NUTRIENT CONCENTRATIONS IN THE SOIL SOLUTION AND SHALLOW GROUNDWATER OF A LIQUID DAIRY MANURE LAND APPLICATION SITE

Land application of liquid animal manures offers the potential for rec ycling large volumes of slurries by using the nutrients available in t he manure for plant growth in place of conventional inorganic fertiliz ers. A study was initiated to determine environmentally and economical ly sustainable liquid dairy manure application rates on a year-round f orage production system. Treatments based on nitrogen application rate s of 200, 400, 600, and 800 kg N ha(-1)yr(-1) were established. This w ork reports on nutrient concentrations in the soil solution of the vad ose zone and in shallow groundwater after three years of land applicat ion. A 96-instrument network of high tension soil solution samplers wa s installed at 0.5, 1.0, 1.5, and 2.0 m depths and used to collect biw eekly samples from June 1991 through September 1994. A network of 72 s hallow groundwater monitoring wells was installed at 3 and 6 m depths and used to collect biweekly samples from May 1991 through September 1 994. Statistically significant NO3-N treatment effects were observed a t the 0.5, 1.0, 1.5, and 2.0 m depths. NO3-N treatment effect were not observed at the 3.0 or 6.0 m depths or at any depth for NH4-N, TKN, T N, PO4-P, and TP. Mean annual NO3-N soil solution concentrations range d from a low of 1.45 mgL(-1) to a high of 22.70 mgL(-1). Concentration s of NH4-N and TMV were low for all depths while PO4-P and TP concentr ations were nearly always below detection limits. After three years of study, treatment effects were clearly observed in the vadose zone. If not for very low subsoil permeability, it is likely that treatment ef fects would have been observed below 2.0 m.