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TECHNICAL REPORTS

Waste Management

Soil Nitrate Nitrogen Dynamics after Biosolids Application in a Tobosagrass Desert Grassland

^a Campo Experimental "La Campana", Instituto Nacional de Investigaciones Forestales Agrícolas y Pecuarias (INIFAP), Chihuahua, Chih., México 31100
^b Department of Range, Wildlife, and Fisheries Management, College of Agricultural Sciences and Natural Resources, Texas Tech University, Lubbock, TX 79409

^* Corresponding author (david.wester{at}ttu.edu)

Received for publication February 21, 2005. Dormant-season application of biosolids increases desert grass production more than growing season application in the first growing season after application. Differential patterns of NO₃–N (plant available N) release following seasonal biosolids application may explain this response. Experiments were conducted to determine soil nitrate nitrogen dynamics following application of biosolids during two seasons in a tobosagrass [Hilaria mutica (Buckl.) Benth.] Chihuahuan Desert grassland. Biosolids were applied either in the dormant (early April) or growing (early July) season at 0, 18, or 34 dry Mg ha^–1. A polyester–nylon mulch was also applied to serve as a control that approximated the same physical effects on the soil surface as the biosolids but without any chemical effects. Supplemental irrigation was applied to half of the plots. Soil NO₃–N was measured at two depths (0–5 and 5–15 cm) underneath biosolids (or mulch) and in interspace positions relative to surface location of biosolids (or mulch). Dormant-season biosolids application significantly increased soil NO₃–N during the first growing season, and also increased soil NO₃–N throughout the first growing season compared to growing-season biosolids application in a year of higher-than-average spring precipitation. In a year of lower-than-average spring precipitation, season of application did not affect soil NO₃–N. Soil NO₃–N was higher at both biosolids rates for both seasons of application than in the control treatment. Biosolids increased soil NO₃–N compared to the inert mulch. Irrigation did not significantly affect soil NO₃–N. Soil NO₃–N was not significantly different underneath biosolids and in interspace positions. Surface soil NO₃–N was higher during the first year of biosolids application, and subsurface soil NO₃–N increased during the second year. Results showed that biosolids rate and season of application affected soil NO₃–N measured during the growing season. Under dry spring–normal summer precipitation conditions, season of application did not affect soil NO₃–N; in contrast, dormant season application increased soil NO₃–N more than growing season application under wet spring–dry summer conditions.

Abbreviations: IM, inert mulch