Surface-Applied Biosolids Enhance Soil Organic Carbon and Nitrogen Stocks but Have Contrasting Effects on Soil Physical Quality

Table 1

Minimum, maximum, and mean concentrations for selected biosolids constituents and total loading of dry matter (DM) and by constituent based on treatment rate, application area, and years of application (adapted from [17]).

Biosolids application rate (Mg ha^−1 yr^−1)					20	40	60	20
Application duration (yr)					8	8	8	20^†
Treatment area (ha)					20	36	49	14
Biosolids constituent^‡	Unit	Min	Max	Mean	Total loading, Mg (DM) ha^−1
Total solids	%	15.2	19.3	17.6	160	320	480	400
Total organic C	kg Mg^−1	296.1	321.6	307.9	49.3	98.5	147.8	123.1
Total Kjeldahl N	kg Mg^−1	27.8	67.9	52.1	8.3	16.7	25.0	20.8
Total P	kg Mg^−1	13.4	29.1	16.1	2.6	5.2	7.7	6.4
K	kg Mg^−1	0.2	3.4	1.5	0.2	0.5	0.7	0.6
pH	—	8.2	8.7	8.5	—	—	—	—
Electrical conductivity	mS cm^−1	2.7	3.9	3.5	—	—	—	—

Annual applications in this treatment reduced to biennial applications of 5 Mg ha⁻¹ yr⁻¹ in 2007.
^‡Environmental Protection Agency (EPA) or Standard Methods (SM) protocols used to quantify each constituent, in order listed: SW846 9060A; EPA 351.2; SM 4500-P BE; EPA 6020; SM 4500-H; EPA 9045D; SM 2540G.