The application of sewage sludge to agricultural land has become the major method of sludge disposal in the USA. Therefore, the long‐term impact of sludge application to the soil environment must be investigated in order that proper loading rates are employed. Thus, a field study was initiated in 1982 in Adams County, Colorado, with the goal of evaluating the effects of the Littleton/Englewood, CO, sewage sludge on soil N, Zn, Cu, Cd, Ni, and Pb levels in a dryland hard red winter wheat (Triticum aestivum L., ‘Vona’)‐fallow management system compared to commercial NH4NO3 fertilizer. This report covers soil data for the last three years of this 5‐yr study where sludge rates ranged from 0 to 18 dry ton/acre, and N fertilizer rates ranged from 0 to 120 lb N/acre. Sewage sludge application resulted in increased soil NO3‐N levels at harvest compared with the N fertilizer for all depths sampled and each year reported. Mean NO3‐N levels of the surface 8 in. for the sludge and N fertilizer treatments ranged from 10 to 32 ppm and from 2 to 9 ppm, respectively. The soil NO3‐N in the root zone (considered to be about 6 ft for wheat) data showed that three sludge applications, of 12 ton/acre resulted in significantly higher NO3‐N levels throughout the root zone compared with the control or 50 Ib N/acre. A loading rate of 3 ton/acre resulted in significantly greater NO3‐N than the control at the 0 to 8 in. and 24 to 35 in. depths. Sludge application, at all loading rates tested, resulted in significantly increased NH4HCO3‐diethylenetriaminepentaaceticacid (AB‐DTPA) extractable concentrations of Zn, Cu, Cd, Ni, and Pb compared to the control in the surface 8 in. of the soil. Because of the potential for NO3‐contamination of groundwater (and metal build‐up in the soil) by the higher sludge loading rates, a loading rate of 3 ton/acre is recommended as the maximum safe loading rate for his dryland wheat system.
The increased production of sewage sludge in the USA has led many municipalities to consider the application of sludge to agricultural land as a feasible means of sludge disposal and nutrient recycling. Therefore, a long‐term field study was initiated in 1982 in Adams County, Colorado, with the objective of evaluating the effects of sewage sludge on, gross income, yields, grain protein, and elemental content of dryland hard red winter wheat (Triticum aestivum L., ‘Vona’) compared to commercial NO4NO3 fertilizer. This report covers plant data for the last three years of this 5‐yr study where sludge rates ranged from 0 to 18 dry ton/acre, and N fertilizer rates ranged from 0 to 120 lb N/acre. Sludge application has produced greater gross income than N fertilizer treatments primarily due to the protein premiums paid for high protein grain. Application of the 3 ton/acre sludge rate resulted in an average of $45/acre/year increase in income compared to the commonly used N rates of 50 to 60 lb N/acre. In two of the three years, neither the sludge nor the N fertilizer treatments resulted in significant yield responses. The mean grain yields of the sludge and N fertilizer treatments ranged from 50 to 71 bu/acre and 51 to 64 bu/acre, respectively, while protein content ranged from 13.3 to 15.5% and 11.0 to 12.7%, respectively. In addition, sludge application has resulted in greater soil NH4‐N and NO3‐N compared to the N fertilizer treatments at boot stage over the last three years. However, because of the potential for NO3− contamination of groundwater due to oversupply of N (and the potential for metal build‐up in the soil) by the 12 and 18 ton/acre rates, the lower sludge rate of 3 ton/acre is recommended for this dryland wheat production system. Grain levels of P and Zn have been increased by sludge application while the concentrations of Cd, Ni, and Pb have remained very low.
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