One of the perennial problems farmers have when using a single shoot seeding system and want to seed place their fertilizer as a single pass operation at the time of seeding, is getting enough fertilizer into the ground without damaging the seedlings. If one is using a sweep with a good spreader boot, this isn't an issue, but if you are using a low disturbance opener like a knife or spreader tip, you are limited on how much nitrogen can be seed placed. The amount of nitrogen that can be seed placed will depend on a few factors like soil texture, available soil moisture and row spacing. However, a slow release fertilizer can provide an option for farmers who have narrow single shoot openers.
There are two types of slow release fertilizer, one that is becoming commercially available on a limited basis and the other is still in the testing stage. The commercially available one is called Agrotain and is a urease inhibitor type. This means that the urease inhibitor is sprayed onto the fertilizer at the blending plant and this chemical on the fertilizer, slows the conversion of urea to its plant available form. By slowing the release of urea, there is less likelihood of seedling damage by giving time for the plant to establish roots. The second type of slow release fertilizer has a polymer coat. This polymer coat forms a physical barrier that slowly breaks down to release the nitrogen.
Ken Sapsford and I conducted two replicated trials, one at Swift Current and one at Scott. Ken also conducted some demonstration plots using only the Agrotain type of slow release fertilizer at the Kernen Research Farm near Saskatoon and also at Kindersley. We compared four rates at 15, 30, 60 and 120 pounds of actual nitrogen per acre, using a 3/4-inch knife and a 3-inch spreader tip on 9-inch row spacing. Crop establishment at Scott was rather low due to some factors like seeding depth, but establishments at Swift Current were at desirable levels. We were aiming for an establishment rate of 80 plants/square metre. In all cases, the crop establishment was less with the knife as compared to the 3-inch spreader tip. This is not an unusual phenomenon since there is more in-row competition with the crop in a narrow seed row versus a wider spread.
When comparing urea and the slow release fertilizers used in this study, they all had acceptable crop establishment numbers up to 30 lbs/ac of actual nitrogen (N) in both the knife and spreader tip openers. However, when 60 lbs/ac of actual N was placed with the seed, the urea significantly reduced the crop establishment. The Agrotain and polymer coated nitrogen at this rate did not reduce the crop establishment at all at Scott with either opener. At Swift Current, the crop establishment was the same at 60 lbs/ac of N with Agrotain with either opener, but the establishment was reduced with the polymer-coated nitrogen. At the 120-lbs/ac rate of urea, you essentially had a leisurely walk to each canola plant. However, at Scott, although the Agrotain establishment was significantly reduce, the polymer coated nitrogen still had acceptable establishment numbers when using the 3-inch spreader tip opener. At Swift Current, both the Agrotain and polymer coat had acceptable establishment numbers using the spreader tip. At both sites, the knife had poor establishment.
We certainly enjoyed exceptional precipitation during the 1999 growing season. However, even though there was likely some buffering of the impact of the nitrogen on the seedlings in 1999, I believe that some trends are evident. The results indicate that a producer could likely double the rate of nitrogen that are suggested in the Guidelines for Safe Rates of Fertilizer Applied with the Seed as put out by Saskatchewan Agriculture and Food when using one of the two slow release fertilizer products. The 3-inch spread looks like a very good compromise, especially with the low disturbance spreader tip that was used. However, advantages are also there for very narrow openers like knives or disc openers. Although this study was conducted on canola, benefits for cereal crops would also apply. There is also a possibility of a higher potential for protein, but there needs to be more study in this area. Agrotain is the only slow release fertilizer commercially available at this time and it is quite expensive. However, there is research presently taking place that will result in lowering the cost of this product. Slow release fertilizers are not going to result in producers rejecting double shoot openers, however, there is a place for this type of fertilizer for producers who will never apply more than about 50 lbs/ac of actual N. It allows them to continue using low disturbance openers, which tend to have much lower draft and often lower capital cost as well. It is one more tool producers will be able to use in making direct seeding work in their situation.