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ARS Home » Pacific West Area » Kimberly, Idaho » Northwest Irrigation and Soils Research » Research » Publications at this Location » Publication #223241
Title: Organic Waste Nitrogen and Phosphorus Dynamics Under Dryland Agroecosystems

Author
item Ippolito, James
item BARBARICK, KEN - COLORADO STATE UNIVERSITY

Submitted to: Proceedings of the Idaho Nutrient Management Conference
Publication Type: Proceedings
Publication Acceptance Date: 2/22/2008
Publication Date: 3/4/2008
Citation: Ippolito, J.A., Barbarick, K. 2008. Organic waste nitrogen and phosphorus dynamics under dryland agroecosystems. Proceedings of the Idaho Nutrient Management Conference. p. 13-18.

Interpretive Summary:

Technical Abstract: Organic waste beneficial-use programs effectively recycle plant nutrients when applied at agronomic rates. Plant-nutrient availability, transport, and fate questions have arisen when organic wastes such as biosolids have been applied to dryland agroecosystems. What is the N-fertilizer equivalency of biosolids? What is the N mineralization rate of biosolids over periods of excess moisture or drought, and over long periods of time? Would biosolids, applied at an agronomic N rate for dryland winter wheat (Triticum aestivum L.), oversupply P? If over-application occurred, what would the repercussions be in terms of excess soil P? Our objectives were to determine: biosolids N fertilizer equivalency; biosolids N mineralization during years of above and below average precipitation, and long-term N mineralization; which soil P phases dominate following years of biosolids application; and the potential increased environment risk of P when applying an agronomic N rate or excessive rate of biosolids. To address questions related to N dynamics, we utilized research results collected between 1993 and 2004 from a site in Eastern Colorado which received 0, 1, 2, 3, 4, and 5 dry tons biosolids per acre. To address questions related to P dynamics, results collected between 1982 and 2003 from a second Eastern Colorado site which received 0, 3, 6, 12, and 18 dry tons biosolids per acre were used. During years of above-average and below-average precipitation, first-year biosolids N mineralization rates were estimated at 25-32% and 21-27%, respectively; long-term first-year mineralization rate ranged between 27-33%. Based on wheat-grain N uptake, we found that an application rate of 1 dry ton biosolids per acre supplied about 20 lbs N per acre. Based on the Colorado P index risk assessment, biosolids applied at agronomic N rates would not force producers to alter application strategies. However, based on this risk assessment, biosolids over-application would force land application to be based on crop P requirements. Previous results showed a minimum of 3 cropping cycles were necessary to reduce soil P concentrations to levels considered less apt in causing environmental degradation. A future reduction in water availability may force some Idaho agricultural land to shift from irrigated to dryland conditions. And, coupled with the increased production of dairy waste, land applicators will need to find new means to protect natural resources under dryland conditions. Results from our studies can help improve nutrient use efficiency and minimize environmental risk associated with dryland organic waste land application.