BIOSOLIDS AND DAIRY MANURE AS NITROGEN-SOURCES FOR PRAIRIEGRASS ON A POORLY DRAINED SOIL

Accurate prediction of plant-available N release from municipal and ag ricultural byproducts is needed to optimize crop yields and minimize n itrate leached to groundwater. We conducted a 4-yr study to determine plant-available N release from two byproducts: dewatered biosolids (st abilized solids from municipal wastewater treatment) and dairy manure, The Buckley loam soil (fine-loamy, mixed, nonacid, mesic Typic Humaqu epts) at our study site had a perched water table 0 to 23 in, below th e surface from mid-November through mid-May, Biosolids and manure were surface-applied to established prairiegrass [Bromus unioloides (Willd .) H.B.K. cv. Grasslands Matua; syn, B, willdenowii Kunth] for 2 yr (1 991-1992), Plant-available N released from biosolids or manure was mea sured for two additional years (1993-1994) after we terminated applica tion, Cumulative apparent N recovered by grass harvest for 1991, 1992, and 1993 was 77, 74, and 65% for urea; 27, 29, and 38% for biosolids; and 17, 28, and 36% for manure, Biosolids or manure applied in 1991-1 992 increased soil nitrate recovered after a summer of chemical fellow in 1994. The additional nitrate recovered in 1994 represented approxi mately 6% of the biosolids or manure N applied in 1991-1992. Our study demonstrated increased soil N mineralization rates following 2 yr of biosolids or manure application, Farm management plans for biosolids a nd manure use must account for the residual effects of previous applic ations.