Aerial Seeding of Cover Crops
Aerial seeding of cover crops can begin even before the existing crop has been harvested. This is especially important in areas where there is a very small window of opportunity between crop harvest and the end of the growing season. Aerial seeding is more risky than drilling, but waiting to seed a cover crop until after harvest may have less than desirable results such as poor stand establishment due to cold temperatures, moisture stress or inadequate growth before winter.
Soil & Weather Conditions
The ideal soil surface is loose and rough, with cracks and/or with moderate residue cover, and moist to al-low the seed to settle into the surface and make good seed to soil contact. Residue cover retains the surface moisture for seed germination, but excessive residue can prevent the seed from reaching the soil.
Success is much higher in areas with good soil moisture and frequent precipitation in late summer or early fall. Broadcasting seed requires enough moisture in the top ½ – 1 inch of soil to ensure enough moisture for germination and establishment. This moisture needs to be present at the time of seeding or should be expected to occur within 10 days of seeding. If moisture is not present and germination is delayed, there is an increased chance of erratic or thin establishment.
Timing of Aerial Seeding
Seeding into standing soybeans can begin at the 50% yellow leaf stage but need to be done before about 25% leaf drop. Narrow row soybeans, 7″ -1 0″, may need to be delayed to the latter part of this time frame to ensure enough sunlight penetration. The leaf drop after seeding will act as mulch and provide good soil cover and moisture conservation.
Aerial seed into standing com when the com plant is dried approximately to the ear, or when approximately 50% of the sunlight can reach the ground between the rows. Just as with soybeans, narrower row plantings, less than 30″ rows, may need to be dried up higher than the ear to allow adequate sunlight penetration. Sweet com, popcorn, seed com production and hailed damaged corn fields are excellent candidates for aerial seeding due to the normally more open canopy.
Aerial seeding into winter annual small grains or grassland/pastures works well also, as long as it is done early enough to allow frost freeze cycles, rain and snow to settle the seed into the soil.
Potential for Herbicide Carryover Problems
Preferably, herbicides should be chosen a head of time, with the desired cover crop species taken into con-sideration. Many times that is not the case, which can limit the cover crop species choices or not make cov-er crops a viable option. First consult the rotation and replant options from the herbicide label or the UNL 2014 Guide to Weed Management, pages 162-173. http://www.ianrpubs.unl.edu/epublic/pages/index.jsp? what=publicationD&publicationid=941
Also soil bioassay test can also be performed by many soil testing labs.
Many factors interact to determine how long an herbicide remains active in the soil, including factors such as the herbicide, soil type, and climactic conditions.
Most aerial applied seeding rates should be 25% to 50% higher when compared to other more conventional methods such as with a drill or planter. Due to usually less than ideal seed to soil contact and shading fac-tors, a lower percentage of seedling establish, and especially in the case of com a portion of the seed can be trapped in the crop canopy.
Cover Crop Species & Mixtures
Turnip is a traditional choice for aerial seeding. They are generally low cost and easy to establish. Deep tap rooted, it breaks through compaction layers, and scavenges nitrogen from deep in the soil profile, while providing excellent grazing potential. Aerial seeding rates @ 4-6 lbs/acre alone
Radish has a thick, deep taproot can break up compacted soil layers and scavenge nitrate from deeper soil layers. It also a highly digestible forage for fall and winter grazing. Aerial seeding rates @ 8-12 lbs/ acre alone
Winter Cereal Rye is one of the most popular cover crops. While it does not have as deep, fibrous root system that annual ryegrass has, it has had 45″ deep roots in mid spring, and is a good scavenger of nutrients. It can be planted later in the fall than other cover crops and has excellent winterhardiness. Very good for erosion control and winter and spring grazing. Also assists in weed control for the following crop. Aerial seeding rates @ 25-100 lbs/acre alone
Annual Ryegrass is a deep-rooted cover crop that tremendous scavenger of nitrogen. Corn following annual ryegrass often yields more and is more drought tolerant due to depth of roots and holding N in the • soil from previous fertilizer and manure applications. It is an excellent for erosion control and makes an excellent forage crop. Most varieties are not winter hardy, but when it survives may be difficult to kill in the spring. Aerial seeding rates@I0-25 lbs/acre alone
Crimson Clover advantages are rapid growth during cool weather, shade tolerance, c n be a significant nitrogen producer and will likely winterkill in northern areas. It can be flown into com at V 4 to V 6 stages before complete canopy. Can applied in the late summer/early fall but needs 5-6 weeks of good growth before winter. Aerial seeding rates @ 10-20 lbs/acre alone
Medium & Mammoth Red Clover can produce significant amounts of nitrogen and has a good root system that is a soil builder. It is easy to frost seed into wheat and can provide excellent forage after har-vest. Establishes well when flown into corn but needs 6-8 weeks of good growth before going dormant in winter or at com growth stages V4 to V6 stages, before complete canopy. Aerial seeding rates@ 8-15 lbs/ acre alone
Hairy Vetch is an excellent nitrogen producer that tolerates lower fertility. To produce significant nitrogen, it needs 5-6 weeks of good growth before going dormant in winter. It must also be inoculated to be productive. One challenge with using is that it contains significant amounts of hard seed that will most like-ly germinate in future years. It is relatively easy to kill. Aerial seeding rates @ 10-20 lbs/acre alone
Other Species to consider: rape, hybrid brassicas, oats, wheat, Italian ryegrass, triticale, ???
Mixtures are generally recommended over a single species. The composition of the mixture will be dictated by the location, soil type, current crop, planned subsequent crop, nutrient management desires, grazing potential, etc.