From the Field – Agronomy Notes: Vol. 3, Num. 1

— Written By

April 12, 2019-

With a largely successful greenhouse season well underway, From the Field – Agronomy Notes comes back for 2019 just as we begin to gear up for transplanting in the southern and central Coastal Plain.

On average, we typically begin to transplant flue-cured tobacco in eastern North Carolina somewhere between April 10 and 15 (social media pictures indicate that some started yesterday!)  Transplanting often begins about two weeks later in the Piedmont. The initiation of the transplanting season coincides with what we consider to be our last frost event of the spring. A couple of years back we published a note that addressed the probability of the final frost date. That note serves as a great reminder that no matter how mild recent weather events have been, there’s always a chance for a few chilly mornings in mid-April (and sometimes late-April). Fortunately, we’ve not had a frost event in the Triangle in more than a week and the seven-day temperature outlook is great. Although, there does appear to be varying estimates for rainfall (which seems to be normal anymore…).

Aside from air temperature and the threat of frost, other factors should be considered when making the decision to transplant tobacco. Those factors include things such as seedling health/vigor, soil moisture, plant back time following fumigant application, thrips flight models, re-entry intervals following pesticide applications, labor availability, etc. However, one key factor that is often overlooked is soil temperature. Soil temperature is important because it can greatly impact root and shoot growth as well as nutrient availability in the very early portion of the growing season. As tobacco producers, we can make a safe assumption that a warm soil (≥65°F) is ready for transplanting.

Years ago, greenhouse research conducted in Canada demonstrated that maximized tobacco growth was achieved at 72°F (soil temperature). In addition, when soil temperature declined to 57°F, supplemental phosphorus fertilizer was found to help plant growth tremendously (Parups et al., 1960). Not surprisingly, this information mirrors our own knowledge and recommendations very well. In fact, published information from North Carolina tells us that tobacco growth (both root and shoot) is greatly improved as soil temperature is increased from 60°F to 75°F (Osmond and Raper, 1981). Recent soil temperature information collected from weather stations in tobacco growing areas of the state tell us that we’re not quite into the mid-’60s (Table 1).

Table 1. Daily soil temperature averages at research stations in North Carolina. Data collected on April 10th, 2019.

Location April 6th April 7th April 8th April 9th
———————————–°F———————————–
Whiteville 57.6 58.5 60.1 61.9
Kinston 60.6 62.8 66.4 66.4
Rocky Mount 58.8 61.3 64.4 65.3
Oxford 57.2 58.5 60.8 62.2
Clayton 57.4 58.3 61.3 63.1
Reidsville 55.2 56.8 59.2 60.8

Knowing that we have seedlings ready for transplanting and that we’re quickly approaching go time, what considerations should be made when our soil conditions are less than ideal? To be more specific, what can be done when we have a cool soil or a slightly damp soil (because a damp soil is a cool soil)?

Well, the answer to that question is relatively easy – growers might find value in a transplant water fertilizer that supplies about five pounds of phosphorus per acre. Again, tobacco root growth and nutrient availability are often limited in cool, damp growing conditions, so a very small phosphorus charge will help to get the crop up and running. The help provided by a starter will allow faster, more uniform growth – both of which will help crop management throughout the growing season. We have never documented an increase in crop yield when a transplant water product is used; however, the benefits of a uniform crop can be worth their weight in gold.

When selecting a transplant water fertilizer, start by assessing the phosphorus concentration relative to all other nutrients. In general, the concentration of nitrogen and potassium should be very small relative to phosphorus. Likewise, the inclusion of certain micronutrients or organic constituents is not necessary. It is also a good option to consider products that have been tested by NC State University. We have experience with a wide range of materials and your local Extension Agent can provide some guidance here.

What about organic tobacco farmers? Organic tobacco producers do not have access to the commercial starter fertilizers that conventional producers do, and at present, we’re not entirely sure that an organic transplant water fertilizer will provide the same early-season benefits as a conventional product. For example, organic fertilizer products are often very difficult to dissolve in solution – which could create major issues for pump driven setups on mechanical transplanters. In addition, most organic fertilizer sources contain trace amounts of plant available nutrients. As such, mineralization must occur to produce nutrient forms that can be used by plants. This process is variable and can take a significant amount of time to happen, which completely negates the benefit of transplant water fertilizers to early-season plant vigor. Knowing all of this, commercial organic producers might consider pre-transplanting applications of phosphorus-containing fertilizers. The options are certainly limited to a large degree; however, a broadcast application of Nature Safe 8-5-5 could be used for this purpose. Half of the targeted nitrogen rate could be applied (which would most likely supply 20 to 25 pounds of phosphorus). The remaining nitrogen could be sidedressed after transplanting (no later than 10 to 15 days) using a nitrogen-only material.

With a large focus to yield, quality, and consistency in 2019, every small thing we can do as producers should be considered. We know that these starter applications of phosphorus provide benefit every few years, and this is shaping up to potentially be one of those years.

Be sure to check back with us in the coming weeks as we delve into other practices that promote leaf quality!

Post Contributions: Dr. Matthew Vann, Mr. Matthew Inman, and Dr. David Suchoff – Department of Crop and Soil Sciences

References:

Osmond, D.L. and C.D. Raper. 1981. Growth and Nitrogen Accumulation in Tobacco Plants as Affected by Nitrate Concentration, Root Temperature, and Aerial Temperature. Agronomy Journal 73:491-496.

Parups, E.V., K.F. Nielsen, and S.J. Bourget. 1960. The Growth, Nicotine, and Phosphorus Content of Tobacco Grown at Different Soil Temperature, Moisture, and Phosphorus Levels. Canadian Journal of Plant Science 40:516-523.