Assessing the value of oilseed meals for soil fertility and weed suppression

2008 Annual Report for ONE08-081

Project Type: Partnership
Funds awarded in 2008: $9,213.00
Projected End Date: 12/31/2010
Region: Northeast
State: Vermont
Project Leader:
Dr. Heather Darby
University of Vermont Extension

Assessing the value of oilseed meals for soil fertility and weed suppression


Recent projects in New England have shown that growing oilseed crops for on-farm biofuel production has the potential to increase the economic viability of farms through diversification. Oilseed meals would net the highest return if sold as a source of protein for a livestock ration, but there have been several barriers preventing the establishment of this market. There are small amounts of local oilseed meals that are inconsistent in quality detracting from the value of the meal to the feed industry. Farmers producing oilseeds need to find other markets for their seed meal. There is a potential market for the oilseed meal to be used for fertilizer and weed control. In order to develop a market for the seed meal it will be necessary to determine the value of the meals as a fertilizer source and weed suppressant. This project will conduct a replicated on-farm trial to determine the potential of local canola, mustard, and sunflower meals to provide nitrogen and suppress weeds in a high value sweet corn crop. Outreach will be conducted through on-farm field days, biofuel conference, bulletins, and mass media articles.

Objectives/Performance Targets

The objective of this project is to determine the value of oilseed meals as a fertilizer source and weed suppressant under Vermont conditions.

More specifically, this project will conduct a replicated on-farm trial to determine the potential of local canola, mustard, and sunflower meals to provide nitrogen and suppress weeds in a high value sweet corn crop.


Materials & Methods
The research trial was established in May of 2008 at Borderview Farm in Alburgh, VT. The experimental design was a randomized complete block design with four replicates. Each plot was 5 ft x 25 ft. On May 22, the seedmeal was spread on the plots. Sunflower and canola meals were from crops grown and pressed at Borderview Farm. We were unable to locate any available mustard meal in Vermont at the time of the trial, so mustard meal was sent to us from Washington state. Spreading rates were adjusted in order to provide nitrogen (N) at a rate of 100 lbs per acre. Percent N had been determined through previous nutrient analysis of each type of seedmeal. Rate of meal application and nutrient addition was calculated on a per acre basis. We applied approximately one ton of oilseed meal per plot. An uamended plot served as our control. Meal was broadcasted and then disked in lightly.

On June 9, sweet corn was planted at a rate of 32,000 per acre. Due to a shortage of the type of sweet corn we intended to plant (Luscious), we ended up planting another variety as well (Sugar and Butter). We recorded which plots were planted to each variety. Weed emergence was recorded prior to planting and 2 1/2 weeks after planting by recording number and types of weeds in a 2 ft diameter ring placed in two different areas of each plot. After the second weed count, because of high weed pressure we cultivated and hand weeded all plots, in order to prevent crop failure.

Seedling population was recorded soon after emergence. Pre-sidedress Nitrate Tests (PSNT) were conducted at 2 weeks, 4 weeks and 8 weeks after planting to determine amount of plant available nitrogen in the soil. None of the plots received sidedress N. Corn was harvested on August 21, when maturity was reached. Half of each plot was harvested, and total ears, marketable ears, marketable weight, and population were recorded. Additionally, from each plot, 5 stalks were dried for analysis of stalk nitrates – a post-harvest measure of nitrogen status.

The seedmeal amendments were not effective at suppressing either grass or broadleaf weeds in this experiment. We purposefully chose an extremely weedy location for this experiment, a fact that caught up to us in the end when the weeds were threatening to take over the plot. The large majority of the weeds in the plot were quackgrass. The most prevalent broadleaf weeds were galinsoga, lambsquarter, and pigweed.

Soil nitrate was measured using the PSNT, which measures nitrates available to the plant in the soil. Two weeks after planting, the plots amended with canola meal were significantly higher than the control. Mustard meal was the only treatment significantly higher than the non-amended plots. Canola meal had a higher nitrate level, but this difference was not statistically significant. At the time of sidedressing (which would have been at the 4 week measurement), a nitrate level of 25 ppm or higher would indicate that no addition N needs to be applied. Even though none of the treatments reached this level, the higher values would mean that the grower would need to sidedress with less nitrogen, which would translate into a savings on fertilizer for the grower. Eight weeks after planting, the differences in soil nitrate levels were no longer significantly different.

The addition of seedmeal to the sweet corn plots didn’t significantly improve total ears, marketable ears, or weight of marketable ears. Our yields ranged from 1000 to 1238 lbs/acre of marketable weight. These relatively low yields were most likely due to factors such as uneven germination, weed pressure, and corn smut.

There were no significant differences in percent nitrogen or nitrate levels in the stalks, indicating that there was not a significant difference in nitrogen status between treatments. This is consistent with the yield results.

Impacts and Contributions/Outcomes

On Wednesday July 9, a field day was held at the site of the research trial. Karen Hills, UVM Crops and Soils Technician, described the project and the available results to the 80 attendees. We will be writing an article to publicize the results of this project upon completion of the final report and publicizing results from this study at the biofuel conference to be held in Feb. 2009 in Vermont.

The results of this project indicate that seedmeal has a potential value as a nitrogen source for high value crops. There appears to be a difference in the rate of N release between seedmeal types, during the first month after the amendment is added. The rate of amendment for this study was planned to provide 100 lbs of total N. Since the N in seedmeal is in an organic form, it becomes available over time as a result of microbial activity. This may explain why the differences between treatments were not significant at the eight week sampling. The seedmeal was applied at a rate that was relatively low (2.5 tons/acre or less). Growers of high value crops would be more likely to apply the seedmeal at a higher rate (4-6 tons/acre) as “insurance”.

There were a few factors that may have confounded our results. First of all, the 2008 growing season had an exceptionally high amount of rainfall (amount), which made it a difficult year for most crops. Due to a mistake in planning, we had to use two different varieties of corn. The site of this trial was relatively rich in nutrients, due to previous applications of dairy manure. The excessive levels of P and K as well as the 4.1% organic matter may have made benefits to the crop difficult to detect. And finally, the site was exceptionally weedy throughout, which may have put additional stress on the sweet corn.

In our trial, none of the seedmeals showed any ability to suppress weeds. However, seedmeal does show promise as a nitrogen source for high value crops, but may need to be applied at a higher rate and may be more effective on soils with lower fertility. This information could give farmers a market for seedmeal among vegetable crop producers.

We plan to modify our experiment in 2009 to reflect lessons that were learned in 2008.


Roger Rainville
Cooperating Farmer
Borderview Farm
146 Line Road
Alburgh, VT 05440
Office Phone: 8027963292
Karen Hills
Crops and Soils Technician
278 S. Main St
St. Albans, VT 05478
Office Phone: 8025246501