Phosphorus distribution and availability in response to dairy manure applications

As livestock operations become larger and concerns about water quality beco me greater, attention must be paid to the composition of animal manure and its potential impact on the environment. One current concern involves the a mount and forms of phosphorus (P) being added to land with manure. The obje ctive of this experiment was to determine the forms and availability of P i n soils receiving 4 years of continuous dairy manure applications. Soil sam ples were collected from lysimeter plots established in 1991 to study the i mpact of dairy manure applications on surface water and groundwater. Soil P was fractionated into available (NaHCO3), iron (Fe)- and aluminum (Al)-bou nd (NaOH), and calcium (Ca)-bound (HCl) forms. These data were related to m anure application rates, soluble P concentrations, and anion exchange membr ane (AEM) bound P. Results indicate that the potential to move P by leachin g through these loessial soils is very low even at high manure application rates. Large manure additions resulted in increases in all P forms; however , the inorganic pools increased more than the organic pools. The AEM values were a good tool for predicting potential P movement by soil erosion or ru noff with membrane bound P being strongly correlated with manure applicatio n rate (r(2)=0.82) and available P (NaHCO3). Best management practices for manure disposal need to consider the potential for P movement through erosi on and runoff, and the AEM technique provides a means for evaluating this p otential.