Variations in Dissolved Soil Nutrients in a Temperate Agroforestry Watershed.

Agroforestry and grass buffer practices are believed to reduce non-point source pollution (NPSP) from corn-soybean watersheds, yet little is known about the processes and mechanisms involved.  The objective of this study was to compare dissolved nutrients concentrations in subsurface soils under crop, grass, and agroforestry areas.  The study was conducted on two corn (Zea mays L.)-soybean (Glycine max (L.) Merr.) rotational watersheds with grass and agroforestry (grass+trees) buffers at the Greenley Research Center, Knox County, MO.  Suction cup lysimeters were installed in crop, grass, and agroforestry areas with four replications at 5, 10, 20, and 40 cm depths to collect water samples.  Soil water samples were collected before and after rain events.  Water samples were analyzed for nitrate, phosphate, and chloride concentrations.  Fallow period soil nutrient concentrations were higher as compared to the cropping period.  Soils under the permanent vegetative buffers maintained lower nutrient concentrations than the soils under crop areas.  This could probably be due to water and nutrient use by the permanent vegetation before crops were established and during the growing season.  Soil nutrient concentration at the 40 cm depth was much higher than the sampling points above this depth.  The claypan is believed to play an important role in determining soil nutrient losses, accumulation within a profile, and subsurface movement.  These trends continued throughout the year.  The results of the study suggest that establishment of grass and agroforestry buffers helps reduce non-point source pollution from row crop agriculture by using additional nutrients that would have otherwise been lost in subsurface flow and runoff and maintaining lower concentrations of dissolved nutrients in soil.