Anaerobically digested liquid sludge was applied during two separate periods to plots in a mixed hardwood forest. High treatment plots received 26.96 metric tons/ha total solids and 3,034 kg/ha N loadings during the two applications, and low treatment plots received approximately half these loadings. Percolate samples collected at the 15-cm depth contained a maximum of 290 mg/liter NO3--N in the high treatment and 194 mg/liter NO3--N in the low treatment. Maximum monthly levels of NO3--N in percolate sampled at the 120-cm depth lagged 6 months behind peak levels at the 15-cm depth. Calculated average active transmitting soil porosity (Pact), based on field water budget data over this 6-month period, ranged from 15 to 22%. A CSMP computer simulation model based on a solution to the convection diffusion equation estimated the average Pact to be 15%. Since these data indicate that 27 to 50% of the pores may be stagnant, this suggests that soluble NO3--N was being channeled through interconnected macropores in the soil profile.
Soil Science Society of America. Journal / Vol. 43, No. 2, pp.278-282