Dairy Manure-component Effects on Phosphorus Release from Sandy Soils M. S. Josan*, V. D. Nair, and W. G. Harris. Soil and Water Science Department, Gainesville, FL (josanmd@ufl.edu) Introduction Materials and Methods Results and Discussion Dairy manure accumulation in soils can increase potential for phosphorus (P) loss to surface waters via erosion or subsurface drainage. Phosphorus in heavily manure-amended sandy soils can be labile even years or decades after manure input cease. Stability of manure-derived forms of P is an especially relevant environmental concern in sandy soils. Dairy manure-amended sandy soils typically contain large amounts of Ca and P in both solid and solution phases, with accompanying moderately higher pH (Nair et al., 2003) than native, non-impacted soils. The conditions thermodynamically favor formation of relatively stable Ca-P minerals (Lindsay, 1979), but release of P from these soils can be greater than predicted from the solubility of the minerals (Wang et al., 1995). High Mg concentrations in soil solution of heavily manure-amended soils suggest that Mg, in addition to Ca, could control P release via a sparingly soluble Mg-P phase (Nair et al., 1995; Josan et al., 2005). Knowledge of manure-derived components and their associations with P is pertinent to nutrient management, particularly for sandy soils with minimum P sorbing components. Table 2. Characteristics of active and abandoned manure-amended soils, and minimally manure-impacted soils Table 3. Speciation Data from Column Leachates EXPERIMENT 1. SOIL & MANURE CHARACTERIZATION Manure-amended sandy soils (Ultisols and Spodosols) from 4 active, and 4 abandoned dairies, 4 native soils; 4 dairy manure samples from Florida Chemical characterization: pH, EC, Total-P, Total-Ca, Mg, Fe and Al. Particle size fractionation and mineralogical analysis EXPERIMENT 2: P RELEASE & ELEMENTAL ASSOCIATIONS Approach A: Repeated Water Extraction 1:10 soil:deionized water pH, EC, soluble reactive phosphorus (SRP), Ca, Mg, Na, K, Fe and Al. Approach B: Selective Dissolution Soil samples were extracted with 1.0 M NH4Cl (2 h) adjusted to pH 7.0 from 1 to 10 times before being extracted with 0.1 M NaOH(17 h), and finally with 0.5 M HCl (24 h) at 298 K using a 1:10 soil:solution ratio. Extracts were analyzed for both inorganic-P (Pi) and total dissolved P (TDP); and for Ca, Mg, Fe and Al using atomic absorption spectroscopy. Approach C: Solid State Assessments X-ray Diffraction of untreated clays from manure-amended soils Ashed and whole dairy manure analyses: manures were ashed at 550oC for 5 h and scanned by XRD. Scanning Electron Microscopy (SEM) Imaging and Energy Disoersive Spectroscopy (EDS) Analyses Electron Microprobe Microanalyses of whole silt + clay in soils EXPERIMENT 3: CHEMICAL SPECIATION STUDY Leaching study: 4 active and 4 abandoned soils, 2 replications for each soil type (10 columns) Columns were packed using with 707g of soil (25% moisture content and 1.2 g cm-3 bulk density) Leached by adding 283 mL of DI water over 2-h period, allowed to drain for 16 h Leachates collected in 500-mL beakers and analyzed for pH, EC, metals (Ca, Mg, Na, K, Fe, Si and Al), Cl, nitrates, ammonium, sulfate, dissolved organic carbon and inorganic carbon. V-MINTEQ used for speciation calculations. Parameters used: Charge Balance 30%, Davis equation for activity corrections, Gaussian model for dissolved organic matter, and ionic strength was calculated from EC measurements. Ionic strength = 0.013 x EC. EXPERIMENT 4: INCUBATION STUDY Manure-derived solids obtained: Particle size separations of soils, Carbonate and organic matter removed from clays Incubation solutions: Control -Average leachate concentrations (Table 1), No Mg, Si, and DOC Mg treatment – Control + Mg† (179 mg L-1), No Si and DOC Si treatment – Control + Si† (23 mg L-1), No Mg and DOC DOC treatment – Control + DOC† (427 mg L-1), No Mg and Si Four incubation treatments with four replications: In the presence and absence of solids; 100 mg of solids were incubated in 50 mL of solution for 20 weeks with initial pH 6.8 Solutions were monitored weekly for pH and water levels: 1 mL samples were pipetted and diluted 10 times and filtered through a 0.45 µm filter Solution analyses: P by ascorbic acid colorimetry; Ca, Mg, Fe, Al using atomic absorption spectroscopy, DOC was measured by TOC-5050A, Shimadzu Solid state assessments: X-ray diffraction (XRD), and energy dispersive spectroscopy (EDS) Statistical analyses: Non-parametric statistical analyses (Kruskal-Wallis Test) at p=0.05 †Average leachate concentrations for the species Mineral Phase Formula Active Abandoned (SI = log IAP - log Ksp) Struvite (NH4MgPO4·6H2O) -0.1 to -2.5 -0.9 to -2.3 Farringtonite Mg3(PO4)2 -0.2 to -3.5 -1.1 to -3.8 Newberryite MgHPO4·3H2O -0.3 to -2.3 -0.4 to -9.1 Monetite CaHPO4 -1.3 to 0.3 -0.1 to 0.7 Brushite CaHPO4·2H2O -1.6 to 0.0 -0.7 to 0.5 Hydroxyapatite [Ca5(PO4)3 (OH)] 10 to 13 Both active and abandoned dairies have high total-P, total Ca and Mg concentrations as compared to native soils (Table 2). Most of the soluble Ca-P minerals were supersaturated, All the Mg-P minerals were either under saturated or near saturation. (-1<SI<0) appropriate for Saturation (Table 3). Soil pH EC Total P Total Ca Total Mg Total Fe Total Al dS m-1 ------------------------mg kg-1------------------- ACS † 7.5a 0.64a 2334a 7086a 1292a 918a 2550a ABS†† 6.7a 0.50a 2091a 11082a 603b 518a 1223a NIS††† 5.3b 0.15b 104b 301b 25c 430a 1138a †ACS= Active dairy soil; ††ABS = Abandoned diary soil; †††NIS = non-impacted soil * Statistical significance for different letters (a, b, c) read vertically Fig. 1 Soil sampling at a heavy manure-impacted site Active Dairies P concentrations were significantly lower (p<0.05) for the Mg treatment than for the control from the 1st week to the 10th week of incubation; however after the 20th week, there was no significant difference between the P concentrations in the Mg treatment and the control. The sharp decline in the P concentrations in the 1st through 10th week coincided with the formation of precipitates in both the control and the Mg treatment solutions. Abandoned Dairies Release of P was more closely associated with Mg than Ca in water extractions Both active & abandoned dairy soils release similar amounts of Mg and P Mg-P and Ca-P associations occur in manure and manure-amended soils Most Ca-P minerals were near saturation ; HAP an exception Mg-P minerals under-saturated or near saturation Mg inhibited HAP formation, enabled brushite formation DOC – No Ca-P mineral formed Solids-Inhibit Ca-P stabilization Si – No inhibition of Ca-P crystallization Fig. 3 Soluble reactive phosphorus (SRP) concentration with sequential water extraction Fig. 3 Fig. 9 P concentrations in the presence of Mg during 20 weeks (wk) of incubation (p<0.05) and XRD pattern of the precipitate in the Mg solution after 20 weeks of incubation. Hypotheses Active and abandoned dairy manure-amended soils release comparable amounts of P because solution P is controlled by sparingly-soluble Mg and/or Ca phosphate phases that require many years for depletion. Concentrations of P, Ca, and Mg are spatially correlated in solid manure and manure-amended soil samples. Activities of DOC, Mg and Si in soil solution of manure-amended soils are sufficient, jointly or separately, to inhibit crystallization of stable Ca-P forms, thus leading toward high P release from the soils. Figs. 4 & 5 Relationship between sequential water extracting Ca and Mg concentration and SRP for active and abandoned dairy manure-impacted soils respectively. Fig. 4 Fig. 8 EDS dot maps of dairy manure and dairy manure-amended soil clay showing an association of P-Ca-Mg (left) and P-Ca (right). (scale 20 μm). Fig. 2 XRD Analyses Objectives Overall objective: To understand the role of manure-derived components, Mg, Si, and dissolved organic carbon (DOC), in maintaining high P solubility in active and abandoned dairy manure-amended sandy soils. Specific objectives: Assess the release of P, Ca and Mg in soil solutions of dairy manure-amended soils. Study the associations of P, Ca, and Mg in dairy manure and manure-amended soils using solid state assessments. Study the effects of Mg, Si and DOC on Ca-P crystallization using average concentrations of the species found in manure-amended soil leachates. Fig. 5 Table 4. Total dissolved phosphorus (TDP) as a function of Ca+Mg in repeated 1.0 M NH4Cl extractions (Data from 1st extraction omitted) Dairy Type Soil ID N Regression Equation r2* Active ACS-1 9 TDP = 0.107(Ca+Mg) - 0.912 0.895†† ACS-2 TDP = 0.246(Ca+Mg) - 0.226 0.993†† Abandoned ABS-1 TDP = 0.042(Ca+Mg) + 2.324 0.536† ABS-2 TDP = 0.047(Ca+Mg) + 0.831 0.604† TDP = 0.624Ln(Ca+Mg) + 1.488 0.703†† TDP = 0.421Ln(Ca+Mg) + 0.523 0.793†† References Fig. 6 Electron probe microanalyses of active (6-9a & 6-9b) and abandoned dairy (6-9c & 6-9d) manure-amended dry sieved (45µm) silt + clay .**significant at p<0.05. Fig. 7 X-ray diffraction patterns of oven dried and ashed dairy manures (3) showing the presence of Mg-Ca Whitlockite (Mg-Ca phosphate) Josan, M.S., V.D. Nair, W.G. Harris, and D. Herrera. 2005. J. Environ. Qual. 34:184-191. Lindsay, W.L. 1979. Chemical Equilibria in Soils. Wiley-Interscience, New York. Nair, V.D., D.A. Graetz, and K.M. Portier. 1995. Soil Sci. Soc. Am. J. 59:1244-1249. Nair, V.D., D.A. Graetz, and D.O. Dooley. 2003. Food Agri. Environ. 1:217-223. Wang, H.D., W.G. Harris, K.R. Reddy, and E. G. Flaig. 1995. Ecol. Eng. 5:209-227. Significant at p ≤ 0.01 (††) and p ≤ 0.05 (†) as determined by LSD Conclusions Table 1. Average maximum leachate solution concentrations of manure-amended soils used for control (n=8) Chemical Species K+ Ca2+ P Fe2+ Al3+ SO42- Na+ Cl- NH4+ NO3- mg L-1 375 312 68.0 0.60 0.30 345 144 169 39.0 257 Acknowledgements Repeated water and ammonium chloride extractions and speciation of column leachates confirm that sparingly-soluble phases of P associated with Mg and Ca control P release from the manure-amended soils and maintain elevated P concentrations in soil solutions even years after abandonment of the dairies. Mg-P associations in manure and manure-amended soils could maintain elevated P solubility, and Mg in soil solution could inhibit formation of stable forms of Ca-P. Preemptive dietary controls to maximize Ca-P and minimize Mg-P in manure would be a strategy to reduce P loss from these soils in the future. This research was supported in part by a grant from the USDA-NRI Bill Reeve, Dawn Lucas, Gavin Wilson, Greg Means, Lisa Cowart, Lisa Stanley, Myrlene Chrysostome, Xinde Cao, and Wayne Acree (MAIC) Major Analytical Instrumentation Center for assistance in SEM & EDS analyses