Nitrogen dynamics and red pine growth following application of pelletized biosolids in Massachusetts, USA

Pelletized biosolids from municipal wastewater treatment were applied to a thinned red pine plantation to determine if there were treatment levels that could produce a fertilization growth response without resulting in unacceptable nitrate leaching. The pellets (total nutrient concentrations of 4.4% N, 1.4% P, 0.2% K) were applied at four levels (0, 200, 400, 800 kg/ha total N). Only 26% of labile organic N in the pellets was mineralized in the first year after application. Foliar N increased with increasing application rate, but other nutrients were unchanged. Red pine basal area growth was unchanged with low and medium levels, but decreased to 50% of control plots with the highest level. A decrease in foliar K/N ratio resulting from high N uptake with little additional K is hypothesized as the cause for the growth decline. The highest treatment level resulted in lysimeter nitrate-N concentrations increasing to 2 mg/L in the first year and 9 mg/L in the second, returning to control levels in the third; no increase occurred in other treatments. These results contrast with those found with liquid sludge applications, in which nearly all N mineralization and the highest nitrate leaching rates occurred in the first year. The slower release of inorganic N from pellets over 2 years may allow higher total N application rates without causing high nitrate leaching.