From the Field-Agronomy Notes: Vol. 2, Num. 6
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April 5th, 2017-
It’s the first week of April and that means that some producers in central and lower Coastal Plain are thinking seriously about transplanting. From a weather and seedling vigor standpoint we’re probably ready to go in most cases, though caution is advised as daily lows will range from the upper 30’s to the lower 40’s later this week. The forecast looks much better next week, so it might be best to allow the cool snap and wet weather to pass. Last year we posted a lengthy article just before the field season started that presented historical weather data for some of the tobacco growing regions in North Carolina. I think the article deserves another look this year, just as a friendly reminder of how wild Mother Nature can be from season-to-season. I also think that we should remember Sunday, April 10th, 2016—that was the day that temperatures fell to 28 degrees across the entire state. I certainly don’t think we’re up against anything that dramatic in the foreseeable future, but it’s worth making note of.
As transplanting quickly approaches, we’ve received a few phone calls regarding fertilizer sources, application rates, and application timings. Some of these conversations have been focused to organic tobacco production, so the intentions of this post are to provide a few options for producers in that category.
Specific to organic fertilizer sources, application rates, and application timing, two major projects have been completed at NC State University. The first study was established to evaluate two sources of organic nitrogen (Nature Safe 13-0-0 and Nutrimax 12-1-0, Figure 1) applied at three rates (+15 lbs N/acre, Base, -15 lbs N/acre). The goal of this study was to 1.) determine the usability of the sources evaluated and 2.) determine appropriate application rates of the sources. Treatments were broadcast applied prior to transplanting at targeted rates, incorporated with a field cultivator, and bedded. Tobacco was transplanted on the same day. At the end of the season we observed that Nature Safe out yielded Nutrimax by a little less than 100 lbs cured leaf per acre (Table 1). Interestingly, application rate did not affect yield (Table 1). Organic nitrogen sources are generally considered to be slow release fertilizers and laboratory studies have consistently shown that nitrogen recovery from the sources used in this study are about 55 to 65 percent of the total nitrogen applied. We consider this to be a factor contributing to the lacking response in application rate, as the actual difference in plant available nitrogen was likely 10 to 15 pounds per acre instead of 30 pounds per acre. In addition, leaf quality was not affected by nitrogen source or application rate (Table 1). This point is just as critical because it also indicates that late season nitrogen release is not likely to impact leaf quality with these sources. With that being said, it appears that either of the two sources evaluated are suitable for organic tobacco production as they are much higher in total nitrogen than other organic sources, are low in phosphorus, and appear to available in many areas of the state. In addition, results demonstrate that application rates of organic nitrogen should mirror the rates used in conventional production. I still have concern that over-application of organic nitrogen sources could result in excessive nitrogen uptake by tobacco, which has a high potential for late-season greening, delayed ripening, increased curing difficulties, all of which are likely to result in variegated-green grades at the point of sale. These concerns are even greater in growing seasons with below average rainfall, as nitrogen release is promoted by good, consistent soil moisture. On the flip side, I also have concern with application rates that are below recommendation. Producers should fertilize for maximum yield and quality, and the way to accomplish this is to apply rates of nitrogen recommended by Cooperative Extension. One additional point to consider is the fact that once nitrogen release from organic sources occurs, ammonium and nitrate become the dominant forms of nitrogen found in the soil. Nitrate from organic sources is the same as nitrate from conventional fertilizer sources; therefore, it is highly leachable when rainfall is excessive. If nitrogen losses occur when fertilizer application rates are below recommendation, leaching adjustments could be required.
|Table 1. Tobacco Yield and Quality as Affected by Organic Nitrogen Source and Application Rate*.|
|Nature Safe 13-0-0||2,458 a||83 a|
|Nutrimax 12-1-0||2,361 b||82 a|
|-15 lbs N/acre||2,384 a||82 a|
|Base||2,387 a||83 a|
|+15 lbs N/acre||2,455 a||83 a|
*Treatment means followed by the same letter within the same column and factor (N source or Application Rate) are not significantly different.
**Base N application rates were 70 lbs N/acre and 75 lbs N/acre in Kinston and Oxford, respectively.
In the second study, the same two organic nitrogen sources were evaluated and were applied using three different methods: 100% broadcast pre-transplanting, 50% broadcast pre-transplanting + 50% band applied at transplanting, and 100% band applied at transplanting. Nitrogen application rate was not a variable evaluated in this study, and application rates reflected the base application rates recommended for each location. From this study we saw no differences between the Nature Safe and Nutrimax nitrogen sources, and did not observe differences in tobacco yield or quality among the three application methods evaluated. However, leaf nitrogen content at topping and in cured leaf samples was greatest in the 100% band applied treatments. Nitrogen deficiency was not observed in this study and nitrogen content only differed by 0.20-0.25%, so it is likely that the slight differences were not of agronomic significance. The take away message from this study is that organic nitrogen should be applied before or as close to transplanting as possible to better sync nutrient release with crop demand. The major concern expressed with post-transplanting application goes back to the nitrogen release factors previously discussed—due to the fact that nitrogen must be released, layby and post-layby applications are strongly discouraged. From a practical standpoint, it might be easiest to broadcast all fertilizer prior to bedding. Some organic fertilizers can be difficult to apply in band or sidedress applications because of their physical properties.
Lastly, there are other sources of organic nitrogen that can be considered. The first are pelletized chicken litter products from Perdue (3-2-3 and 7-1-1). Research efforts in tobacco are very limited thanks to a rather severe storm that destroyed a field site last season; however, preliminary data suggest that these materials should perform just as well as the two feather meal sources previously mentioned. Producers should realize that the two Perdue materials referenced here are very much different than raw or composted litter found on-farm. The 3-2-3 and 7-1-1 materials are processed, pelletized, and have a guaranteed analysis so I feel much more comfortable with these materials than with unprocessed litter. If using pelletized litter, consider applying it very similar to Nature Safe and Nutrimax. These materials are also the newcomers to the organic game, and we’ve been told that third party certifiers and companies are allowing use.
The final source that can be considered is sodium nitrate (16-0-0). This material is night and day different from all materials previously mentioned, as it contains a form of nitrogen (nitrate) that is already plant available and does not have to go through mineralization in the soil after application before it is plant available. Historically, the use of 16-0-0 has been capped at 20% of a total nitrogen program. For example, I have taken this to mean that if you are applying 70 lbs N/acre for your entire crop, no more than 14 lbs can come from 16-0-0. There is a lot of debate as to whether or not that cap still exists, so please check with your buying company and third party certifiers to see what they are requiring.
The final comment worth mentioning is that ANY fertilizer material used in the production of organic tobacco should be approved by your buying company and your third party certifier. Organic fertilizer materials are a dime a dozen on the internet, but many times these products have not been scientifically evaluated nor are they approved for use in organic systems or in tobacco production. It is in your best interest to verify everything you do to protect the integrity of your product and the industry.