Residuals and Manure Management for Environmental and Agronomic Benefits Olawale O. Oladeji Soil and Water Science Department University of Florida

Residual Application Rates  Meet N needs of plants (N-based) and avoid excessive N that can pollute the ground water.  N-based rates often provide and load soils with excessive P  Excess P:  Not harmful to plants  Potential environmental impact

Phosphorus Loss  Sandy soils of Florida sorb P poorly and surround P sensitive water bodies

Water Treatment Residuals (WTRs)  Generated with Al and Fe coagulants  Mostly Al and Fe hydroxides  High affinity for phosphorus !!!

WTR Rates  Land application of WTRs could lead to excessive immobilization of soil P and Al toxicity  Negative impact of WTRs calls for best management for environmental and agronomic benefits Excess WTR Inadequate WTR Deficiency (P loss) Deficiency (Excessive immobilization)

Soil Test Methods  A good soil test could be a tool to identify environmental and agronomic thresholds to arrive at optimum rates of WTRs and P sources.  Conflicting results from the use of conventional soil test methods (e.g., Mehlich 1) in studying soils receiving WTR call for identifying suitable soil test methods.

Hypotheses I. There exist suitable soil test methods for P bioavailability in soil receiving organic sources of P and WTRs. II. (1)P-based rates of different organic sources of P without WTR optimize P uptake. (2)N-based rates of different organic sources of P with WTR optimize P uptakes. III. Amendment rates selected in (II) that optimize P uptake also minimize leaching and runoff P.

Objectives  Determine suitable soil test methods for P bioavailability in soils amended with different P sources and WTR.  Determine the rates of WTR and organic P sources that optimize plant P uptake while minimizing environmental P hazards.  Evaluate the impacts of selected amendments rates (WTR and organic P sources) on leaching and runoff P.  Validate the expected impacts of selected amendment (WTR and organic P sources) rates on P uptake and P loss in field settings.

Experiment I: Glasshouse Study Objectives:  Determine suitable soil test methods for P bioavailability in soil treated with different organic sources of P in the presence and absence of WTR  Determine the rates of organic sources of P (amendments), with and without WTR, that optimize P uptake Design:  4X2X3 factorial experiment plus 1 control in randomized complete block with 3 replicates Factors:  4 P Sources (Poultry manure, Boca Raton Biosolids, Pompano Biosolids, TSP)  2 P Sources rates (N- and P-based)  3 WTRs rates (0, 1.0 and 2.5% oven dry basis) Test plants: Bahiagrass (Paspalum notatum Fluggae) follow by Fescue grass (Festuca ovina “Glauca”)

Glasshouse Experiment Data to be collected:  Total P and soil test P (using selected extraction methods: Mehlich-1, Water extractable P, Fe strip P)  Plant dry matter yield.  Plant P content and uptake.

Experiment II: Rainfall Simulation Objectives:  Evaluate impact of organic sources of P on leaching and runoff P  Determine the effect of WTR placement on leaching and runoff P  Determine the environmental threshold for P Design: 4X2X2X2 factorial experiment plus 1 control in randomized complete block with 3 replicates Factors:  4 P Sources: Poultry manure, Boca Biosolids, Pompano Biosolids, TSP  2 P Sources rates :N- and P-based  2 WTRs rates : 0, and 1.0%  2 placement methods: Surface and Mixed

Rainfall Simulation  Runoff boxes (100cm*20cm*7.5cm)  Surface slope (3 degree)  Simulated rain 7.1cm hr -1  Three rain events at 2-days interval  Runoff collected for 30 minutes (Leachate also collected) Rainfall Simulator

Rainfall Simulation Data to be collected:  Quantity of runoff and leachate  Total runoff and leaching P  Runoff and leaching dissolved P

Expected Results  N based rates with WTR and P based rates expected to give soil test P (STP) below the change point (environmental threshold)  N based rate without WTR is expected to give STP and RDP above the change point  Environmental threshold STP is expected to be about three times agronomic optimum Agronomic threshold Environmental threshold Change point Soil test P AE = ~3A RDP (mgL -1 )

Experiment III: Field Experiment Field validation of impacts of selected rates and sources of P and WTR on P loss and uptake Design: 4X2X3 factorial experiment plus 1 control in randomized complete block with 3 replicates Factors:  4 P Sources: Poultry manure, Boca Biosolids, Pompano Biosolids, TSP  2 P Sources rates :N- and P-based  2 WTRs rates (0, and 1.0%) Test plant: Bahiagrass

Field Experiment Data to be collected:  Runoff and leaching P  Plant dry matter yield  Plant P uptake  Total P and soil test P using selected extraction methods (Mehlich-1, Water extractable P, Fe strip P); oxalate extractable P, Al, Fe,).

Preliminary Results  WEP and ISP are better correlated with P uptake than Mehlich-1  WEP and ISP are potential soil tests for P in WTR treated soils.

Preliminary Results  Potential P loss (readily desorbable P) is lower in WTR treated soil as indicated by the WEP and ISP With WTR Without WTR

Preliminary Results Amendments Rates DPS (%) ∆ DPS with WTRWithout WTR ManureN-based Boca Pompano79386 TSP ManureP-based94940 Boca42824 Pompano94536 TSP  DPSox = (Ox-P) X 100 α(Ox-Fe + Ox-Al)

Preliminary Results  Treatments without WTR have %DPS ox above the change point.  Treatment with WTR have %DPS ox below the change point (environmental threshold). calculated using oxalate extraction (DPSox) for soil receiving different P sources with and without WTR %DSP(OX) WEP (mg/kg) With WTR Without WTR Control Nair et al., 2004

Impact of WTR on Soil and Plants  WTR addition lowers DPS ox without significantly impacting the plant

THANKS