From the Field – Agronomy Notes: Vol. 4, Num. 1
February 13, 2020
Greetings, and welcome to the first 2020 edition of From the Field – Agronomy Notes! This newsletter is being released at the onset of a new growing season that is filled with a lot of hope, well wishes, and uncertainty.
As we kickoff the 2020 growing season, the Tobacco Extension teams have been very busy with county meetings, research conferences, and the Tobacco Short Course. We managed to host 15 meetings this winter and estimate that we interacted with about 1,400 tobacco farmers across the state. We also participated in the 49th Tobacco Workers Conference in Louisville, Kentucky (Figure 1) and conducted the 2020 Tobacco Short Course here in Raleigh. Now, as the meeting season ends for us, we transition to real-world conversations and decisions focused on the upcoming season.
As always, I find that general reminders about fundamental greenhouse practices are useful conversations this time of year. What follows are a few of those practices that we think need specific focus over the next few weeks.
If you were to ask what the average greenhouse seeding date in North Carolina was, I’d tell you Valentine’s Day! With the holiday just around the corner (tomorrow…), one might take a hard look at the weather forecast and scratch their head a bit. Air temperature is well above normal, and I’ll argue that our winter season has largely been non-existent except for a few cold snaps here and there. Even more interesting is that the USGS has shared weather updates indicating that Spring has literally sprung across the southeast (earlier this year than any time on record)! With that being said, air temperature probably is not going to play a major factor in our seeding decisions this season as it is not extremely cold right now and we can always manipulate greenhouse temperatures. On the flip side, I’m very concerned about light quality and duration because of the cloudy conditions that seem to be hanging around. Our standard recommendation is to seed when there are five consecutive days of clear skies in the short-term forecast. As I look at the local news here in Raleigh, I’m afraid that those consecutive days aren’t readily apparent – and I’m not sure they’ll be found anywhere in the state. This means that if we cannot wait to seed tobacco, then we may have to accept slight delays in seed germination or even slight variability in germination rates. The delay in germination is not terribly concerning, as long as the delay is uniform across the greenhouse. In contrast, staggered germination can be quite detrimental to total plant stands. Research conducted in the early 2000’s here in North Carolina tells us that transplant usability declines when seedling emergence is not uniform.
Assuming that light availability is limited due to cloudy conditions, what can we do to minimize any negative impacts from these conditions? Our first recommendation would be to closely monitor greenhouse temperature. We have known for years that seed germination is faster and more uniform when we allow nighttime temperature to dip as low as 68°F and daytime temperatures to climb as high as 86°F. One major reason that this fluctuation promotes germination is because it “tells” the tiny tobacco seed that it’s on top of the soil and that conditions are favorable for growth. In contrast, one of the worst things we can do as greenhouse managers is to maintain a constant temperature. Constant temperatures that do not fluctuate tell the seed that it’s buried in the soil (where temperature fluctuation is less extreme). Tobacco seed to do not have enough energy reserves to push upward through the soil profile like corn or soybeans, so seed germination declines greatly. If we flash forward by about two weeks after seeding (when maximum germination should be achieved) we can reduce our temperature minimum even further (to 55°F) without hurting anything (and saving money!).
The second major thing we can do to promote stand uniformity is closely monitor float water chemistry. To do this we first need to know what our source water chemistry is because this will help us correctly identify any areas of concern. The common areas of concern are things such as high bicarbonates, low boron, high chloride, or low pH. A source water sample collected prior to seeding and analyzed by a public or private testing laboratory will help make these determinations. Nearly all of these issues can be addressed before we even float the first tray. The next thing we can do is wait about 7 to 10 days before adding our first application of fertilizer to the float water. If you observe a delay in seed germination from the cloudy conditions, then you might consider delaying the application by another day or two in order to reduce the potential for soluble salts injury. Growers are strongly discouraged from delaying fertilizer applications by much more than 12-15 days after seeding to prevent uneven growth resulting from low nutrient availability. The second fertilizer application should be made about three to four weeks after seeding. In addition, the total nitrogen concentration should not exceed 150 ppm in a single application.
As a whole, if we work to control everything that we can, we can minimize the negative effects of the factors out of our control. If you have questions about this information or other topics, feel free to reach out to your local Extension agent!
Post Authored by:
Dr. Matthew Vann – Tobacco Agronomist, Dept. of Crop & Soil Sciences
Daniel Ostrowski – Field Crop Agent, N.C. Cooperative Extension of Caswell County