LOSS OF NUTRIENTS FROM CROPLANDS AS A RESULT OF SOIL EROSION IN GRUNDY CENTER, IOWA

An environmental field study was conducted in Grundy County, Iowa from June to September 2004. The purpose of this study was to find the temporal distribution of chloride, nitrate, and sulfate in the hydrologic environment. The goal of the project was to investigate the rate of soil erosion and the subsequent loss of nutrients from the agricultural fields of the study area. Water samples were collected from 6 different sites along the Munns creek in the study area near Grundy Center, Iowa. The average sampling frequency was 7 days. Each sample was analyzed for chloride, nitrate, and sulfate by ion chromatography. Soil samples were collected from 22 locations in the surrounding agricultural fields. At each location, soil was collected from two different depths (surface, and 6 inch). Subsequently, the samples were analyzed for the Total Phosphorus (TP). Universal Soil Loss Equation (USLE) was used to measure soil erosion from the croplands. It was observed from this study that a significant loss of P is associated with soil erosion by suspended sediments transported in overland flow. Also, it was observed that dissolved oxygen was quite variable, ranging from 13.9 ppm to 5.3 ppm. On the other hand, pH was relatively stable, which ranged from 8.39 to 6.84. In June, average nitrate was found to be much higher (99.6 ppm) than chloride (18.0 ppm) and sulfate (17.4 ppm). Over the period of study, nitrate concentration at most sites gradually went down, whereas sulfate concentration went up. The highest TP was found in some of the upstream areas of the drainage network. In June samples, the surface soils had much higher TP than the deeper samples. This is because P was freshly released from the fertilizers applied to the fields in May. Later, there was significant leaching of P to deeper soils following major rain events in the area. As a result, all samples collected in July, August and September had much higher P in deeper soils. However, the loss of P from the upper soil is also attributed to the rapid soil erosion in the area. The Total Phosphorus loads ranged from 0.44 μg P/g of sediments to 377.56 μg P/g with an average of 50.74 μg P/g. It was concluded from this study that soil erosion can significantly impact the temporal distribution of nutrients in agricultural fields.