labor on hand to place fertilizer and seeds in the same time frame. Of course, none of these methods will do any good if a farmer, out of an abundance of caution, decides to overapply fertilizer anyway to ensure the plants are not undernourished.

LONG-TERM SOLUTIONS
These short-term improvements provide a strong foundation for a long-term solution that will more fully deliver on the promise of higher yield, lower cost and an improved environmental profile. The key to unlocking the best performance is going to be the development of a seed that optimizes nitrogen fertilizer usage.

The most promising approach to achieve this is to improve high-population planting by developing dwarf hybrids and narrow-row planting. While this remains a distant goal, it is possible to see a few paths forward.

Corn yields have climbed by 45 percent in the past three decades, but the plant yield per seed has remained flat over the same period. This suggests that population increases are driving yield gains, which makes sense as genetically engineered seeds, crop protection chemicals and fertilizers reduce the stresses plants face, allowing for expanded populations.

Unfortunately, there is a population density at which yields level off because of escalating intra-row competition between plants. Once this point is reached, there are two ways to break through the yield ceiling. The first is the development of dwarf corn hybrids. University of Maryland biologist Burkhard Schulz grew an experimental dwarf mutant corn plant that had all the nutrition of a full-size corn plant in a much more compact form, standing just a few feet high. In the words of Schulz, the kernel yield you get from the plant is more or less unchanged, but the biomass of the entire plant is reduced by more than half.”

Small size is an ideal trait for a high-population environment, since it allows more stalks to be grown in a smaller area without competition. More importantly, the dwarf corn may require fewer inputs for the same yield, as a longer stalk requires more sunlight, nutrients and water. Although these plants are still under development and may never be fully developed, they represent a very promising way to improve the yield-population dilemma.

Planting in narrow rows is another possible avenue for breaking through the yield ceiling. Most research in the past 15 years suggests that narrow rows have negligible yield advantages in high-population environments, but this may be due to the use of seeds that are not optimized for this environment. With different genetic engineering, narrow-row planting could improve nitrogen efficiency and increase yields. More research needs to be conducted to understand the effectiveness of narrow-row planting.

Time will tell which solution will deliver higher yields, greater profits and a more benign environmental profile. But it is clear that precision ag will play a key role in improving nitrogen efficiency. The good news is that improvements are possible now that they make financial sense for growers.

Byrum is Senior R&D and Strategic Marketing Executive in Life Sciences – Global Product Development, Innovation and Delivery at Syngenta. Byrum will present the session, “Solving Big Problems: Innovation Through Open Collaboration” at the PrecisionAg Vision Conference on October 19. For more information visit www.precisionagvision.com

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