Nitrogen Applications

By: Ryan Newton, SBC Research Agronomist & Newton Farms

As a grower, I periodically need to take a step back and remind myself to think about what I am trying to achieve and what is being accomplished by my fertility applications, especially nitrogen. There is a mindset surrounding nitrogen fertilization that has been passed down through generations of farmers that believes since some nitrogen is good, more must be better. If your crop doesn’t seem to be growing well, it just needs a little more nitrogen. It has often been my experience when talking with other growers and going over their tissue test results to see their nitrogen levels way over the optimum range, yet they are still slugging on the nitrogen.  It makes us as growers feel like we are in control because we feel that nitrogen makes plants grow, so we give our crop all the nitrogen it needs, plus some.  I still have to fight the impulse to add more nitrogen when things aren’t going quite right, even though my experience tells me that doesn’t work and even leads to more issues.

This last year, we had a field of tomatoes where we were given a variety that I hadn’t grown before. The variety was a smaller vine variety and I was given the advice from the field rep for the canary that I needed to push it to get it to yield, which in his mind meant more nitrogen. I went ahead and followed his advice, and on a year where our other fields were setting personal records, that field performed badly. While we did get a bigger vine, the root system suffered greatly, which really showed up at the end of the season. As we started tapering off water preparing for harvest, the vines crashed. They did not have the robust root systems needed to mine for water when drought conditions hit. All that extra nitrogen I had applied had hormonally directed the plant’s energy into building the part of the plant that I could see yet neglected the root system. That field also succumbed to heavy nematode pressure, an issue we hadn’t seen in years, undoubtedly due to the weak root system. After the season, the field rep told me that that specific variety also had issues all year with heavy powdery mildew pressure and that they were discontinuing using it in their program because of its susceptibility. It seems to me that the issue isn’t the variety, but the nitrogen management approach applied to the variety.

This experience along with others similar are what I remind myself of when my tissue tests show abundant levels of nitrogen, yet I’m tempted to add more nitrogen just for good measure. The reality is, excessive nitrogen leads to weak plants and increased disease and insect susceptibility, plain and simple. So, I try to keep my nitrogen applications smaller and more frequent, and I do my best to match nitrogen applications with my understanding of each crop’s nitrogen uptake demand curve. We also stabilize every pound of nitrogen applied with organic acids in the tank before application. On our farm, this approach has led to a steady decline in pounds applied, while yields have continued to increase.