Sustainable Rates of Sewage Sludge for Dryland Winter Wheat Production II. Production and Income

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.