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Workman, Kirsten Cynthia

Plant and Soil Science

2020

M.S.

Cover crops play an important role in decreasing erosion and nutrient runoff associated with corn silage production in northern New England. Winter rye (Secale cereal L.) is the primary cover crop species used in this region. While winter rye (rye) monocultures are easily established, they can be challenging to manage in the spring, expensive to establish at recommended seeding rates, and can interfere with the planting of subsequent corn crops. We hypothesized that adding forage radish (Raphunus sativus L.) to a rye cover crop could augment fall performance and enhance the ecosystem services provided by the cover crop and allow for a lower rye seeding rate. A field study was conducted at five locations over a two-year period (five site-years, SY) on commercial dairy farms in Addison County, VT. Treatments included three rye seeding rates, two of which were repeated with and without radish. These were planted with a grain drill and broadcast seeder, for a total of ten cover crop treatments and a fallow (no cover crop) control. Overall, planting method had the greatest impact on cover crop performance. Drilled treatments had significantly greater soil cover in the fall compared to broadcast treatments, ranging from 53.3% to 98.8% cover. The broadcast treatments did not provide better fall soil cover than even the fallow control, except in one SY, and ranged from 25.8% to 68.8% cover. Spring soil cover varied by site year, with little difference between treatments. Similar results were observed in aboveground biomass. Drilled treatments outperformed broadcast in the fall, with drilled treatments measuring 57-776 kg ha-1 and broadcast 22-404 kg ha-1. There was very little difference between treatments in spring biomass, with overall results between 614 and 2496 kg ha-1. The addition of forage radish (3.5 kg ha-1 seeding rate) to the lowest drilled rye seeding rate (67 kg ha-1) showed some evidence of increased fall aboveground biomass and decreased spring biomass compared to rye monoculture, a combination desirable for farmers. Nitrogen and phosphorus concentration in cover crop leaf tissue saw some differences in individual site years, but was not strongly associated with treatment. Total N and P uptake by the cover crop was strongly correlated with biomass production. Soil temperature and soil NO3- were impacted by the presence of cover crop, but there were not significant differences between cover crop treatments. Available soil test phosphorus (modified Morgan), soil moisture and soil NH4+ were not impacted by any cover crop treatment compared to the control. While adding forage radish did not significantly impact the performance of rye cover crops, it did show some promise for optimizing biomass distribution (higher in fall, lower in spring) and warrants further study to identify the seeding rates and planting dates that result in this outcome. This study provides compelling evidence to recommend the use of a grain drill for planting winter cover crops in order to maximize performance and minimize seeding rates.