2.2. Nutrient treatments
Two nutrient application rates were used. The high rate
of nutrient application was selected to approximate the maximum
allowable plant available nitrogen (PAN) (300 kg PAN ha−1)
from biosolids. The lower application rate was similar to that
which a producer might use in annual applications of MF (about
150 kg N ha−1). A mixture of triple super phosphate (TSP) and diammonium
phosphate were used as the MF. The MF mixture was
blended to match the estimated PAN and P nutrient content of
the low rate of biosolids (Tables 2 and 3). Nutrient analysis of the
biosolids was used to estimate the biosolids application rate (15.6
and 7.8 Mg ha−1 on a dry basis for high and low rates, respectively).
The anaerobically digested, dewatered municipal biosolids used
in this study were Class B biosolids (Miles et al., 1995) and were
obtained from the Southwest Wastewater Treatment Plant in
Springfield, MO. PAN of the biosolids was estimated by multiplying
the organic N fraction of the biosolids by the first year mineralization
rate (USEPA, 1994b) and then adding NH4-N after correction
for volatilization reductions (Arnold et al., 1994), and adding nitrate
nitrogen (NO3-N) as follows:
PAN = 0.2(A) + 0.7(NH4-N) + (NO3-N)
where A is equal to the organic N fraction {[total Kjeldahl nitrogen
(TKN)]–[NH4-N]–[NO3-N]} of the biosolids.