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Cover Crops Planted Into Sunflower (06/18/20)

Soil erosion is generally more common with row crops than with close-growing small grains.

Soil erosion is generally more common with row crops than with close-growing small grains. Sunflower stubble, if cut in the fall below 12 inches, is not effective for trapping snow due to its limited winter surface cover. Recently, agronomists and producers have increased awareness of protecting soil from wind and water erosion. Cover crops, such as legumes, can boost soil fertility, reduce soil erosion and are becoming increasingly important in farming systems. Some potential benefits of intercropping a legume in sunflower are atmospheric nitrogen fixation, soil erosion control, improved snow trapping, improvement of the soil aggregation and organic matter content, and fodder or green manure production.

In general, the rate of sunflower development is mainly influenced by temperature. Therefore, cumulative growing degree-days are a valuable means to show differences among growing seasons (See current estimated sunflower growth stages). Water is the major limiting production factor for sunflower in the northern Great Plains. Intercropping is not a new concept, as it is a common practice in tropical countries. Clearly, from the producer's perspective, the primary crop component (sunflower) should yield near its potential when planted at its optimum plant density. The legume, or secondary crop, planted at lower than optimum plant density, is expected to yield below a legume or other cover crop planted as a sole crop. The primary crop (sunflower) should be planted first to have competitive advantage. The primary crop will receive full sunlight at the top of the canopy. The secondary crop, farther down the canopy, will have long periods of dim light, with short exposure to near full sunlight caused by holes in the canopy when upper leaves move. Different areas of the cover crop leaves will be exposed to solar radiation, due to the change in sun's angle during the day and over the season. Shading by sunflower influences the photosynthesis and atmospheric nitrogen fixing ability of the intercropped legume. For most cover crops grown in shaded conditions, growth is reduced. Some legume species, however, continue to fix atmospheric N while shaded. Nitrogen applied to legume-based intercrops will usually favor the growth of the non-legume crop and reduce N-fixation by the legume. Results from intercropping experiments are often field specific and seasonal variation is high.

Intercropping naturally causes plant competition between primary and secondary component crops for water, nutrients, light and carbon dioxide. Production of total biomass produced in an intercrop system compared with their sole crops can be increased if more solar radiation is intercepted. This can be achieved by minimizing the proportion of radiant energy that reaches the soil (greater radiation-use efficiency) or by use of solar energy by the component crop when the primary crop is senescing (yellowing of the leaves in the fall). Cultural practices, like time of planting of the respective component crops, planting pattern, fertilizer application and pest control strongly influence the relative competitiveness of the primary and secondary crops.



In my experiment, legumes were interseeded into sunflower on the day of sunflower planting, at the V4, and V10 growth stages of sunflower. Legumes included, and their seeding rate were: hairy vetch (28.8 lb/a), sweetclover (9.5 lb), alfalfa (16 lb), black lentil (22.3 lb) and snail medic (22.3 lb). The sunflower yield was reduced when legumes were interseeded at the same time as sunflower planting, except for black lentil (which produced 1237 lb of legume biomass). The sunflower yield, head diameter, achenes per head, and 100- kernel weight were not significantly lower when legumes were interseeded at the V4 or V10 growth stages. The amount of legume biomass produced is indicated in Figure 1. Legume biomass was lower when the legume was interseeded at the later (V10) growth stage.


Hairy vetch produced the most biomass but the crop is difficult to kill and may become a ‘weed’ during a subsequent season. Better results of cover crop establishment are achieved when the seed is covered with soil. At the drier environments, legume biomass produced was low, indicating the need for sufficient moisture for the intercrop. Although in this experiment only legumes were tried as an intercrop, it is anticipated that other adapted species can also work as a cover crop. More research is needed to identify these opportunities. This research focused on interseeding at the vegetative stage of sunflower. Experiments with corn and soybean have shown that there might be opportunities to aerially seed winter hardy cover crops at the end of the growing season. Near maturity, the sunflower canopy is opening and light will be available for a cover crop to establish. Establishment will depend on available moisture at the time of sowing.


 Hans Kandel

Extension Agronomist Broadleaf Crops

This site is supported in part by the Crop Protection and Pest Management Program [grant no. 2017-70006-27144/accession 1013592] from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed are those of the website author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

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