Summer Cover Crops for Organic No-till Broccoli

Cover Crop Seeding + Quality of Stand 

Summer cover crops establish well when either a rain event follows seeding or overhead irrigation is available to use. While using a bag seeder was an effective way to distribute seed evening, incorporating the seed with another bed shaping tractor pass did not produce even stands. This was particularly prominent with the larger seed (soybeans). Bed shaping did not bury the large seed enough and as a result, germination suffered. We also experience reduced germination in the pathways and higher density on the bed shoulders due to the incorporation method. 

Reflections on the stands of each treatment are as follows:

Treatment 1: Tilled after Sunnhemp (100lbs/acre) - Heavy density on the shoulders but overall good germination. 

Treatment 2: Crimped Sunn Hemp (100lbs/acre) - Same as Treatment #1.

Treatment 3: Crimped Sunn Hemp (100lbs/acre) & Millet (50lbs/acre) - Millet thrived in the second year due to more rainfall. 

Treatment 4: Crimped Sunn Hemp (75lbs/acre), Millet (50lbs/acre) & Buckwheat (50lbs/acre) - Millet seemed to be out competed by buckwheat, most likely from its allelopathic effects. 

Treatment 5: Crimped Sunn Hemp (75lbs/acre), Soybeans (50lbs/acre) & Buckwheat (50lbs/acre) - Soybeans did not germinate well and seemed to be outcompeted by buckwheat as well. 

Each year we used a hose reel to irrigation 2-3 times to establish the cover crop. In Year One, following the initial irrigation we experienced periods of drought during the cover crop’s life and this resulted in much of our Japanese Millet being stressed and either dying early on or going to seed much earlier than expected. In Year Two, we had more consistent rainfall following seeding and that extended the days to maturity of the Japanese Millet. 

In both years of this experiment, we broadcast our cover crop seed with an Earthway Bag Seeder followed with the tractor-mounted bed shaper to incorporate seed. This setup resulted in heavy seed incorporation/germination in the bed shoulders and lighter incorporation in the bed top. For the two replications of this experiment, this inconsistency in the cover crop stand created inconsistency in the effectiveness of the crimped cover crop. We would like to experiment in the future with a no-till drill or using a tine weeder to incorporate seed. 

Crimping Event

In 2020, we did not have enough time to crimp more than once as our transplants were ready to go in the ground. Due to this, we had a lot of cover crop regrowth in our plots, mostly sunn hemp and buckwheat. It seemed that the regrowth was coming from side shoot production for both of them. We had the crimper halfway full of water which was potentially too heavy and resulted in more breakage in the covers than damage. 

In 2021 we had 1.5 inches of rain on July 26 and as a result, we pushed the crimping date back to July 30th. By this time, much of the Buckwheat and Sunn Hemp was leaning or partially lodged due to the rain. We filled our rear-mounted roller-crimper halfway full of water and after one pass in the Sunn Hemp and Buckwheat plot, the Sunn Hemp snapped at the base and the Buckwheat was chopped by the chevrons of the crimper. We emptied the crimper of water for subsequent passes to reduce the weight load on the cover crop. At the time of crimping, the oldest Sunn Hemp (Treatment 1, seeded May 15th) was 7ft tall and 10% flowering, all the Buckwheat was in full flower and 5ft tall with minimal seed development, and the Japanese Millet had 40% of the crop in a general grain-filling phase.

In 2021 we were able to crimp again 5 days later, which helped damage any regrowth that had started and resulted in a better weed suppression mat with less competition for our broccoli planting. 

In our attached PowerPoint there are photos of the cover crops throughout their lifecycle, at the time of crimping and their breakdown.

Transplant Success

In 2020, the farm was dealing with several additional challenges that impacted our research - it was our first season farming 12 acres (double the acreage of the previous season), we had an excessively wet spring followed by a dry summer, we experienced heavy aphid and armyworm pressure in our greenhouses and heavy fire ant pressure/girdling of all our broccoli transplants.

In 2021, we invested in a new potting soil mix which allowed for more robust broccoli transplants and reduced our fire ant transplant loss to around 10%. In the tilled sections, we noticed an unknown deformation in 30% of the young broccoli plants (excessive wrinkling of the foliage) and these plants produced small heads. One explanation for the deformation could be that we experienced higher pest pressure in the tilled plots since they did not have the same level of population of predatory insects that lived in the crimped cover crop beds. In addition to the excessive wrinkling, we had a lot of aphids on the tilled section. This could have been a result of excess nitrogen available to the plant due to tilling in the Sunnhemp seeded at 100lbs/acre.  

Cover Crop Breakdown + Weed Analysis

A primary goal of crimped cover cropping systems is to suppress annual weeds. In the first year of this experiment, one of the ways we assessed the effectiveness of our cover cropping was through weed tracking. We tracked perennial & annual weed presence in randomized 5x5 plots in each of the treatments on a bi-weekly basis. We experienced significant cover crop regrowth & reseeding. The following Weed Count Graphs depict the percentage cover of weeds and cover crop regrowth/reseeding. Negative space in the graphs shows properly mulched and covered bed space and broccoli plant coverage.

We experienced the regrowth of cover crops in most of the plots due to ineffective timing of cover crop crimping since at the time of crimping, the millet and buckwheat had produced viable seed and reseeded itself in the plots, and the Sunn Hemp regrew from new growth points. In Treatment 1 Sunn Hemp alone did not suppress perennial weed growth at first but over time the cover crop regrowth ultimately outcompeted both perennial weeds and broccoli. In Treatment 2 we experienced low suppression of both perennial and annual weed growth. In Treatment 3 we experienced high competition from both buckwheat reseeding and soybean regrowing. In Treatment 4 we believe the millet cover crop was water-stressed prior to crimping so it did not effectively suppress perennial weeds however the presence of annual weeds was not significant. In Treatment 5 we experienced a lot of buckwheat reseeding and Sunn Hemp regrowing.

We think there was excessive elongation in the broccoli stems due to light competition with the regrowing cover crop. We tried to knock back the Sunn Hemp regrowth by running the flail mower over the top of the beds. We tracked labor hours by treatment type and this bar graph shows how many times we had to visit the plot with the tractor.  The no-till plots required fewer trips which equated to less time and fuel needed to produce the crops.  The no-till labor hours would have been even lower but we had to make several trips to mow the regrowth of the cover crop.  

In the second year of the experiment, our crimping was successful and there was insignificant regrowth so we decided that in order to have better success with harvest, we would hand weed the treatments and track our labor hours doing so instead of letting the cover crop and weeds grow. This proved to be very effective at knocking everything back and only had to be done once. The primary perennial weeds we saw in our plot were horse nettle and dock. 

Broccoli Yields

In 2020, broccoli yields were highest in the Sunn Hemp and Millet plot with a total yield of 0.249 lbs per bed foot. Overall, there was significant crop loss in the research plot due to transplant loss and plant loss due to disease most likely caused by the cover crop regrowth. In 2021, broccoli yields were almost three times higher per bed foot with the highest yields coming out of the tilled plots, however, the broccoli coming off this plot was of lower quality. The second highest yields came out of the Sunn Hemp, Millet and Buckwheat plot. This mix also created the densest crimped cover crop, with proper matting in the understory and successful crimping of the Buckwheat crop. 

Cash Crop Health

In the first year of this experiment, cover crop regrowth probably also contributed to poor air circulation and may have increased diseases like Alternaria head rot and Bacterial head rot. The second year of the experiment had much greater success and proper formation of broccoli heads with almost three times the poundage per acre as the previous year. 

In our attached materials, there is a powerpoint presentation that is mostly photo-based and provides visual comparisons across treatments and replication years of the projects.