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TECHNICAL REPORTS

Waste Management

Controlled Application Rate of Water Treatment Residual for Agronomic and Environmental Benefits

^a Crop and Soil Science Dep., 512 Plant and Soil Science Bldg, Michigan State Univ., East Lansing MI 48824
^b Soil and Water Science Dep., P.O. Box 110510, Univ. of Florida, Gainesville, FL 32611-0510

^* Corresponding author (ooladeji{at}msu.edu).

Received for publication March 30, 2007. Water treatment residuals (WTR) are useful soil amendments to control excessive soluble phosphorus (P) in soils, but indiscriminate additions can result in inadequate control or excessive immobilization of soluble P, leading to crop deficiencies. We evaluated the influence of application rates of an Al-WTR and various P-sources on plant yields, tissue P concentrations, and P uptake and attempted to identify a basis for determining WTR application rates. Bahiagrass (paspalum notatum Fluggae) was grown in a P-deficient soil amended with four P-sources at two application levels (N- and P-based rates) and three WTR rates (0, 10, and 25 g kg^–1 oven dry basis) in a glasshouse pot experiment. The glasshouse results were compared with data from a 2-yr field experiment with similar treatments that were surface applied to an established bahiagrass. Soil P storage capacity (SPSC) values increased with application rate of WTR, and the increase varied with sources of P applied. Soil soluble P concentrations increased as SPSC was reduced, and a change point was identified at 0 mg kg^–1 SPSC in the glasshouse and the field studies. A change point was identified in the bahiagrass yields at a tissue P concentration of 2.0 g kg^–1, corresponding to zero SPSC. Zero SPSC was shown to be an agronomic threshold above which yields and P concentrations of plants declined and below which there is little or no yield response to increased plant P concentrations. Applying P-sources at N-based rates, along with WTR sufficient to give SPSC value of 0 mg kg^–1 SPSC, enhanced the environmental benefits (reduced P loss potential) without negative agronomic impacts.

Abbreviations: Al_ox, oxalate-extractable aluminum • Al-WTR, aluminum water treatment residual • APSC, amendment phosphorus storage capacity • DM, dry matter • DPS, degree of phosphorus saturation • Fe_ox, oxalate-extractable iron • PAN, plant-available nitrogen • P_ox, oxalate-extractable phosphorus • PSR, phosphorus saturation ratio • SPSC, soil phosphorus storage capacity • STP, soil test phosphorus • TSP, triple superphosphate • WEP, water-extractable phosphorus • WTR, water treatment residuals