EFFICIENCY OF PHOSPHORUS UTILIZATION BY ALFALFA FROM MANURE AND SUPER-PHOSPHATE

Alfalfa grown in soil treated with superphosphate removed a higher percentage of the added P than alfalfa grown in soil treated with manure. Alfalfa grown in manured soil had the higher P utilization efficiency, as measured as yield increase per unit increase in P removed. This was due in part to more luxury consumption of P by the early cuttings on the superphosphate treatment. The P in feedlot manure was released more slowly for plant uptake and the P level remained adequate for a longer period. Apparently, microbial activity is important in the slow release of manure P. This was probably due to the increase in microbial activity as a result of the added energy source. P from feedlot manure carries over from year to year becomes available with time.