Soil properties, hydrology, and water quality of perennial vegetation on undisturbed soil in southwestern Minnesota.

摘要

Three experiments were conducted measuring the soil properties, hydrology, and water quality of perennial vegetation on undisturbed soil with no history of row crop production, an adjacent field with a long history of row crop production, and a recently converted row crop field.;The conversion of perennial vegetation on undisturbed soil to agricultural row crop production greatly affected the soil physical and hydrologic properties. Soil bulk density values were lowest from soil with perennial vegetation on undisturbed soil. Following the conversion to agricultural row crop production, there was a statistical significant (p-value= 0.05) increase in soil bulk density at the 0--10 cm, 40--60 cm, 60-80 cm, 80--100 cm, and 100--120 cm soil profile depths. Infiltration rates were reduced between 39 and 80 percent, respectively, and hydraulic conductivity rates were reduced between 41 and 67 percent, respectively, at 4 different soil moisture levels. These changes resulted a net reduction in the amount of water that infiltrated in the soil of a field recently converted from perennial vegetation to agricultural fields. The soil bulk density values, infiltration rates, and hydraulic conductivity rates of the recently converted cropland were similar to an adjacent agricultural field with a long history of crop production.;The second experiment used a paired watershed design with 2 small watersheds (0.31 ha and 0.4 ha, respectively) of perennial vegetation with no history of soil disturbance (tillage) to examine surface water hydrology and water quality characteristics. The control watershed had perennial vegetation on undisturbed soil for the entire experiment. The treatment watershed was converted to corn (Zea mays) production following a 2 year calibration period. Runoff was limited throughout the experiment because of weather variability, soil surface residue, vegetative cover, and well developed soil, and represented 0.26 and 1.16 percent of the precipitation received in the control and treatment watersheds, respectively, throughout the 4 year monitoring period. Runoff from the control watershed was observed only during frozen soil periods during snowmelt in 2 of the 4 years and totaled 2.21 mm in 2012 and 3.71 mm in 2014.;Runoff from the control watershed did have elevated concentrations of nitrogen and phosphorus, however, overall export from the watershed was small given the low runoff volumes. Total suspended solids (TSS) and yield and flow weighted mean concentration (FWMC) from the control watershed during snowmelt periods were low. Snowmelt runoff characteristics of the treatment watershed were consistent with the control watershed during the calibration period. During the treatment period on frozen soil, the treatment watershed had 81 percent less runoff, 58 percent less total nitrogen (TN) yield, and 77 percent less total phosphorus (TP) yield than the control watershed. These reductions were unable to be tested for significance as a result of insufficient runoff events. It was hypothesized that the corn (Zea mays) residue in the treatment watershed was less effective than the perennial vegetation in the control watershed in capturing snow prior to the snowmelt periods. However, TSS FWMC increased with runoff on frozen soil in the treatment watershed likely due to the soil disturbance (tillage) that was required during the conversion to corn (Zea mays) production in 2013.;In the first year of corn (Zea mays) production in the treatment watershed, 4 runoff events on non-frozen soil in June resulted in 18.5 mm of runoff, and yields of 2.02 kg ha-1 TN, 0.27 kg ha-1 TP, and 1,060 kg ha-1 TSS. These precipitation events did not produce runoff from the control watershed, and the increased runoff and yields are associated directly with the conversion of perennial vegetation to corn (Zea mays) production. There was no runoff in the treatment watershed over non-frozen soil in the second year of corn (Zea mays) production using no till methods.;The third experiment used nested watersheds to evaluate the differences in surface runoff, and nutrient and sediment export. This experiment evaluated the differences in hydrology and water quality of an agricultural watershed nested in a watershed dominated by perennial vegetation. The "above" watershed (0.27 ha) was used for row crop agricultural production and was nested in the "below" watershed (0.96 ha) that had 72 percent of the watershed composed of perennial vegetation on undisturbed soil. Annual precipitation values were 24 percent below normal in 2013 and 8 percent below normal in 2014, however, there were 7 individual days with at least 25 mm of precipitation including 3 days with at least 50 mm of precipitation.;The above and below watersheds exhibited different runoff characteristics, including differences in the partitioning of runoff observed on frozen and non-frozen soil. (Abstract shortened by UMI.).