Examine the benefits of winter kill Sorghum-Sudan grass (Sudex) as a weed suppressing mulch in tomato production

Final Report for FNC09-760

Project Type: Farmer/Rancher
Funds awarded in 2009: $3,650.00
Projected End Date: 12/31/2010
Region: North Central
State: Minnesota
Project Coordinator:
Katie Cramer
Cramer Organics
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Project Information


Cramer Organics, LLC was started in 2004 to provide top quality organic fruits and vegetables to the local communities in the western suburbs of Minneapolis, MN. We farm about 3 acres (total 10 acre hobby farm) using a permanent bed system, and have been certified organic all 7 years of operation. We started with a local farmers market, but discontinued last year to focus entirely on our CSA operation. In 2010, we expanded our CSA operation to 108 members plus started selling to a newly opened co-op in the community of Long Lake. Cramer Organics is a family operation.

We grow standard varieties of vegetables grown in southern Minnesota for our CSA members. This includes greens, tomatoes, peppers, potatoes, brassicas, onions, and others. Details can be seen on our website: cramerorganics.com. Total sales for 2010 were $58,000.

We have been certified organic since 2004 following all the NOP guidelines. We practice crop rotation, cover cropping, on-farm compost, water conservation (drip tape), and non-chemical weed, pest, and disease management.

GOAL: The primary goal of this study is weed control. A secondary objective is the control of blight.

Based on our crop rotation, we selected the fields to seed the Sudex Sudan grass, which would then be planted with tomatoes the following season. The Sudex Sudan grass was broadcasted (using a broadcasting attachment) on 1/4 acre at the rate of 50 lbs per acre in early summer of 2009. Fifty lbs per acre is the recommended rate for cover crops. Sudex Sudan grass was chosen because of it’s ability to 1) create a large amount of biomass over the summer that would winter kill and provide a thick, dead mulch in the spring to choke weeds, 2) ability to control nematodes and disease and 3) ability to kill weeds with allelopathic compounds.

The crop was mowed when about four feet tall, to allow the roots to penetrate deeper and to increase biomass for the killed mulch and further the allelopathic effects. By late summer a large healthy crop had developed. By December, the Sudex had created a dense, mostly dead, canopy of mulch.

In the spring of 2010, looking at the 1/4 acre plot of Sudex mulch, the covering was not as thick as needed to act as a mulch. Weeds were already starting to come up through the sparse mulch. This is when we learned our first lesson - the Sudex Sudan grass had not been seeded heavy enough, the stand was not as thick as it needed to be.

We still went ahead with the plan and strip tilled 135 foot long beds, 10 feet apart. We used the mantis push tiller to do this, which left an exposed area of about 8 inches. We allowed the soil to warm up for a week and then on May 29 planted the tomato starts with a water wheel transplanter, spaced 2 feet apart. Fish emulsion was added when we planted the starts.

The week following planting the tomatoes in the ground, we received 5 inches of rain. This left the tomato plants in standing water for 4-5 days. We added more mulch (hay bales) around the plants to try and absorb some of the pools of water with the intention of then pulling the hay off to allow the soil to dry quicker. Before we could do that we received more rain, leaving more pools of water around the tomato plants. At this point, some would have considered the whole planting a lost cause. The plants had been severely stunted and some were yellowing. But we still proceeded, hoping for a recovery. We did not install the drip tape, but we still put in 5 foot re-bar stakes every 4 feet and used twine to weave around the plants to keep them upright. When the field had dried out more, we sprayed the plants with fish emulsion.

The control planting of tomatoes were planted on higher ground that has sandy soil as compared to the study plot that was on lower ground and has a clay soil. The control planting was never in standing water and recovered from all the rain.

We continued to have heavy rains all early summer. There was nothing we could do for the study plot at this point.

The tomato plants of the study plot did keep growing, but very slowly. By the time their fruit was ripening, the season had changed and temperatures were too cold to get a harvest.


We experienced two major problems that prevented us from getting accurate results:

1). The stand of Sudex grass was not thick enough. In the spring, grass weeds were already coming up through the dead Sudex mulch. We seeded it at the recommended rate of 50 lbs per acre, but from this experience we learned that if you want the cover crop to act as a mulch, it should be seeded 3 times that of the recommended rate.

2). It was a very wet year at our farm, and the plot we chose for the tomato planting in the Sudex mulch was in an area that retained more water, being lower in the field and having a more clay-like soil. In the past, this area has not had a major problem of holding water. In our 7 years of farming, this was the heaviest rains in a short amount of time we have experienced in the early season. This greatly inhibited plant growth, caused early disease and encouraged weed growth. We lost many crops because of all the rain. What we learned from this is that this study needs to be done in a dry area of the field, a higher area with sandy soil, especially since the mulch prevents the soil from drying out quickly and because of the dry growing conditions tomatoes prefer.

We did not have measurable results. The yield was basically none from the study plot. The weed count was similar if not higher than the control tomato planting in a separate section of the field. The results were not what we expected before the season started, but given how the season was going, they were predictable. The conditions of the study tomato planting that were out of our control, were not conditions that tomato plants can thrive in.

One positive observation that is notable is that the study plot got blight 3-4 weeks later than the control plot. This may have been due to the size of plants at the time blight was setting in, but it also could be the result of the Sudex Sudan mulch which is reported to have controlling effects on blight. This should be tested further since blight is so limiting for tomato production.

For this proposal to have been successful, all other growing conditions needed to be right. But we were working with very difficult growing conditions. Therefore, this project was not successful during this season, but tried again, I think it could be. We did learn from our mistakes and those lessons could be applied to another season, adjusting some of the conditions to guarantee more success in general for the tomato plants, making for an accurate experiment. Those things that we learned are:

1. The rate of cover crop seeding should be significantly higher and up to 3 times the normally recommended rate. We also recommend using a grain drill to guarantee more accuracy, over the broadcasting attachment.
2. Both the 1/4 acre study plot and 1/4 acre control plot need to be in an area that is able to dry out quickly and will not be too damaged by heavy rains. The plot needs to be in a higher area of the field and in sandier soil.
3. The weed pressure needs to be the same in both the study plot and the control plot to receive accurate results.
4. Weed pressure (especially grasses) should be low to moderate.

The disadvantages of implementing a project such as this is that there is so much out of one’s control. Once the experiment was under way, there was nothing we could do to change the circumstances. Since Sudan grass has to be planted in the previous season to create the biomass needed for the mulch, we could not adjust the project by planting more in another field.

On July 10th, we hosted a Sustainable Farming Association tour. There were three groups that came out for a tour of the farm. On these tours, we spoke about the Sudex Sudan grass study plot and the specifics of the experiment. At that point, it was already clear that the results would not be accurate because of other conditions. There were 12 people that attended the tours.


Participation Summary
Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.