ISSUE 7   June 26, 2008


Interseeding hairy vetch (Vicia villosa Roth) in corn and sunflowers is an alternative opportunity to gain additional biomass production. The vetch can be ploughed or grazed. When seeded at the four-leaf growth stage of sunflower, hairy vetch produced 1423 lb of dry matter per acre (averaged over five environments with four replicates), without reducing the sunflower yield. Although this article will focus on vetch, there are other legumes like sweetclover, alfalfa, and red clover, which can be interseeded in corn or sunflower.

Interseeding can be looked upon as a double cropping system in northern climates. In this specific case, hairy vetch is utilizing sunlight and moisture, which normally are unused in the later part of the growing season. The secondary crop can be used as green manure plow-down or for additional grazing. The benefits of interseeding vetch are: nitrogen fixation by the legume, increased organic matter (after incorporation of the vetch), and preventing soil and wind erosion.

To use vetch successfully good weed control is essential. If seeded into a weedy field, the vetch will grow but it will not compete well with weeds. If seeded in the early summer and left over winter, the following spring it will quickly grow into a weed-choking mat.

Seeding rates should be 15 to 20 lb pure live seed per acre to establish a thick stand. Vetch seed should be inoculated with type C inoculant (similar to pea inoculant) and incorporated to a depth of 1/2 to 1 inch in the soil. Corn and sunflowers, planted in 22-30 inch rows, will provide enough room for a tractor to pass through the field while the crop is growing, to spread the vetch seed. In experiments conducted on commercial fields, a simple broadcast seeder was mounted on the front of the cultivator tractor to distribute the seed; calibration of the equipment is required. Row cultivator equipment can vary greatly in how aggressively it tills. Some seed can be lost if a cultivator buries the seed too deeply. Vetch seed commonly contains 10 to 20% hard seed, which can remain in the soil and germinate in following years. Unfortunately the unwanted plants can be a problem in other crops. This is especially important for organic and no-till producers.

The timing of vetch seeding will influence how well it produces, but uncontrollable environmental factors can affect results. The four-leaf stage in sunflowers was found to be the optimum time to seed vetch. The timing is influenced by the growth characteristics of the sunflower hybrid. For example, if the sunflower grown is a dwarf hybrid with an open canopy, vetch seeding should be delayed to the six-leaf stage to prevent the vetch from growing too quickly and over-running the sunflowers. Conversely, if the sunflowers are a conventional height, seeding at the four-leaf stage is recommended. Figure 1 illustrates that the percent light reaching the soil surface is reduced as the crop height increases. After full bloom the lower sunflower leaves yellow and fall off the plant. At this point the amount of light reaching the understory crop will increase (about 90 days after seeding the sunflower).

Vetch has proven to be a good grazing crop because it is nutritional, fast growing, and produces a large amount of biomass. If vetch is used for grazing or hay, it must be cut or grazed before it produces seed because the seed is toxic to livestock. Cutting or grazing before plants are in full bloom will prevent seed production.

Hairy vetch produces forage which is high in crude protein (approximately 23%) and high in digestibility (60% TDN). These characteristics make it an excellent forage from a nutritional standpoint. When included in an interseeded mixture with corn or sunflower, hairy vetch produces a highly digestible source of forage for livestock, which will compliment the crop residue from corn or sunflowers well.

Hairy vetch
Hairy vetch growing in between rows of sunflower.

Figure 1
Figure 1. Percent incoming solar radiation
available for an understory crop. Interstate 3311
is a standard height sunflower hybrid and
Sunwheat 101 is a dwarf hybrid.

Hans Kandel
Extension Agronomist



The first seven weeks of the corn growing season, at least for most of the state, have not been kind to the corn crop. The cool weather earlier in the spring slowed emergence, exacerbated the challenge of establishing a uniform stand, and slowed root development. This coupled with the excessive moisture in the eastern part of the state has delayed corn development (at least a full leaf behind normal) and resulted in the plants generally looking weak and yellow. The dry and warm weather over the weekend have improved the appearance of the corn crop marginally and crop growth is starting to accelerate. We are still at least 100 GDD behind normal and much further behind last year most fields were knee high by this time last year and waist-high by July 4th.



A few management practices, such as the application of certain herbicides, are growth stage dependant. Therefore, being able to properly identify the growth stage of your corn crop is important to ensuring that management practices are applied at the appropriate time. The leaf collar method of growth staging corn is the method most often used in recommendations related to the timing of herbicides. When growth staging your crop you should begin by obtaining a representative sample of plants from the field or part of the field of interest. Ten plants should be selected at random. If emergence has been uniform, you can probably get by with fewer plants. Remove any soil attached to the plants so that you are able to observe the roots and crown. The number of leaves defines the vegetative stages of corn (i.e. V1 equals the 1st leaf stage). Counting leaves in corn is straight forward as the process is not usually encumbered with tillers and leaves on tillers as is the case in small grains. However, care must be taken to ensure that the earliest leaves are included when counting leaf numbers. The first leaf is small and often dies and is torn from the plant during early plant development. The first leaf has a blunt tip (see photo). Look for sheath remnants at the crown of the plant if you suspect that the first leaf (or second for that matter) is missing. Count only those leaves that have a collar. Do not exclude leaves that have been damaged by hail or frost. The total number of leaves that a plant will developed is more or less fixed for a given hybrid; additional new leaves will not replace leaves that are stripped from the plant.

Early corn leaves
Early corn leaves

In order to determine the growth stage of older plants that have lost their lower leaves, uproot the plant and split the stem with a knife through the root ball. At the very base of the stem, identify the first visible internode. Internodes are the white area between the more yellow bands of the nodes. The first obviously visible internode should about 2 to 3/4 inch in length. The node directly above this internode will be the fifth node, and the leaf arising from this node will be the 5th leaf. Find that leaf and continuing counting leaves from that point.



There is an excellent relationship between corn growing degree days (GDDs) and leaf appearance in most environments. Corn GDDs are calculated using a base temperature of 50 degrees F (average temperature for the day minus 50) and therefore, differ from small grain growing degrees days which use a base of 32 degrees. GDDs for both corn and small grains for locations near your farm can be obtained using NDAWN ( form.html). Corn requires about 120 GDDs to emerge. Researchers from other states have found that it takes about 80-85 GDDs to produce a new leaf through the 10 leaf stage. Data from the last two years in ND would suggest that new leaves appear after about 70 GDDs (see Figure 1). Based on these data, corn planted on May 1st in Fargo this year should now have about 6 leafs (542 GDD accumulated minus 120 GDD for emergence = 422, 422/70 GDD per leaf = 6 leaves). This number corresponds fairly well with what can be observed in plots near the NDSU campus.

Figure 1

Joel Ransom
NDSU Extension Agronomist - Cereal Crops

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