Biosolids and Dairy Manure as Nitrogen Sources for Prairiegrass on a Poorly Drained Soil

Abstract

Accurate prediction of plant-available N release from municipal and agricultural byproducts is needed to optimize crop yields and minimize nitrate leached to groundwater. We conducted a 4-yr study to determine plant-available N release from two byproducts: dewatered biosolids (stabilized solids from municipal wastewater treatment) and dairy manure. The Buckley loam soil (fine-loamy, mixed, nonacid, mesic Typic Humaquepts) at our study site had a perched water table 0 to 24 in. below the 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. willildnowii Kunth] for 2 yr (1991-1992). Plant-available N released from biosolids or manure was measured for two additional years (1993-1994) after we terminated application. 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 1991-1992 increased soil nitrate recovered after a summer of chemical fallow in 1994. The additional nitrate recovered in 1994 represented approximately 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 and manure use must account for the residual effects of previous applications.