Peas and Sulphur in 2006

Greg Stewart and Peter Johnson, OMAFRA

Peas
Cover crop growth in the fall of 2005 was above average due to early plantings (i.e. mid – August) and a warm fall. By mid-October biomass in many of these cover crop plots, where manure was applied, reached levels of approximately 5500 kg/ha (dry weight) and with significant nitrogen sequestered in this biomass, often with over 100 kg N/ha. Six of these cover crop trials were planted to corn in 2006. At these sites,
the farm co-operators followed their normal cropping practices with the exception that every cover crop plot was split into two sub-plots. One of these sub-plots received no nitrogen beyond that which was applied in the starter fertilizer, while the other received starter N plus 150 kg N/ha at sidedress time. The focus was to determine the cover crops impact on corn yield and on the amount of nitrogen fertilizer that could be replaced by the use of cover crops.

2006 corn yields on most of the cover crop sites were above average. However, even with the outstanding cover crop growth in 2005, the impact on corn yields was quite minor and the nitrogen contribution was significantly less than anticipated. Table 1 outlines corn yields from the Braemar site near Woodstock. At first glance, one could focus their attention on how high the yields were without any manure or nitrogen i.e. 181 bu/ac after a pea cover crop. However our analysis indicates that there was still a very profitable response to some additional nitrogen fertilizer (about 60 - 70 kg N/ha) on plots where manure was not applied and the N credit to the pea crop amounted to only 13 lbs/acre.

2006 highlighted another challenge with cover crops that we have not experienced to any great extent in the past. It appears, based on much of our corn response data that oat and oilseed radish cover crops produced enough biomass in the fall of 2005 that they may have tied up nitrogen to the point of reducing corn yield on those plots where neither manure nor nitrogen were applied. At the Saintsbury site, this was most pronounced, where under the no manure, low nitrogen scenario the corn yields following oats and oil seed radish were significantly depressed compared to the corn following no cover (see Table 1).

Peas, which had an equally large biomass as the other two crops, but which fixes its own nitrogen and has a more favourable Carbon to Nitrogen ratio in the stover, did not cause a similar yield depression. In fact, peas at the Saintsbury site resulted in yields that were nearly 30 bu/ac higher than the no cover option when manure and fertilizer N were omitted. The credit to the peas was estimated at 23 lb N/ac, still quite a ways of from being able to pay for the pea seed and a trip over the field with a no-till drill in August. Our efforts on evaluating peas will continue for at least another year and we will continue to determine N credits, as well as the rotational boost that a pea crop might provide to corn yields.

Sulphur
Recent studies have shown response to sulphur that was not found in previous studies. Sulphur deposition from acid rain and dry deposition, a result of air pollution, has dropped dramatically as efforts to reduce sulphur emissions have been implemented. For the first time in memory, winter canola fields in Grey County in 2005 did not set seed, diagnosed to be a sulphur deficiency.

Canola is a very heavy user of sulphur, needing approximately 15 pounds/acre/year. Wheat requires 12 pounds/acre/year, corn slightly less than this.

Studies by Dr. Kurt Thelen, Michigan State University, found from 0 to 23 bu/ac yield increase in corn yield in 2005, with an average increase of 11 bu/ac, from sulphur application. In 2006, the Middlesex Soil and Crop Improvement Association evaluated dry fertilizers with and without additional sulphur. Two blends of dry fertilized were sourced, one with an analysis of 22-22-0-0 and one with an analysis of 22-22-0-8.5. Co-operating farmers ran split planter trials for the most part, where approximately 120 lbs of product was applied in a starter band with the planter. This effectively delivered 10 lbs sulphur per acre to one half of the planter. The results are outlined in Table 2 and
show no impact due to sulphur at virtually every site, even with some fairly wide ranging soil sulphur test results. It appears that for corn in 2006, sulphur was not a limiting factor. Some of these trials may be repeated in 2007 where we will focus exclusively on lighter textured soils.