POTENTIAL BENEFITS OF LAND APPLYING BIOSOLIDS IN EASTERN NEBRASKA

Two four year field experiments were conducted to determine the optimal application rate of the City of Lincoln's anaerobically digested biosolids for irrigated corn and dryland sorghum; to quantifiy the nitrogen (N) value of biosolids; to determine the residual value of biosolids; and to evaluate the environmental impact associated with land application of biosolids. Five rates of biosolids were applied in each year to separate areas so that no area received more than one application. Yield and nutrient uptake were measured and compared to yields attained with N fertilizer. The optimal biosolids rate was 28 tons acre−1 for irrigated corn and 16 tons acre−1 for dryland sorghum. On average, at the optimal biosolids rate yields were increased by 33% in the first year and 21%, 14%, and 9% in the second, third and fourth years respectively. The cost of N fertilizer required to get a similar yield increase was 31 acre−1 for corn and 17 acre−1 for sorghum the first year. Over four years a one time application of biosolids resulted in yields equivalent to 57 and 31 acre−1 of N fertilizer for corn and sorghum respectively. At or below the optimal biosolids rate very little nitrate accumulated. At the irrigated corn site nearly a third of the accumulated nitrate, 180 lbs-N acre−1, leached to the four foot soil depth in less than one year after biosolids were applied when the biosolids were applied at twice the optimal rate. At the dryland location 25% of the accumulated nitrate, 55 lbs N acre−1, leached to the four foot soil depth in less than one year after twice the optimal rate of biosolids was applied. More phosphorus is applied than typical agronomic crops utilize when biosolids are applied at rates high enough to supply N. Soil phosphorus (P), Bray-P, levels were built up to near 300 ppm, nearly twenty times the critical level of 15 ppm, when 36 dry tons (280,000 gallons) of Lincoln's biosolids were applied over a 16 year period. However at the same location cadmium, copper, lead, nickel, and zinc build up was only slightly higher than an average great plains soil. All of the metals regulated by the EPA remained far below even the most stringent of international soil standards. Thus under current wastewater treatment and land application practices in Nebraska the greatest environmental concern for land application of biosolids is proper nutrient management and not metal accumulation.