Estimation of N and P in Florida Dairy Wastewater for Silage Systems

Manure management is an integral concern of Florida dairymen. Wastewater from nine dairy sprayfields on seven north Florida dairies with overhead sprinkler or gun irrigation facilities was collected biweekly from early September 1992 to Janu­ ary 1993. Samples were taken from the pump area of either anaerobic lagoons or settling ponds, rainfall, and from effluent plus rainfall in sprayfields. All unfiltered and filtered samples were analyzed for total Kjeldahl N, NH4, NO3 -, and P. Con­ centrations of different forms of N and for P were site-specific, likely due to differences in wastewater and manure handling and disposal systems and herd sizes. Based on effluent analysis, dairies were applying large and differential amounts of solids through their irrigation systems to sprayfields. This was confirmed by filtered samples, accounting for only as much as 55% of the total Kjeldahl N in unfiltered samples for one dairy. Filtered NH4 levels were 41% to 85% of total Kjeldahl in un­ filtered samples. Based on literature, it was estimated that most dairies were under-fertilizingexisting crops for N and applying slightly above or about the right amount of P. Essentially no nitrate was produced in dairy effluent that was applied to the sprayfields.