Agronomy and Horticulture Department


Date of this Version

March 2002


Published in Soil Sci. Soc. Am. J. 66:531–543 (2002). Copyright © 2002 by the Soil Science Society of America. Used by permission.


We quantified effects of anaerobically digested sewage sludge (bio- solids) on yield, N use efficiency, and soil NO3 over a period of 4 yr. Field experiments with five biosolids rates and six N rates were conducted at two sites on a silty clay loam soil: one with irrigated maize (Zea mays L.) and another site with rainfed sorghum (Sorghum bicolor L.). Biosolids rates for achieving maximum yields in the year of application were 62 Mg ha-1 (441 kg organic N ha-1) on irrigated maize and 36 Mg ha-1 (257 kg organic N ha-1) on rainfed sorghum. At those rates, the increase in relative yield (RY) was 33% in the year of application, 21% in the second year, 14% in the third year, and 9% in the fourth year. Approximately 40, 20, 10, and 5% of the total biosolids-N was recovered by the crops in the first, second, third, and fourth year, respectively. In irrigated maize, use efficiency of biosolids-N decreased with increasing biosolids rate, but was similar to that of fertilizer-N. In rainfed sorghum, use efficiency of biosolids- N was lower than that of fertilizer-N. Little NO3 accumulated in soil when biosolids were applied at the recommended rate, but application in excess of that required for maximum yield increasedNO3 accumula- tion in soil. The cumulative N fertilizer value of a biosolids application at the optimal rate was $136 ha-1 for maize and $68 ha-1 for sorghum. Biosolids had a total fertilizer-N replacement value of $1.9 to 2.2 Mg-1 biosolids. Recommendations for biosolids use should be based on the total N input and its cumulative plant recovery and leaching potential across a 4-yr period.