Municipal programs promoting composted municipal biosolids (CMB) as soil amendments for turfgrass establishment recommend large volume-based application rates. Turfgrass establishment practices were compared to evaluate impacts of volume-based rates of contrasting CMB sources on runoff water quality. Sod transplanted from Tifway bermudagrass [Cynodon dactylon (L.) Pers. x C. transvaalensis Burtt-Davy, var. Tifway] turf topdressed with a 1.2-cm depth of two CMB sources was compared to Tifway sprigged in soil mixed with 12.5% and 25% by volume of each CMB during eight natural rain events. The two CMB comprised High (9500 mg P/kg) and Low (5800 mg P/kg) concentrations of total P. Sod grown with High-P and Low-P CMB, sprigged plots amended with the two rates of High-P and Low-P CMB, and an established bermudagrass control made up seven treatments that were replicated three times on an 8.5% slope. Runoff was sampled after each of eight natural rain events and soil was sampled to a 5-cm depth after the eighth event. Topdressing or incorporation of a 1.2-cm depth of CMB supplied 280 kg/ha of total P from Low-P CMB and 599 kg/ha of total P from High-P CMB. Although import of CMB in transplanted sod limited sediment loss, sod transplanted from turf top-dressed with the 1.2-cm depth of High-P CMB contributed to greater soil and runoff concentrations and mass loss of total N and P than the same depth incorporated to a 5-cm soil depth before sprigging. Incorporation of CMB in soil minimized differences in mass loss of total N and P in solution and sediment among volume-based CMB rates applied to sprigged treatments and the control. Regression analysis indicated concentrations of extractable P in soil amended with CMB were directly and positively related to concentration and mass loss of dissolved P in runoff.
Many municipalities and associated industries produce and market composted municipal biosolids (CMBs) as soil amendments for vegetation establishment, including turfgrass, on commercial and residential landscapes (City of Austin, 2001; Dickerson, 1999; Milwaukee Municipal Sewerage District, 2004). Recycling CMB across urban landscapes diverts waste streams from landfills and facilitates nutrient and carbon cycling. Historically, the use of CMB in turfgrass management systems focused on plant responses to amended soils (Schlossberg and Miller, 2004; Loschinkohl and Boehm, 2001; O’Brien and Barker, 1995; Flanagan et al., 1993). The CMB amendments decreased incidence of disease, enhanced color, reduced establishment time, and delayed water stress of turfgrass established on disturbed urban soils and sod production fields (Boulter et al., 2002; Loschinkohl and Boehm, 2001; Garling and Boehm, 2001; Smith, 1996; Murray et al., 1980).
Depth- and volume-based CMB application rates are promoted through municipal programs. For example, the City of Austin, Texas recommends incorporation of 25% by volume of CMB into a 15-cm depth of soil or topdressing of a 0.6-cm depth of CMB (City of Austin, 2001). Similarly, evaluations of CMB amendments for turfgrass have included large, volume-based CMB rates to enhance soil physical properties during establishment on poor quality soils (Landschoot, 1995; Cisar, 1994, Angle, 1994). Yet, little information concerning nutrient losses in surface runoff from soils amended with the large volume-based CMB rates is available.
Line et al. (2002) identified compost and mulches among factors that contributed to nutrient loss in runoff water from urban construction sites. Nutrient losses in runoff water from amended soil and turf are expected to increase as nutrient concentrations in soil increase, whether applied as inorganic or organic fertilizer sources (Easton and Petrovic, 2004; Vietor et al., 2004; Gaudreau et al., 2002). The nutrient loads in urban runoff are considered a major source of non-point surface water pollution (Carpenter et al., 1998).
Large, volume-based applications of CMB to soil need to be evaluated to quantify nonpoint-source nutrient losses in surface runoff from urban landscapes. In addition, the traditional approach of mixing CMB with urban soils prior to sprigging or seeding of turfgrass needs to be compared to the practice of importing CMB in sod transplanted for turfgrass fields grown with CMB (Vietor et al., 2004). A previous study indicated transplanted sod delayed runoff of simulated rain more than wood or fiber blankets applied to 8% or larger slopes on simulated construction sites (Krenitsky et al., 1998). A comparison of runoff losses from CMB-amended soil and CMB-amended sod will contribute to optimal practices for minimizing sediment and nutrient losses during vegetation establishment and soil stabilization at urban construction sites.
The objectives of this study were: (i) quantify and compare export of total and extractable P and N in sod harvests among turfgrass sources produced with inorganic fertilizer and two sources and rates of composted municipal biosolids (CMB), (ii) quantify and compare P and N runoff losses between sod transplanted from CMB-produced turfgrass and turfgrass sprigged in CMB amended soil, and (iii) relate runoff concentrations and mass losses of P to extractable soil P concentrations of turf establishment treatments.
Turfgrass Sod Production
Sod production treatments were imposed under irrigated conditions at the Texas A&M University (TAMU) Turfgrass Field Laboratory, College Station, TX between May and August 2004. Six treatments were replicated four times in a randomized complete block design. Individual plots measured 3.0 m by 4.5 m. Treatments differed with respect to P source and rate. Treatments comprised a control (0 kg P/ha), inorganic P fertilizer (50 kg P/ha), and two CMB sources topdressed at 12.5% and 25% by volume (v/v) of a 5-cm depth of soil. The two CMB sources were available for purchase from the cities of Austin and Bryan, Texas. The total P (TP) concentration on a wet weight basis in the Austin source (7.8 g/kg) was two times greater than that of the Bryan source (3.6 g/kg). The Austin source was designated as High-P and the Bryan source as Low-P CMB. The two CMB rates represented 50 and 100% of the volume-based rates recommended for urban soils in Austin, Texas. The CMB was topdressed after sprigging Tifway bermudagrass [Cynodon dactylon (L.) Pers. x C. transvaalensis Burtt-Davy, var. Tifway] in a 5-cm depth of imported loamy sand. The loamy sand was applied over an exposed Eg horizon of a truncated Boonville fine sandy loam soil (fine smectitic thermic Chromic Vertic Albaqualf). Total and extractable P and N concentrations in the 5-cm layer of loamy sand and in CMB sources were analyzed prior to treatment applications. Inorganic N fertilizer was applied as ammonium sulfate (NH4)2SO4 to all plots at rate of 50 kg N/ha on 15, 24 June; 2, 13, 23 July; and 16 August 2004 to promote rapid turf establishment.
Turf was mowed to 3 cm when grass height reached 8 cm. Turfgrass sod was harvested to a 2.5-cm depth on 26 August 2004. Four 10-cm diameter plugs were sampled from each plot. The plugs were used to estimate total P and N amounts in soil and plant components and extractable P and N in the soil component of the harvested sod layer. Plant and soil components of sod were separated in an acidified (pH = 4) wash solution to reduce N loss. The wash solution was combined with soil and dried at 60 C. Dried soil and plant components were weighed, ground, sub-sampled, and analyzed.
Runoff Water Quality
Experimental Design and Sampling
Runoff water quality was compared between transplanted sod and CMB-amended soil on an 8.5% slope excavated from the Boonville soil at the TAMU Turfgrass Field Laboratory. A randomized complete block design comprised three replications of seven treatments that were installed on 1.5 m by 4-m plots (Gaudreau et al., 2002; Vietor et al., 2004). A 10-cm width of sheet metal was inserted to a 2.5-cm depth around plot perimeters to isolate and channel runoff through individual H-flumes into uncovered 311-L tanks. Except for an established bermudagrass (Cynodon dactylon L.) control, plot surfaces were excavated to a 5-cm depth to simulate a disturbed urban landscape before treatments were imposed. Three treatments consisted of the bermudagrass control and sod transplanted from turf top-dressed with a 1.2-cm depth of High-P or Low-P CMB. Four additional treatments comprised Tifway sprigged into a 5-cm depth of sandy-clay loam soil (fine, mixed, thermic Fluventic Ustochrept) mixed with 12.5% or 25% by volume of the High-P or Low-P CMB source.
Total Kjeldahl N (TKN), nitrate-N (Nit-N), total P (TP), Mehlich-3-extractable P (STP), and water extractable P (WEP) of amended soil and transplanted sod were measured at the start and end of the runoff sampling period. Runoff volumes of eight rainfall events were measured and sampled from 28 August 2004 through 1 April 2005. Runoff was sampled immediately after rain events or before collection tanks overflowed. The samples were stored in a refrigerator at 4°C or placed on ice prior to centrifuging a 100-mL sub-sample. Centrifuging and filtering were initiated within 24-h of runoff, except for the first rain event on 28 August 2004. Samples from the first event were refrigerated for 36-h at 4 C prior to centrifuging. The sub-samples were centrifuged at 3600 rpm for 30 minutes. The supernatant was decanted and filtered for analysis of total dissolved P (TDP) and dissolved reactive P (DRP). Subsamples of filtrate were submitted to the Texas Cooperative Extension Soil, Water, and Forage Testing Laboratory for analysis of TKN, Nit-N, and TDP. The sediment recovered during centrifuging and filtering was dried, weighed, and ground for analysis and computations of TP and TKN.
Three plugs (10-cm diameter and 5-cm deep) were sampled from plots after the final runoff event to compare turfgrass root and shoot biomass among treatments. The plugs were washed in an acidified solution (pH = 4) to separate plant tissue from soil and CMB residues.
Turfgrass, CMB, sediment, and soil samples were digested according to a modified Kjeldahl method (Parkinson and Allen, 1975). The TKN concentration in digests was measured colorimetrically (Dorich and Nelson, 1983). The Mehlich 3 method was used to extract plant-available P from compost sources and soil (Mehlich, A. 1984). The Nit-N in compost and amended soil was extracted as described by Keeney and Nelson (1982). In addition, Nit-N and P in CMB and soil were extracted in distilled water to quantify nutrients susceptible to loss through leaching and runoff. One g soil was extracted in 10 mL distilled water for 1 hr on an orbital shaker. An auto-analyzer was used to quantify Nit-N in extracts through cadmium reduction (Dorich and Nelson, 1984). Concentrations of TP in digests and TDP in extracts of soil and filtrate of runoff were analyzed through inductively coupled plasma optical emission spectroscopy (ICP). The DRP in water samples and extracts of CMB and soil was determined colorometrically within 24 h of filtering (D’Angelo et al., 2001).
Analysis of variance (ANOVA) (SAS version 9.0) and mean separations among treatments were conducted for sod production and runoff experiments (SAS Institute Inc, 2000). In addition, ANOVA among treatments was completed for individual runoff events if interactions between treatments and sampling dates were significant (P=0.05). Regression analysis was used to evaluate the relationship of mean concentration and mass loss of TDP in runoff to STP and WEP concentrations in soil during eight rain events. A T-test was performed to evaluate differences in slopes of the regression relationships between the two CMB sources (Kleinbaum and Kupper, 1978).
Turfgrass Sod Production
The turfgrass sod was harvested on 26 August 2004, four months after bermudagrass sprigs were planted. Although Nit-N was applied in CMB and five fertilizer applications totaling 300 kg/N, mean Nit-N concentrations in the harvested sod layer were low. The Nit-N concentrations on a wet basis in High-P CMB were 34% greater than Low-P CMB, but Nit-N concentrations in soil of the sod layer did not differ among treatments at harvest.
Low and similar Nit-N concentrations within and below the harvested sod layer for the control and CMB-amended treatments indicated turf plants used a major portion of applied Nit-N during turf establishment. In contrast to the low soil Nit-N concentrations, top-dressing of two sources and rates of CMB increased (P = 0.05) soil TKN concentration within the harvested sod layer compared to treatments receiving only inorganic N and P fertilizers. Doubling the volume-based rates of respective CMB sources increased (P = 0.05) soil TKN concentrations. Yet, TKN concentration in soil beneath the sod layer was similar between CMB-amended treatments and the control.
Amending sod production plots with CMB, even at 12.5% by volume, increased soil test P (STP) to concentrations 5 times greater than recommended agronomic levels. In addition, top-dressing of the two CMB sources at each rate increased (P = 0.05) STP of the harvested sod layer compared to the control and sod top-dressed with 50 kg ha-1 of fertilizer P. Moreover, increasing the rate of either CMB source from 12.5% to 25% by volume increased (P=0.05) the STP concentrations in the sod layer. For each CMB rate, STP was greater (P = 0.05) in the sod layer amended with High-P than with Low-P CMB. Similar STP concentrations between the control and CMB-amended treatments within the 5-cm depth of soil below the sod layer indicated STP applied in CMB was exported with the sod harvest.
Similar to changes in STP, the 25% by volume rates of both CMB sources and the 12.5% rate of the High-P CMB increased TP in the sod layer compared to the control and fertilizer-grown sod. Although CMB topdressings increased TP within the sod layer, the single sod harvest effectively removed the TP applied in CMB. The TP concentrations within the 5-cm depth of soil below the sod layer were similar to the control. In previous studies of manure export through sod, up to 77% of TP in topdressings of composted manure was exported through a single sod harvest of Reveille bluegrass (Poa arachnifera Torr. X P. pratensis L.) (Vietor et al., 2002).
The dry weight of Tifway bermudagrass biomass (Mg/ha) in the sod layer was similar (P = 0.05) among treatments and ranged from 10 to 14 Mg/ha (dry wt). Topdressing CMB at volume-based rates (12.5% and 25% of the surface 5-cm) over establishing sprigs did not limit bermudagrass growth compared to applications of inorganic fertilizer only. Similar biomass yield between the control, which received inorganic N fertilizer only, and other treatments indicated soil P concentrations in control plots were not limiting.
Runoff Water Quality
Soil and Runoff Depth
Increases of soil nutrient concentrations above that of annual crop requirements can contribute to loss of dissolved and sediment-bound nutrients in runoff water (Carpenter et al., 1998). Contrasting establishment treatments in the present study contributed to increased concentrations and potential runoff loss of soil nutrients. The soil Nit-N and TKN concentrations in sod transplanted from turf top-dressed with CMB were greater (P = 0.05) than sprigged treatments in which soil was mixed with the two rates of Low-P CMB. For each CMB source, top-dressing and import with transplanted sod increased (P = 0.05) soil TKN concentration compared to equal and lesser rates that were incorporated within the 5-cm soil depth of sprigged treatments. In addition to diluting concentrations of applied Nit-N or TKN near the soil surface, incorporation of CMB could reduce potential transport and loss in surface runoff.
Concentrations of extractable P forms in the 5-cm depth were similarly greater (P = 0.05) for transplanted sod than sprigged treatments in which CMB was incorporated. Concentrations of WEP, a potential indicator of P loss through leaching or runoff, were greater for sod containing top-dressed CMB than for soil mixed with the respective CMB (Sharpley and Moyer, 2000). In addition, doubling the volume based CMB rate mixed with soil increased WEP for the respective CMB. Variation of STP among treatments was similar to WEP, except the 12.5% rate of Low-P CMB was not different from the 25% rate or control. In contrast to Nit-N, STP concentrations exceeded agronomic P levels (50 mg/kg) for all treatments amended with CMB.
Variation of runoff depth and concentration and mass loss of N and P forms and sediment was analyzed separately for each runoff event to accommodate a significant (P = 0.05) interaction between treatments and runoff events. Rainfall depths varied between 12 and 49 mm and totaled 210 mm during the eight events. Yet, runoff depth varied among treatments on the first event only, 2 d after treatments were imposed. Runoff depth was 2 times greater (P = 0.05) for transplanted sod than for the established bermudagrass control and turf sprigged into soil mixed with the 12.5% rate of High-P CMB on the first date. Runoff depth did not differ among the two sources and rates of CMB incorporated in sprigged treatments. The magnitude of treatment differences in runoff depths diminished as Tifway bermudagrass established on the sprigged treatments. The portion of rainfall recovered in runoff declined from 67% to 25% from the first to last runoff event.
Concentrations in Runoff
Concentrations of TDP in runoff water differed (P = 0.05) among treatments during each of eight rain events. During the first two rain events, TDP concentrations in runoff from transplanted sod were greater (P = 0.05) than the control and sprigged treatments amended with CMB (Table 5). In addition, TDP concentration in runoff was greater (P = 0.05) for sod amended with Low-P CMB than for High-P CMB. The difference in runoff concentration of TDP between the two sod sources for the first two events occurred despite similar WEP concentrations within the 5-cm depth of these two treatments.
During five subsequent runoff events, comparative soil WEP concentrations were reflected in similar TDP concentrations in runoff between the two sod sources. In addition, greater TDP concentrations in runoff from transplanted sod than from the control and sprigged treatments amended with CMB were consistent with soil WEP differences between treatments. Moreover, greater STP concentrations in the sampled layer of transplanted sod than for sprigged plots for a respective CMB is consistent with greater TDP concentration in runoff from transplanted sod. The results indicate CMB incorporation in soil can reduce the quantity of P dissolved and transported in runoff water (Daverede et al., 2004; Pote et al., 2003; Sharpley 1985). In addition, CMB products high in TP could be incorporated at volume-based rates recommended for urban soils without increasing TDP concentration in runoff compared to established bermudagrass supplied inorganic nutrients (Tarkalson and Mikkelsen, 2004). Moreover, variation of TDP concentration in runoff among all treatments was small on a sampling date seven months after treatments were imposed.
Variation of filtrate concentrations of TKN among establishment treatments was indicative of variation of mass loss of TKN in runoff. Although an interaction between treatment and rainfall event was significant (P = 0.05), the ranking of mean TKN concentrations in runoff among treatments was similar over rain events. During four runoff events after treatments were applied, mean TKN concentration in runoff was greater (P = 0.05) for sod transplanted from turf grown with High-P CMB (11.2 mg/L) than for turf grown with low-P CMB (8.8 mg/L). During five runoff events, mean TKN concentration in runoff from sod grown with High-P (12.2 mg/L) and Low-P CMB (10.0 g/L) were greater (P = 0.05) than the control and soil mixed with either CMB source (5.5 mg/L) before sprigging. The ranking of runoff concentration of TKN among treatments over the first six runoff events reflected similar treatment differences in soil TKN concentration.
Low Nit-N concentrations in runoff were consistent with low soil test concentrations of Nit-N among establishment treatments. The Nit-N concentrations were generally less than 1.0 mg/L for all treatments during each rain event. The Nit-N concentration in runoff water differed among treatments on only two of eight runoff event. Easton and Petrovic (2004) reported runoff concentrations up to 10 mg/L in runoff from a 7 to 9% slope after application of natural organic N (100 kg/ha) sources, including biosolids, during early turf establishment. Yet, their organic N sources were top-dressed on newly seeded cool-season perennial grass rather than incorporated in soil or imported with sod.
Mass Losses in Runoff
Variation of magnitude of treatment differences in mass loss of TDP contributed to an interaction between treatment and event, but the mean rank among treatments was consistent among events. The mean mass loss of TDP in runoff from transplanted sod was less (P = 0.05) for the Low-P CMB (96 mg/sq. m) than the High-P CMB (153 mg/sq. m) sod source during only two of eight rain events. In addition, mean TDP mass loss (mg/sq. m) in runoff was consistently greater for sod grown with High-P (106 mg/sq. m) or Low-P CMB (76 mg/sq. m) than from the control and sprigged treatments amended with volume-based CMB rates (26 mg/ sq. m). Similar treatment differences were observed for mass loss of TDP summed over eight runoff events. Consistent with results of Tarkalson and Mikkelsen (2004), variation of total mass loss of TDP among treatments indicated incorporation of either CMB source effectively limited TDP mass loss compared to CMB imported with transplanted sod. Vietor et al. (2004) reported greater TDP losses in runoff water when composted dairy manure was applied to sprigged bermudagrass rather than imported with transplanted sod. In contrast to the present study, the composted dairy manure was top-dressed on sprigged treatments rather than incorporated.
A major portion of TDP mass loss was in the DRP fraction for all treatments. The DRP mass loss (mg/sq. m) was greatest over eight rain events for transplanted sod. Yet, the fraction of TDP mass loss in DRP was 50% lower in runoff from the transplanted sod than from CMB mixed in the 0 to 5-cm soil layer. The DRP mass loss in runoff from sprigged treatments ranged between 57 and 77% of the TDP mass loss over eight runoff events. Previous observations of DRP loss in runoff indicated surface applications of manure, rather than soil, were the primary sources of runoff P, which determined the percentage of DRP in TP losses (Kleinman et al., 2002). Conversely, DRP loss from manure mixed with soil was similar to unamended soil and related to soil P concentration and desorption of P from soil.
Sediment loss in runoff varied among treatments during the first and second runoff events after treatments were imposed and on Nov 1. Totaled over eight runoff events, sediment loss was less (P = 0.05) for transplanted sod than for three sprigged treatments in which CMB was mixed with soil. The total mass of sediment was 2 to 3 times greater for sprigged compared to transplanted sod treatments. Previous observations of runoff loss under simulated rain indicated runoff loss of suspended solids from soil mixed with manure was 200% greater than from top-dressed manure (Kleinman et al., 2002).
Mean mass losses of TP and TKN in sediment were not different among treatments over the first six rain events. Yet, cumulative mass losses of TP and TKN in the sediment fraction were greater for sod transplanted from turf grown with High-P CMB than the other sod source or sprigged treatments amended with either CMB source. Analyses of soil sampled from the 0- to 5-cm depth indicated greater TP and STP concentrations in sod grown with High-P CMB contributed to greater mass loss of TP in sediment from High-P sod than from other treatments. Mass loss of TP in sediment and mean STP in sod grown with High-P CMB were more than 70% greater than the next lower mean of each variable for other establishment treatments. Similarly, mass loss of TKN in sediment was 118% greater and soil TKN concentration was 52% greater for sod grown with High-P CMB than for the second ranking treatment. Incorporation of both CMB sources in soil limited mass loss of TKN and TP in the sediment fraction of runoff to amounts similar to the established bermudagrass control.
The sums of mass losses of TP and TKN in sediment over eight runoff events were similar in magnitude to mass losses of TDP and TKN in runoff water for sprigged treatments in which CMB was incorporated. In contrast, import of Low-P CMB in transplanted sod reduced sediment-bound losses to 49% of dissolved TKN and to 22% of TDP. Yet, the high TKN and TP concentrations in sod imported from turf grown with High-P CMB diminished differences between mass losses of sediment-bound and dissolved N and P forms. Mass loss of TKN in sediment was 76% of dissolved TKN in runoff from sod grown with High-P CMB. Similarly, TP in sediment was 56% of TDP in runoff water.
Similar to variation of concentrations, Nit-N mass losses were low compared to TKN and differed among treatments during only three runoff events. The sum of mass losses over eight runoff events indicated Nit-N mass loss from transplanted sod and sprigged treatments amended with High-P CMB were greater than the established bermudagrass control. Yet, variation of mass loss of Nit-N was not related to variation of soil-test or runoff concentrations of Nit-N among treatments.
Relationship Between Soil and Runoff Losses
Mean concentration and mass loss of TDP in runoff were regressed against WEP and STP for each treatment replication. Previous evaluations have questioned the utility of STP alone for managing the risk of direct P loss in runoff from fertilizers and organic wastes applied to soil (Sims et al., 2000). Eghball et al. (2002) reported runoff losses of dissolved P forms were not well correlated to STP concentrations just after organic nutrient sources are applied. In contrast, Vietor et al. (2002) reported a positive, direct relationship between mean TDP loss in runoff water and STP for sod transplanted from turfgrass top-dressed with P-based rates of composted dairy manure. A similar study of P transfer in runoff after application of biosolids and fertilizer indicated P release was related to amounts extracted in water (Withers et al., 2001).
Variation of mean TDP concentration in runoff for eight runoff events sampled during the present study was positively and directly related to variation of both soil WEP and STP concentrations among CMB-amended treatments. Yet, variation of slopes of regression relationships between extractable P forms and TDP in runoff between compost sources revealed limitations of WEP and STP as environmental indicators. The predicted mass loss of TDP in runoff was less for treatments amended with Low-P than High-P CMB as soil WEP concentration increased above 12 mg/kg. Conversely, predicted TDP concentration in runoff was less for High-P than Low-P CMB as STP concentration increased above 500 mg/kg. Yet, relationships between soil WEP and TDP concentration and between STP and TDP mass loss in runoff were similar between Low-P and High-P CMB. Variation of the relationships between extractable soil P forms and TDP concentrations and runoff mass losses reveal both the utility and limitations of extractable soil P tests alone for evaluations of the potential impacts of agricultural practice on water quality.
Tifway bermudagrass biomass (Mg/ha) comprised the above ground portion and roots harvested from the 0 to 5-cm soil layer of treatments. The biomass yield was calculated approximately 3 mo after treatments were imposed on the runoff plots. Biomass was consistently greater (P = 0.05) for transplanted sod than for sprigged treatments. Biomass dry weight after the last runoff event was 17 Mg/ha for sod transplanted from turf grown with Low-P CMB and 13 Mg ha-1 for sod grown with High-P CMB. The biomass yield after incorporating CMB into the soil at the 12.5% volume based rate was 6 and 8 Mg ha-1 for the Low-P and High-P CMB, respectively. Similarly, the biomass yield after incorporating CMB at the 25% volume based rate was 6 Mg ha-1 for the Low-P CMB and 7 Mg ha-1 High-P CMB. Further study is needed to quantify the potential contribution of clippings to the fate and transport of nutrients after transplanting of sod or sprigs.
Educational & Outreach Activities
Hansen, N.E., D.M. Vietor, R.H. White, T.L. Provin, and C.L. Munster. 2005. Turfgrass Sod Production as a System for Cycling Composted Municipal Biosolids Across Urban and Agricultural Landscapes. Abstracts of Annual Meeting of Southern Branch of American Society of Agronomy. San Antonio, TX.
Variation associated with nutrient concentration of CMB and different rates and methods of CMB application affected nutrient export through bermudagrass sod harvests and sod impacts on water quality. Topdressing of volume-based rates of contrasting CMB sources enabled complete removal of applied N and P forms in a single sod harvest. Yet, sod transplanted from turf top-dressed with volume-based CMB rates contributed to greater soil and runoff concentrations and mass loss of N and P forms than volume-based CMB rates incorporated in soil. Although import of CMB in transplanted sod reduced sediment loss compared to CMB-amended soil sprigged with bermudagrass, imports of CMB in sod contributed to runoff loss through dissolved and sediment fractions. The high concentrations of TKN, TP, STP, and WEP in sod amended with High-P CMB were consistently associated with greater mass loss of the respective nutrients in runoff compared to CMB-amended soil in sprigged treatments. Conversely, incorporation of CMB in soil minimized variation of mass loss of TP and TKN in solution and sediment among sprigged treatments and the control even though CMB increased soil concentrations of P and N. Yet, regression analysis indicated concentrations of STP and WEP in transplanted sod or soil amended with CMB was directly and positively related to concentration and mass loss of TDP in runoff. Variation of the regression relationships indicated soil concentrations alone were not sufficient predictors of CMB impacts on water quality.
Hauling costs are a major budget component and determinant of the economic feasibility of cycling and exporting composted municipal biosolids (CB) through turfgrass sod. Low nutrient concentrations in CB and objectives for improving soil physical and chemical properties contribute to recommendations for large, volume-based CB rates in support of turfgrass establishment and production. Hauling costs greater than $0.11 /cu. yd./mile provide incentives for locating sod production fields on agricultural land near cities and CB sources. In addition, proximity between sod production sites and urban landscapes on which sod is transplanted minimizes hauling costs for sod. For example, more than one half of the sod applied to landscapes within the Dallas-Ft. Worth Metroplex is hauled from production fields as distant as Oklahoma and the Gulf Coast of Texas. At a hauling cost of $0.005/sq. yd./mile, short hauling distances can offer a competitive advantage for access to sod markets and offset costs of CB purchase and transport for sod production. Yet, high land values for agricultural land near cities can contribute to high capital costs, including prorated purchase costs and interest, if land is purchased to begin a sod enterprise. For a sod producer on the northern fringe of the Dallas-Ft. Worth Metroplex, capital costs for land made up 40% of the of annual sod production costs.
At wholesale prices of $0.85/sq. yd., income from sod sales is approximately $3500/ac. At present, opportunities for increasing or adding value to wholesale prices of sod amended with CB have not been evaluated. The challenge of cycling CB through sod at current prices will be to minimize hauling costs for both CB and the sod product without incurring prohibitive capital costs for agricultural land near cities.
A system for cycling and exporting nutrients and organic matter in wastewater and animal biosolids is currently being operated on agricultural land near the the Dallas-Ft. Worth Metroplex. High value Zoysiagrass is being produced on land purchased to maintain green space between a feedyard and encroaching residential developments.
Areas needing additional study
Variation of the composition and quality of composted municipal biosolids within and among locations necessitates a comprehensive program for characterizing, managing, and marketing compost for turfgrass sod production. After compost physical and chemical properties are known, research is needed to develop recommendations for management of compost rates, fertilizer N, clipping, water, and harvest and transplanting to achieve rapid sod growth while limiting negative environmental impacts. Sod strength and storage life after harvest and water capture and use after transplanting address need to be studied to address pragmatic concerns about turfgrass surfaces in subhumid and semiarid environments. In addition, the fate and transport of water, nutrients, carbon, pesticides, and bacteria need to be evaluated during production and after transplanting of compost-amended sod to compare and balance environmental benefits and costs.