By Anna Cates
The sugarbeet crop looks outstanding in many areas in Minnesota and North Dakota, and pre-pile harvest is scheduled to begin in mid August 2020. An early harvest provides an excellent opportunity to plant a cover crop in sugarbeet fields.
Cover crops can make a big impact in several ways, even if pre-pile harvest acres represent only a small portion of the whole field.
First, headlands usually will have compacted soils in serious need of remediation. Headlands are a great location to incorporate a large-rooted brassica like radishes, rapeseed, or turnips to loosen the soil. (Be careful to select a radish variety like Defender, Image, and Colonel which acts as a trap crop, not a host, for sugarbeet cyst nematode.)
Second, early harvested strips planted to cover crops act as a windbreak over the winter slowing wind speeds and reducing soil erosion. In this case, including cereal rye, or another overwintering species in the cover crop mix will provide coverage until the following spring.
You can broadcast cover crop seed in pre-pile acres using a spinner-spreader or air seeder ahead of the defoliator, and the beet harvest process can effectively incorporate the seed. After pre-pile harvest, you can either broadcast with light incorporation for best germination, or drill the seed. Note that seeding rates are about 50% higher for broadcast, non-incorporated seed than for drilled, or incorporated seed. Make sure you use tagged, cleaned seed. This should help you know what variety of seed you are planting and the germination percent, plus help ensure you have seed virtually free of unwanted weed seed.
Cereal rye is a great choice for cover crop beginners, alone or as part of a mixture. If sugarbeets are lifted before September 1st, you may wish to plant a mixture of a grass, brassica, broadleaf and/or legume to diversify. Diversifying can offer more carbon sources to build soil organic matter, a variety of root architectures to build soil structure, and can increase cover crop success, as different species thrive in different conditions. However, make note of any soil residual herbicides used on the field as some cover crops have occasionally shown sensitivity to the group 15 herbicides (e.g. Dual II Magnum) used in sugarbeet.
Plan for termination
Develop a plan for terminating over-wintered cover crops in 2021. Assess the cover crop and soil early in the season to determine what spring tillage, if any, may be needed to prepare the seed bed.
If your next crop is corn, plan to terminate cereal rye or other grasses at least 10 days before corn planting. A full rate of glyphosate is reliably effective.
In contrast, soybeans can usually tolerate a shorter window between cover crop termination and planting, and producers have been “planting green” into living grass cover crops.
If “planting green”, be ready to terminate shortly after soybean planting, and follow USDA-NRCS Cover Crop Termination Guidelines to ensure compliance with crop insurance standards, which vary by region.
A shorter window between cover crop termination and planting or termination after planting helps maximize cover crop biomass production and therefore residue coverage and weed suppression in your cash crop. However, this practice increases the risk of disease or insect pest issues in the cash crop and the potential for cash crop yield loss if the cover crop is not successfully terminated in a timely manner.
Table 1. Drilled and broadcast (no incorporation) seeding rates for a variety of cover crops.
| || ||lbs/acre*||lbs/acre|| |
|Cereal rye||Grass||55||83||Can plant until Nov 15, strong spring growth,|
tolerant of many common residual herbicides,
provides excellent residue cover
|Triticale||Grass||50||75||Same as above|
|Winter wheat||Grass||50||75||Same as above|
|Oats||Grass||30||45||Won't overwinter; quick growing|
|Winter barley||Grass||50||75||Sometimes overwinters; excellent residue cover|
|White mustard**||Brassica||4||6||Won’t overwinter; increased sensitivity to|
many residual herbicides; taproots break up
compaction. Choose varieties that are not hosts
of sugarbeet cyst nematode.
|Radish**||Brassica||4||6||Same as above|
|Flax**||Broadleaf||30||45||Use small amounts in a mixture with grass species|
|Winter pea**||Legume||30||45||Plant by Sept 15, won’t overwinter, increased|
sensitivity to some residual herbicides,
fixes some N
|Red clover**||Legume||8||12||Plant by Sept 1, increased sensitivity to some|
residual herbicides, will usually overwinter,
fixes some N
*Rates refer to pure live seed (PLS)Source : umn.edu
**Recommended as part of a mix with grass species. Lower rate to 1-2 lbs/ac for brassicas in a mixture. You can vary the rate of legumes depending on goals for cover crop N contribution to the 2021 crop. Calculate rates for cover crop mixes using the NRCS spreadsheet. Find out more about individual cover crop species from the Midwest Cover Crops Council Selector Tool.