INFLUENCE OF COVER CROPPING ON NUTRIENT LOADING FROM TILE-DRAINED AGRICULTURAL WATERSHEDS

Nutrient pollution originating from agricultural regions in the Midwest leads to pollution of drinking water sources as well as large hypoxic zones in the Gulf of Mexico. One method shown to reduce this pollution is the planting of cover crops, which have been shown to significantly reduce nitrate and phosphorous exported from agricultural fields, even in tile-drained watersheds that are resistant to other nutrient management methods such as riparian zones. However, most cover crop studies take place in small agricultural study fields, which may display different nutrient loading responses to cover cropping than commercial agricultural fields, which are often much larger. These studies also often use low resolution water sampling (weekly or bi-weekly). In this study, we use high resolution nutrient monitoring methods to determine the effectiveness of cover crops on a watershed scale in reducing nutrient loading. We compare nitrate and phosphorous loading from two agricultural watersheds, one of which is 1000 acres and planted with rye and tillage radish while the other is 700 acres with no cover crops planted. To obtain high-resolution loading data, we use automated discharge measurement and automated water sampling at both watersheds. By comparing loading between the treated and untreated watersheds, we can determine whether cover cropping reduces nutrient loading, with the secondary goal of comparing loading measured with high resolution sampling versus loading measured via bi-weekly sampling. Preliminary results indicate that high resolution sampling allows for more accurate nutrient loading measurements because of its increased ability to measure short peaks in loading caused by storm events. For example, in an early May storm event where 2.63 inches of rain fell in 3 days, total phosphorous loading at our untreated cropped watershed increased from a pre-storm level of .014 kg day^-1 on May 7th^th to 13.61 kg day^-1 on May 10^th. Spikes such as these are mostly missed by bi-weekly sampling. We also are finding evidence that cover crops are reducing and stabilizing nutrient runoff from our treatment watershed, especially during storm events. This may indicate cover crops have the potential to reduce problematic nutrient runoff from Midwestern agricultural areas, even when planted over large agricultural fields.