Can you plant a cover crop into grass?

[Guinevere_Perry]

No-Till Planting of Velvet Bean

By Guinevere Perry (PhD) and Brooke Lee

Velvet bean (Mucuna pruriens) grows well during Florida’s hot and humid summers. It is a vining cover crop, known for its ability to produce an abundance of biomass that quickly covers the ground and smothers weeds. With that in mind we selected velvet bean as a legume to plant as a fallow crop in our research plots.

We hypothesized that velvet bean could be sown directly into a field of grass and that it would, in time, cover the ground and overtop the grass. Benefits of sowing a cover crop into grass/weeds include:

• No need for tillage and related equipment to prepare the ground for seeding.
• Complements a no- or minimum- till farming approach.
• Provides weed control as the vines make a dense mat that blocks sunlight and growth for weeds/grass.

To establish the planting we began by mowing the plots at a height of 8 to 10 cm. The next day the seeds were jab-planted at a spacing of about 50 (between-row) X 20 (in-row) cm. The Haraka planter we used performed well in our sandy soil, resulting in nearly 100% emergence of velvet bean seedlings. It places seeds into the soil as you roll it through the field. It would take longer, but you could accomplish the same thing with a jab planter that plants one hole at a time. See the pictures below of the Haraka and single-hole jab planters.
Haraka (circular jab) planter

Single-hole jab planters

Planting occurred in April, before the onset of our rainy season, so the plots were watered as needed with overhead sprinklers. No fertilizer was applied.

Pictures below show how velvet bean grew over time, eventually providing complete cover and excellent weed suppression.

APRIL 20TH, 2023: shortly after mowing and planting

MAY 19th, 2023: Velvet bean growing with the grass and nutsedge, starting to gain a height advantage

JUNE 12th, 2023: Velvet bean vines spreading to cover the ground and overtopping the weeds

JUNE 19th, 2023: Velvet bean providing complete ground coverage, with vines climbing irrigation poles

Before receiving summer rainfall, we relied almost completely on overhead irrigation. Velvet bean did not grow as well near edges of the plots that received less water from the sprinklers. This created an opportunity to measure velvet bean growth and weed suppression in both scenarios (optimal and sub-optimal velvet bean growth).

Before the velvet bean flowered, while the vines were still growing rapidly (in July), we cut biomass from a square meter in each of two plots. For each sampling, we separated the grass/weeds from the velvet bean, dried the velvet bean and weedy biomass, and recorded dry weights. Results are shown below on a per hectare basis.

Square meter sampling area

CONCLUSION:

Velvet bean provided adequate cover to suppress weed growth. In addition to weed suppression, an abundance of biomass has implications for soil improvement, if the biomass is left in the field. If the vines contain 2% nitrogen for example, plot 1 biomass (14,700 kg/ha) would contain the equivalent of 294 kg/ha (14,700 X 0.02). However, this only occurred with adequate soil moisture. Results show, therefore, that velvet bean sown into grass, with no tillage prior to planting, can succeed as long as it has enough moisture.

[Martin_Tlustos]

Great report, thank you!
I’d be interested to see whether it can also suppress cynodon dactylon or other invasive creeping grasses successfully…

[David_Uhr]

Excellent article and photos. I wonder how long it takes velvetbean to produce seed? Also, could you accomplish this with less seed given it’s ability to spread?

[Guinevere_Perry]

Hi Martin. I found this website (Link Here) that states “Velvet bean is mainly grown as a cover crop and green manure and is one of the most suitable crops for reclaiming land infested with weeds, especially with Cynodon dactylon L., Cyperus rotundus L. and Imperata cylindrica (L.) Raeuschel”.

This suggest that velvet bean maybe effective at reducing Cynodon dactylon growth.

[Guinevere_Perry]

Hi David. As you know there are different lines/types of velvet beans with differences in pod pubescence (hairs), seed color, and growth habit. The plant maturity time and subsequent harvest period depends on the type of velvet bean and local climate. HERE is a link to a paper mentioning that, with 9 lines being evaluated, it took 103 to 160 days for the first pods to develop. You would want to also allow time for pods to mature and dry sufficiently. It could take 5 to 9 months without frost to mature. To get a more specific date for your crop I would suggest two great resources. The first is an older book I referenced above, Velvet Beans by S.M. Tracy (LINK HERE). The second is a great ECHO resource titled, Velvet Beans (ECHO Blog Link Here). We planted a vining type with grey-colored seeds. The crop in the article was planted the last weeks of April and will not be harvested until October.

To address your second question, for this trial the spreading ability of velvet bean appeared to be linked to irrigation and soil health. If you plant less seeds in a healthy soil environment with plenty of weekly irrigation it is likely you will still get good coverage.

[Martin_Tlustos]

Thanks. I have found that in our area (Central Tanzania) with its erratic rainfall, velvet bean often does not perform well enough to compete with grasses. It never really kicks off. In good years with decent rainfall (over 500mm), it grows well, but in not so good years (only about 300mm rain with long pauses in between), it doesn’t.

We do have quite some patches with Cynodon dactylon on our farm, but I didn’t try eliminate it so far, as we had planted fruit tree orchards there, and I didn’t want them to be killed by the velevet beans. We will probably do trials this year, as our trees have grown a bit by now.

My impression is that C.d. stunts the growth of the trees (and we can’t really use it as fodder for our sheep), so I want to get rid of it as much as I can and replace it with friendlier grasses.

[Guinevere_Perry]

@Martin_Tlustos

My impression is that C.d. stunts the growth of the trees (and we can’t really use it as fodder for our sheep), so I want to get rid of it as much as I can and replace it with friendlier grasses.

Hi Martin,

I agree in an area with low rainfall the velvet bean would likely not be as effective at out competing grass without proper irrigation. We irrigated 3 times a week for 3 hrs. a day for the first 3 months during our drier season, but after that it will just receive rainfall. Also, yes I agree the vines could be an issue for young trees as the velvet bean grew on the irrigation risers constantly.

Whatever your final decision, I do hope for your continued success with your farm this year.

[Danielle_Flood]

David Tilton had a question from our Facebook post:

Are the seeds cast on the ground or do they need to be drilled into the soil? How many seeds per square meter do you recommend. At harvest, is the velvet bean crop tilled into the soil as green manure or is it left to decompose naturally?

Thanks for this dynamic conversation!

[Tim_Motis]

Thanks for the question from David Tilton.

Velvet bean seeds are quite large and are best planted into the soil. We planted ours with a Haraka planter, a type of jab planter that places the seeds into the soil as it is rolled along. Our sandy soil is quite soft, so it put the seed down into the soil quite easily–down to a depth of 2 cm or more.

We planted at a spacing 50 (between-row) X 20 (in-row) cm. That comes out to a density of 10 seeds per square meter if I’m not mistaken (.5 m X 0.2 m/seed = 0.1 m2/seed). With this spacing the leaf canopy of the velvet bean plants covered the soil quite quickly.

In the tropics, cover crop residues are often left on the soil surface to protect the ground from the effects of intense heat. In temperate areas the vines are often incorporated into the soil. Stacy Swartz covered the two approaches in a lot of depth in a conversation about no-till farming. Click here for a link to what she wrote.

Thanks again and we’re always eager to hear of your experience.

[AFHGlen]

We have great success using much less seed…spacing 75 cm within the row and 1 meter between rows. However, our goal was weed suppression and not fixing nitrogen. Therefore we allowed plants to grow full season producing seed. That gave it more time to “conquer” the tall weeds and grass. It was during a time of sufficient moisture.