Sustainable Agriculture Practice: Quantifying the Effects of Cover Crop Planting Dates and Seeding Rates on Coverage Rates and Biomass Yields in Delaware
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Abstract
Cover crops have been proven to have many potential environmental and financial
benefits if they are managed properly. However, proper management is dependent on the unique
soil and climatic conditions in the immediate area. Management techniques that are effective in
one geographical area may not be sufficient to support cover crops in other nearby conditions.
While several cover crop research projects have been conducted locally, Delaware is still lacking
important knowledge to provide effective recommendations to farmers growing cover crops.
Specifically, the evaluation of planting dates and seeding rates is needed in order to maximize
the environmental and agricultural benefits of the most commonly used varieties of cover crops.
Currently, the Delaware Natural Resources Conservation Service (NRCS) offers financial
subsidies to farmers who grow cover crops according to their regulations through the
Environmental Quality Incentives Program (EQIP). It has been brought to their attention by
farmers that their planting date deadlines may be earlier and seeding rates higher than necessary
to produce sufficient groundcover and biomass. However, without research data in Delaware to
legally justify changes to these requirements, farmers will have to continue following nationally
established methods for planting dates and seeding rates, in order to receive subsidies.
Primary objective of my research focused on investigating cover crop planting dates and
seeding rates for optimum cover crop density. Ground coverage, spring aboveground biomass, nitrogen (N) removal, and total soil N at termination as affected by species, planting date,
seeding rate, planting method, and their interactions within agricultural systems including no-till
corn and soybean fields were evaluated. Cereal rye, barley, wheat, and rye/clover mixes were
planted with three seeding rates, up to three planting dates, and two planting methods per site:
broadcasted vs. drilled or incorporated with a light disk. Trials were administered at four sites
during the 2015-2016 season and three sites during the 2017-2018 season. Results showed no
benefit in seeding rates that exceeded 94, 101, and 101 kg/ha (84, 90 and 90 lbs/ac) for
monocultures of rye, barley, and wheat, respectively and 45 kg/ha of rye and 17 kg/ha of crimson
clover for mixes (40 and 15 lbs/ac). Even lower rates performed similarly for many treatments
and outperformed high rates in some. Rye at any date prior to November 1 and rye/clover mixes
prior to October 1 are recommended over barley and wheat for better groundcover, biomass, and
N removal. Drilled plots produced greater biomass and N removal than broadcasted sites at equal
seeding rates, but generally produced similar groundcover. Broadcasted plots seeded at 30%
higher rates produced similar biomass as incorporated plots for some treatments, but
incorporating seeds is recommended over broadcasting at later dates and for increased
groundcover. The most consistent result of this study is that cover crops planted at early dates,
prior to October 1, performed better than crops planted at standard dates, prior to October 15,
which outperformed the late planted cover crops prior to November 1. For some treatments,
cover crops planted at the standard dates performed comparably to early dates, but the late date
plots consistently had lower groundcover, biomass, and N removal, regardless of crop, rate, or
method.