March 2, 2007
Compost Source and Rate Effects on Soil Macronutrient Availability Under Saint Augustine Grass and Bermuda Grass Turf
By Wright, Alan L; Provin, Tony L; Hons, Frank M; Zuberer, David A; White, Richard H
Compost application to turf grasses can increase availability of nutrients in soil and improve growth, but can potentially lead to accumulation of macronutrients in soil and contribute to leaching and runoff losses. The objectives of this study were to investigate the influence of compost source and application rate on concentrations of plant-available macronutrients in soil over 29 months after a one-time application to saint augustine grass [Stenotaphrum secundatum (Walt.) Kuntze] and Bermuda grass [Cynodon dactylon (L.) Pers.] turf. Compost application increased soil organic C, P, Ca, and S concentrations by 3 months after addition, but further increases from 3 to 29 months were seldom observed. In contrast, NO^sub 3^-N and K levels declined while Mg levels increased slightly from 3 to 29 months. Seasonal or cyclical patterns of soil macronutrient levels were apparent, as lower concentrations were observed during dormant stages of Bermuda grass growth in winter. Initial macronutrient concentrations of compost sources strongly influenced macronutrient dynamics in surface soil, while higher application rates resulted in higher levels of P, K, Ca, Mg, but not NO^sub 3^-N and S. Higher levels of macronutrients in Bermuda grass than saint augustine grass turf suggested plant- mediated uptake and assimilation differed between turf grass species. Utilization of turf grass systems for compost application should take into account plant species composition and the related impacts of plant uptake. Macronutrient concentrations were significantly correlated with both total organic C and dissolved organic C (DOC). Formation of organic matter-cation complexes appeared to influence macronutrient dynamics in soil, and may contribute to leaching and runoff losses.
Increasing importance is being placed on the utilization of agricultural land for disposal of composted organic materials. Considerable research has been conducted on the fate of nutrients in compost-amended agricultural soils, but limited information is available on effects of compost on turf grasses and plant-available macronutrients. Utilization of turf grass systems for disposal of composted biosolids can lead to sequestration of nutrients and decrease potential for leaching and runoff losses, as the turf sod and sequestered nutrients are removed periodically (Gross et al. 1990; Victor et al. 2002).
Application of compost and other organic amendments can potentially alter soil organic matter levels and nutrient cycling (Chang et al. 1991; Eghball 2002). Significant increases in soil nutrient levels often occur after compost addition (Gregorich et al. 1998; Chantigny et al. 2002), with short-term increases attributed to the presence of soluble materials (Chantigny et al. 2002). Seasonal variation of soil macronutrient concentrations is also common and related to plant growth stages and uptake, microbial activity, and temperature effects on the decomposition of soil organic matter and compost (Eghball 2002; Vietor et al., 2002). Nutrient values of composted organic materials are considered moderate, but vary widely between compost sources due to differences in waste materials and processing methods (Smith et al. 1998). Application of compost nutrients at rates above plant requirements or soil assimilative capacity may present leaching or runoff hazards (Easton and Petrovic 2004). In fact, compost application tends to increase potential leaching of cations due to complexation with dissolved organic matter (McBride et al. 1999; Kaschl et al. 2002). Effects of organic amendments may improve soil properties for many years after application ceases (Ginting et al. 2003), as only a fraction of the organic material is initially degraded or becomes available to plants and soil microorganisms (Hadas et al. 1996). Thus, information on effects of compost on long-term macronutrient dynamics in turf grass systems is needed.
For the long-term use of composts in turf grass systems to be effective, management options should minimize negative environmental effects, such as nutrient runoff and leaching. The stability or decomposability of composts added to various turf grass species could be assessed by measuring changes in macronutrients over time from turf grasses amended with compost sources of varying quality and macronutrient levels. A multi-year study was initiated to determine the influence of compost source and rate on seasonal dynamics of total organic C and the plant-available macronutrients N, P, K, Ca, Mg, and S.
Materials and Methods
A field study was established at the Texas A&M University Turfgrass Field Laboratory at College Station, Texas in July 2001 on a Boonville fine sandy loam (fine, smectitic, thermic Chromic Vertic Albaqualfs) formerly under pasture. Average annual rainfall is 980 mm and temperature is 20C for this location.
A completely randomized experimental design with three compost sources and an unamended control, two application rates, and two turf grass species was established on field plots (20 m^sup 2^each) replicated four times. Soil was chiseled to a depth of 35 cm and tilled to 15 cm prior to compost application. Composts were applied by thorough tilling into the top 15 cm of soil in July 2001. Unamended and compost-amended plots were then plugged with saint augustine grass [Stenotaphrum secundatum (Walt.) Kuntze] or seeded with common Bermuda grass [Cynodon dactylon (L.) Pers]. The commercially-available compost sources were DilloDirt (City of Austin, Texas), Bryan Compost (City of Bryan, Texas), and Nature's Way (Nature's Way Resources, Conroe, Texas) applied at 80 and 160 Mg ha^sup -1^. These rates were equivalent to 2.5 and 5.0 cm depths of compost. DilloDirt and Bryan Compost are co-composted landscape wastes and municipal biosolids, while Nature's Way consists of composted landscape wastes containing small amounts of manure. Turfgrasses received NH4 NO3 at 72 kg N ha^sup -1^ in 2001 and 49 kg N ha^sup -1^ in 2002, but no N was applied in 2003. Turfgrasses were mowed to maintain a canopy height of 3.5 cm, with clippings being returned to plots. To minimize moisture stress, supplemental irrigation was provided at 12 mm d^sup -1^ for 60 d after planting, followed by 12 mm every 3 d until November 2001. Thereafter, 6 mm of water was applied every 3 d during the growing season upon onset of symptoms of drought stress.
For each sampling event, 15 soil cores (2.5-cm diam.) were taken from each plot to a depth of 15 cm and composited. Samples were taken in July 2001 before compost application, and in Oct. 2001, March, June, and Nov. 2002, and June and Dec. 2003, corresponding to 3, 8, 11, 16, 23, and 29 months after compost application. Soil sampling times in relation to average monthly precipitation and growth stages of turf grasses at this location are presented in Figure 1. Soil was dried at 650C and passed through a 2-mm sieve.
FIGURE 1. Monthly precipitation for the 29 months after compost application in July 2001. General turf grass growth and dormant periods are noted. Soil sampling occurred at 0, 3, 8, 11, 16, 23, and 29 months after compost application.
Soil organic C was measured by dry combustion using an Elementar VarioMax CN analyzer (Elementar Americas, Inc., Mt. Laurel, New Jersey). Nitrate was extracted with 2 M KCI and analyzed by cadmium- reduction (Dorich and Nelson 1984). Plant-available P, K, Ca, Mg, and S were extracted with acidified NH4 OAc-EDTA (Hons et al. 1990) and analyzed by ICP (Spectro Analytical Instruments, Marlborough, Massachusetts). Characterization data for saint augustine grass and Bermuda grass field plots and three compost sources are presented in Table 1.
Differences in soil properties were observed between sites under saint augustine grass and Bermuda grass, so initial background levels prior to compost application (July 2001) were subtracted from levels at later sampling times. Data in figures thus represents changes in macronutrient concentrations after compost application. Different turf grass species were used to demonstrate compost effects for various turf grasses. Data were analyzed using CoStat (CoStat Statistical Software 2003). ANOVA procedures were performed to determine main effects of compost sources, rates, sampling times, and the two turf grass species (P
Characterization and concentrations of extractable macronutrients in compost sources and in soil from turf grass plots prior to compost application.
Results and Discussion
Extractable NO^sub 3^-N was not affected by compost source and application rate, and did not differ between the two turf grass species. However, NO^sub 3^-N rapidly decreased soon after compost application for all treatments, including unamended soil. Nitrate levels averaged 20 mg N kg^sup -1^ prior to compost application, but decreased to 9, 9, 9, 5, 4, and 5 mg N kg at 3, 8, 11, 16, 23, and 29 months after application. Significant decreases in NO^sub \3^-N for both compost-amended and unamended soil by 3 months are indications of NO^sub 3^-N assimilation by turf grass and microbial biomass during decomposition of compost material or leaching losses, suggesting a N limitation in these systems. Moreover, this N limitation likely slowed compost decomposition and macronutrient accumulation in soil. Even though N fertilizers were added to aid in establishment and growth of turf grass, additional N was needed to prevent it from limiting plant growth and compost decomposition.
Total organic C in unamended soil did not increase by 29 months, except for saint augustine grass, which had significantly greater organic C at 11, 23, and 29 months than at 3, 8, and 16 months (Figure 2). Increases in organic C by 23 and 29 months were most likely a result of contributions from root exudates and decomposition by-products of clippings, as these increases occurred for both compost-amended and unamended soil. Averaged between treatments, Bermuda grass (8.3 g kg^sup -1^) showed a significantly greater increase in organic C than saint augustine grass (6.8 g kg^sup -1^). Significant differences between compost sources were minimal for both turf grass species, but higher compost application rates produced significantly higher organic C than preceding lower rates.
Organic C and most macronutrient cations exhibited temporal variability, as concentrations at 16 and 29 months in winter were often lower than at proximal sampling times. Organic C was significantly lower for all compost treatments and unamended soil at 16 than at 11 and 23 months, which suggests that transient declines in soil organic C were not compost related, but likely influenced by reduced growth or dormancy of turf grass during winter (Figure 1). Turfgrass growth is commonly more vigorous from late spring to summer, with a dormant period from late autumn to winter (Taylor and Gray 1999; Redmon 2002). Turfgrasses were mowed to maintain a 3.5- cm height, and the clippings left on the turf may have contributed to soil organic C. Since turf grass production is lower in cooler than warmer months (Taylor and Gray 1999; Redmon 2002), a lower contribution to soil organic matter at least partially explains lower organic C at 16 and 29 months.
FIGURE 2. Changes in soil organic C under Bermuda grass and saint augustine grass turf up to 29 months after application of three compost sources at rates ranging from 0 to 160 Mg ha^sup -1^. Initial concentrations were subtracted from concentrations at each sampling event.
Average increases in extractable P were significantly higher for Bermuda grass (188 mg kg^sup -1^) than saint augustine grass (110 mg kg^sup -1^) as a result of greater P uptake by plugged saint augustine grass than seeded Bermuda grass (Figure 3). Several months may be required for Bermuda grass production to increase to levels approximating those for saint augustine grass. Significant increases in P were also greater for DilloDirt (320 mg kg^sup -1^) than Bryan Compost (99 mg kg^sup -1^) and Nature's Way (28 mg kg^sup -1^). Effects of application rate were especially apparent for P, as successively higher application rates increased P for Bryan Compost and DilloDirt for both turf grass species compared to lower rates. However, application rates of Nature's Way had minimal effect on P. With the exception of high application rates of DilloDirt to both turf grasses (>80 Mg ha^sup -1^), P did not increase beyond levels observed at 3 months. Phosphorus release from compost decomposition likely remained fairly constant after application, or that P mineralization rates from composts were similar to rates of formation of insoluble Ca-P and Mg-P precipitates. Extractable P varied seasonally in a similar fashion to organic C. Changes were attributed to weather patterns and related growth stages of turf grass, as similar decreases in P at 16 and 29 months compared to proximal sampling times occurred for all compost sources and most application rates. Phosphorus was significantly correlated with both organic C and DOC (Table 2).
FIGURE 3. Changes in extractable soil P under Bermuda grass and saint augustine grass turf up to 29 months after application of three compost sources at rates ranging from 0 to 160 Mg ha^sup -1^. Initial concentrations were subtracted from concentrations at each sampling event.
Extractable K increased with successively higher compost application rates for all treatments (Figure 4). Similar to other cations, average K increases were significantly greater under Bermuda grass (57 mg kg^sup -1^) than saint augustine grass (23 mg kg^sup -1^). The average increase in K was highest for DilloDirt (66 mg kg^sup -1^) and lowest for Nature's Way (12 mg kg^sup -1^). In contrast to Ca and Mg, K decreased from 3 to 29 months. This significant decrease in K occurred regardless of compost source and application rate, but did not occur for unamended soil. Significant decreases in K occurred at 16 months for all compost sources and rates compared to proximal sampling times, and to a lesser extent at 29 months. Similar to Ca, K was often below pre-application levels for unamended soil and treatments receiving low application rates. Thus, K may have been assimilated by turf grass to a greater extent than other macronutrient cations, was complexed with organic matter or mineral particles and made unavailable to turf grass, and/or K- bound organic matter was leached from soil. Potassium decreases have been observed in coarse-textured surface soils receiving compost, with enrichment of K in subsurface soils (Harrison et al. 1994). As in our study, Ca and Mg levels were greater in compost-amended than unamended soils (Harrison et al. 1994). Heavy applications of Ca and Mg in organic amendments can also limit K availability (Warman and Termeer 2005), which may explain K dynamics in our study.
Statistically significant (P
FIGURE 4. Changes in extractable soil K under Bermuda grass and saint augustine grass turf up to 29 months after application of three compost sources at rates ranging from O to 160 Mg ha^sup -1^. Initial concentrations were subtracted from concentrations at each sampling event.
FIGURE 5. Changes in extractable soil Ca under Bermuda grass and saint augustine grass turf up to 29 months after application of three compost sources at rates ranging from O to 160 Mg ha^sup -1^. Initial concentrations were subtracted from concentrations at each sampling event.
Average increases in extractable Ca were significantly greater for Bermuda grass (1.7 g kg^sup -1^) than saint augustine grass (0.6 g kg^sup -1^), greater for DilloDirt (3.1 g kg^sup -1^) than Nature's Way (0.3 g kg^sup -1^), and greater for Nature's Way than Bryan Compost (0.05 g kg^sup -1^) (Figure 5). Increasing application rates increased Ca for all sources. For all sources, composts had minimal impacts on Ca beyond the initial increases observed at 3 months. An exception was DilloDirt applied at 160 Mg ha^sup -1^. In fact, initial increases in Ca, and likely other macronutrient cations, at 3 months likely represent contributions from the soluble fractions of compost.
Extractable Mg reacted similarly to Ca, with Bermuda grass having significantly greater average increases (53 mg kg^sup -1^) than saint augustine grass (41 mg kg^sup -1^) (Figure 6). Increases in Mg were also significantly greater for DilloDirt (97 mg kg^sup -1^) than Nature's Way (24 mg kg^sup -1^) and Bryan Compost (22 mg kg^sup -1^). Extractable Mg increased with successively greater application rates for all compost sources under both turf grass species. Magnesium concentrations decreased below initial background levels for unamended soil. Complexation of Mg with organic matter, and leaching of organo-Mg complexes below the soil surface, may explain these results. In addition, application of Naladen irrigation water during summer may enhance leaching losses of soil cations, especially when these cations form associations with DOC. For Bermuda grass, Mg did not increase from 3 to 29 months for any treatment. However, Mg under saint augustine grass increased throughout the study, with the exception of decreases during winter at 16 and 29 months. In contrast to Bermuda grass, Mg in saint augustine grass was significantly greater at 29 than 3 months for unamended soil and Bryan and DilloDirt treatments. Both Ca and Mg exhibited similar significant relationships with organic C, DOC, and P (Table 2).
FIGURE 6. Changes in extractable soil Mg under Bermuda grass and saint augustine grass turf up to 29 months after application of three compost sources at rates ranging from O to 160 Mg ha^sup -1^. Initial concentrations were subtracted from concentrations at each sampling event.
For unamended soil and some treatments under saint augustine grass, extractable Ca, Mg, and K decreased to levels below those observed prior to compost application. These results may be an indication of chelation with soil organic matter or dissolved organic matter, which may decrease cation availability to plants and the potential to be extracted with the methods used in this study. Indeed, cation mobility in high pH sandy soils was enhanced by association with dissolved organic matter (Guggenberger et al. 1994; McBride et al. 1999). Greater organic matter solubility at high pH promotes reaction with cations and retards the formation of insoluble metal oxides and hydroxides (Spark et al. 1997). In the relatively high pH sandy soil in this study (pH 7.4), formation of organo-mineral complexes may decrease availability of extractable cations. These reactions may explain the general failure of compost to increase concentrations of macronutrient cations over time and decreases in K over the same time period. Furthermore, the mobility of dissolved organic matter-bound \cations may be enhanced through preferential flow paths caused by improved aggregation and soil structure initiated by additions of large quantities of compost and organic materials (Gounaris et al. 1993; Camobreco et al. 1996; Debosz et al. 2002). This would further increase the potential leaching of organic matter-associated cations in soil.
Extractable S reacted differently than other macronutrients in response to compost application (Figure 7). In contrast to Ca, Mg, K, and P, compost application rate had little effect on average extractable S except for DilloDirt treatments. However, similar to other macronutrients, the increases of extractable S were significantly greater under Bermuda grass (21 mg kg^sup -1^) than saint augustine grass (13 mg kg^sup -1^), and greater for DilloDirt (32 mg kg^sup -1^) than other compost sources. Sulfur exhibited considerable seasonal variability, including a decrease at 8 months compared to 3 and 11 months that did not occur for other macronutrients. In addition, S decreased at 16 months similar to all other macronutrients, but did not decline at 29 months. Overall, S increased over time for unamended soil and treatments receiving compost, suggesting that increases were not compost related but due to impacts of turf grass on nutrient cycling and organic matter decomposition. Extractable S was significantly related to both soil organic C and DOC, along with other macronutrients except NO^sub 3^- N (Table 2).
FIGURE 7. Changes in extractable soil S under Bermuda grass and saint augustine grass turf up to 29 months after application of three compost sources at rates ranging from O to 160 Mg ha^sup -1^. Initial concentrations were subtracted from concentrations at each sampling event.
Compost sources, due to differences in macronutrient concentrations, had varying effects on soil macronutrient concentrations from 3 to 29 months. DilloDirt, which had the highest initial background macronutrient levels (Table 1), produced the highest levels in soil. Even trends in macronutrient concentrations over time were similar for all sources. Thus, sources only affected the magnitude of responses to added composts. The response of soil macronutrients to compost application rates showed similar trends as the response to sources. Thus, a greater macronutrient loading to soil, either caused by higher application rate or higher concentrations in composts, increased macronutrient levels in soil. Soil under saint augustine grass had higher levels of organic C and most macronutrients prior to compost application. Differences in background macronutrient levels in soils prior to compost application were negated by normalization of data for expression of increases or decreases in macronutrients over time. Increases in P, K, Ca, Mg, and S were significantly greater under Bermuda grass than saint augustine grass. Thus, plant species had a significant impact on macronutrient dynamics in compost-amended soil. Reasons for differences in the response of turf grass species to compost application need to be investigated.
Compost application initially increased soil organic C, and extractable P, Ca, and S, but continued increases were not observed in the period of 3 to 29 months after application. Extractable NO3- N and K, in contrast to other macronutrients, declined from 3 to 29 months, while Mg increased up to 29 months after application to saint augustine grass. Initial macronutrient concentrations of compost sources strongly influenced macronutrient levels in soil, while increasing compost application rates resulted in higher levels of extractable P, K, Ca, and Mg but not NO3-N and S. Macronutrient concentrations in compost-amended soil were dependent on turf grass species, as greater increases in macronutrients were observed under Bermuda grass than saint augustine grass. Complexation of macronutrient cations with dissolved organic matter, especially in sandy soils, likely contributed to the general failure of composts to significantly increase concentrations of macronutrients over time.
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Alan L. Wright1, Tony L. Provin2, Frank M. Hons2, David A. Zuberer2 and Richard H. White2
1. Everglades Research & Education Center, University of Florida, Belle Glade, Florida
2. Department of Soil and Crop Sciences, Texas A&M University, College Station, Texas
Copyright J.G. Press Inc. Winter 2007
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