Reducing Soil Erosion and Nitrogen Leaching through Sustainable Cropping Systems
Project type: On-Farm Research Grant
Project number: OS06-030
Project dates: 2006–2007
Project reports: https://projects.sare.org/sare_project/os06-030/
Heightened awareness about the environmental impact of inorganic fertilizer and intensive, non-diversified farming practices have gained attention in the mid-Atlantic states since the adoption of the Chesapeake 2000 agreement, a plan that seeks to improve water quality in the Chesapeake Bay region. Winter annual cover crops are highly valued for their ability to make use of soil nutrients, particularly nitrogen, which would normally be lost from the soil by runoff and leaching during the winter. Previous studies have shown that cover crops enhance soil stability and reduce erosion and runoff of sediment containing nutrient and pesticide residues. Additionally, cover crops have the potential to increase farm profitability by improving soil productivity. Increased water- and nutrient-holding capacity, greater organic matter and higher nitrogen levels are some of the beneficial effects to the soil associated with cover crops.
Scientists partnered with farmer Paul Davis and his family, whose farm is located on Virginia’s Coastal Plain, for a study aimed at discovering which winter cover crops and planting dates would maximize winter soil cover, return the most biomass to the soil and bring the greatest level of nitrogen uptake.
Methods and Practices
The experiment followed a split-plot design with different crops and combinations of crops planted and then observed over a three-year period (2005–2007). Changes in soil nitrate levels were also closely monitored.
Cover crops of rye, oats, barley, triticale, crimson clover and vetch were planted on different plots either separately or as a mixture of species on three different dates (October 1, October 20 or November 10). Subplots received the following spring nitrogen application rates: 0, 28, 33 or 56 kilograms of nitrogen per hectare (kg N ha). Cover crops were seeded using a no-till grain drill. Each year of the study, all aboveground biomass was hand-trimmed twice. Crop samples were dried in a forced-air oven and sieved through a 2-millimeter screen in order to determine nitrogen uptake levels. Changes in soil nitrate concentration over the cover crop season were determined by taking soil samples at the planting and termination dates of the cover crops. Samples were taken at depths of up to 90 centimeters.
In terms of biomass, rye and rye-vetch mixtures produced more than the other crops across the three years. For instance, for the early and mid-planted treatments in 2006, rye and rye-vetch both produced over 12 metric tons per hectare, compared to barley, which produced less than 8 metric tons per hectare. In terms of nitrogen uptake, rye and rye-vetch mixtures also performed best. In 2005, none of the cereal crops absorbed more than 100 kg N ha, while even late-planted rye had uptake rates of 115 kg N ha. Both biomass yield and nitrogen uptake rates responded positively to increased spring nitrogen application. In 2006 and 2007, for the subplots exposed to 30 kg N ha, biomass increased at an average of 1.45 metric tons per hectare and nitrogen uptake increased by 26 kilograms per hectare. Biomass and nitrogen uptake rates also responded positively to earlier planting dates.
The results of this and other studies led the Virginia Department of Conservation and Recreation to offer a payment of $5 per acre to farmers who plant rye as a cover crop. Presentation of these results at county and regional meetings have also led to a wider discussion on the best use of cover crops with farmers from across the Virginia Coastal Plain.
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