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© 2006 Plant Management Network.
Accepted for publication 21 November 2005. Published 13 January 2006.

Effects of Compost Topdressing on Turf Quality and Growth of Kentucky Bluegrass

G. A. Johnson, former Graduate Student, and Y. L. Qian, Associate Professor, Department of Horticulture and Landscape Architecture, and J. G. Davis, Professor, Department of Soil and Crop Sciences, Colorado State University, Fort Collins 80523-1173

Corresponding author: Y. L. Qian. Yaling.Qian@colostate.edu

Johnson, G. A., Qian, Y. L., and Davis, J. G. 2006. Effects of compost topdressing on turf quality and growth of Kentucky bluegrass. Online. Applied Turfgrass Science doi:10.1094/ATS-2006-0113-01-RS.

Abstract

Long-term over-application of manure to agricultural fields has increased nitrate and phosphorus contamination of groundwater and surface water along the South Platte River basin. Concerns about water quality issues have contributed to the increasing interest in composting manure and topdressing it on turfgrass. The objectives of this research were to evaluate the effects that topdressing manure compost has on: (i) turfgrass quality, (ii) turfgrass growth rates, and (iii) root mass and distribution. Compost treatments at rates ranging from 0 to 99 m³/ha were topdressed onto two cultivars (‘Nuglade’ and ‘Livingston’) of Kentucky bluegrass (Poa pratensis L.) in May and September 2003 and May 2004. A synthetic fertilizer (Urea 46-0-0) was applied to balance inorganic nitrogen rates among treatments. Topdressing compost at 66 and 99 m³/ha increased the overall quality by 10% of both cultivars during the growing season, and allowed the turfgrass to retain color in the fall and early winter and green up faster in the spring. During July and August, the 66- and 99-m³/ha compost treated plots had 48 and 56% higher clipping yield than the control, respectively. No differences in rooting mass among treatments were detected in the 0- to 50-cm depth. These results suggest that compost can improve turf quality and shoot growth via its action as a slow-release fertilizer.

Introduction

Livestock production in the South Platte Basin in Colorado is known to have resulted in nitrate contamination of groundwater and elevated phosphorus levels in reservoirs (22). The environmental problems associated with livestock feedlots and long-term over-application of manure to agriculture fields has promoted livestock producers to compost manure and to search for alternative beneficial use of manure and composted manure.

Composting manure is a useful method of producing a stabilized product that can be stored or spread with little odor or fly breeding potential (21). During the composting process, the C and N present in the manure are converted into more stable organic and humified forms. Composting cattle manure has been shown to have a number of agronomic benefits, including a reduction in material mass and water content, pathogen suppression, decreased weed seed viability, and the production of a stabilized organic material that is easier to handle and spread (5,7,16). The N content of compost is generally lower than that of raw manure and much of the N in composted manure exists in stable organic forms. Therefore, N losses during storage and during and after field application of compost are minimized (4,17).

Until the 1930s, organic amendments (such as manure) served as one of the principal sources of fertilizer for managed turfgrasses (10,18,23). However, the use of compost and manure on turfgrasses declined sharply with the creation of synthetic, urea-based fertilizers that offered more consistent and predictable nutrient-release characteristics and is cheaper to transport (9). Recently there has been renewed interest in utilizing compost on turf because of concerns over the increased use of synthetic fertilizers in the environment, the generation of increased amounts of animal waste and bio-solids, especially in urban/rural interfaces, and efforts to find marketable values for the wastes.

Much research has evaluated the effects of using composted manure as a soil amendment for turfgrass establishment and sod production (1,3,11,12,13). However, much less published research is available regarding the effects of using composted manure as a topdressing material. Garling and Boehm (10) found that topdressing biosolid compost at a rate of 32 m³/ha significantly enhanced turfgrass color and growth for 6 to 8 weeks, and increased foliar N concentrations by about 50% when compared to the control. They further reported that compost could compete with inorganic fertilizers in the ability to enhance turfgrass color and growth. Angle et al. (1) showed that the quality of the turf increased with both time and the compost amendment rate during sod establishment. The increase in quality rating was attributed to increased amounts of nutrients from the compost.

The objectives of this study were to evaluate the effects that topdressing composted manure onto established Kentucky bluegrass has on: (i) turfgrass quality, (ii) turfgrass growth rates, and (iii) root mass and distribution.

Topdressing Composted Manure onto Kentucky Bluegrass Plots

The compost used was produced from organic dairy cattle manure, obtained from Colorado Compost in Windsor, Colorado. The density of the compost was 959 kg/m³. The analysis of the compost is presented in Table 1.

Table 1. Analysis (dry weight basis) of composted manure applied via topdressing to ‘Nuglade’ and ‘Livingston’ Kentucky bluegrass.

This experiment was set up at the Colorado State University Horticulture Research Farm, located in Fort Collins, CO. The study site has a Nunn clay loam (fine, smectitic, mesic Aridic Argiustolls). The climate is semi-arid with an average annual precipitation of 365 mm. There were 24 plots (each measuring 1.2 by 1.8 m) arranged in a randomized complete block design with three blocks. Within each block, eight factorial treatments, i.e., 2 cultivars (Livingston and Nuglade) of Kentucky bluegrass (Poa pratensis, L.) and four compost treatments, were randomly applied to eight plots. All cultivar × compost treatments were replicated three times. Livingston and Nuglade Kentucky bluegrass plots were initially established using a seeding rate of 74 kg/ha in the fall of 1998. Between 1999 and 2002, fertilization at 148 kg of N per ha was applied annually.

Before any compost treatments were applied, all plots were core aerated using a Toro Greens Aerator (model 09120) with tine spacing at 6.4 cm wide × 5.7 cm long. Following core aeration, compost treatments (0, 33, 66, and 99 m³/ha) were applied via topdressing. When topdressing compost onto the turfgrass, a known volume of compost was spread onto the turf surface as evenly as possible, then swept into the grass and aeration holes with a broom. These treatments were applied in May 2003, September 2003, and May 2004.

From the beginning of May through the end of September in 2003 and 2004, irrigation was applied twice weekly, delivering 4.1 cm of water per week. The irrigation water had an electrical conductivity (EC) of 2.8 dS/m and sodium adsorption ratio (SAR) of 1.8 (Table 2). Other chemical properties are shown in Table 2. Approximately 50 kg of NO₃-N per ha was added to the turf from the irrigation water annually.

Table 2. Water analysis report of irrigation water used for the experiment.

To make all treatments balanced in inorganic nitrogen (IN), the compost was analyzed for both nitrate nitrogen and ammonium nitrogen (NO₃-N + NH₄-N) contents in the Soil, Water, and Plant Testing Laboratory at Colorado State University (Table 1). This analysis showed that treatments 33, 66, 99 m³/ha received inorganic N at 18, 36, and 54 kg/ha/yr, respectively. However, this does not take into account the slow break down and release of N from organic sources in the compost. Urea (46-0-0) was applied at rates of 61, 38, and 19 kg of N per ha/yr to treatments 0, 33 and 66 m³/ha respectively, to help balance inorganic N rates. Table 3 represents all sources of N applied during the experiment and shows total inorganic nitrogen (TIN) applied. The total P applied from compost was 86, 172, and 258 kg/ha and the total K applied from compost was 456, 911, and 1367 kg/ha for treatments 33, 66, and 99 m³/ha, respectively. The control plots did not receive any supplemental P or K during the duration of the experiment.

Table 3 Nitrogen sources applied to Kentucky bluegrass during 2003 and 2004 growing seasons.

 ^x Totals were derived by combining all sources of inorganic N.

Turfgrass Evaluation

Visual turf quality was rated monthly throughout the experiment based on color, density, and uniformity using a scale of 1 (brown, dead turf) to 9 (optimum color, dense, and uniform turf), with a rating of 6.0 or higher indicating acceptable quality.

Plots were mowed once a week during the growing season at a height of 6.4 cm. Clippings were collected four times per growing season to determine clipping yield as an indication of shoot growth. The rest of the time the clippings were allowed to recycle into the turf.

Roots of Nuglade plots were sampled in early September of 2003 and 2004 using a truck-mounted Giddings Hydraulic Soil Probe (#15-SCS Model GSRPS, Giddings Machine Company Inc., Windsor, CO), at depths of 0 to 12.5, 12.5 to 25, 25 to 37.5, and 37.5 to 50 cm using a 5.5-cm diameter probe. Samples were placed in zip-lock plastic bags and placed in a cooler. A hydro-pneumatic elutriation system was used to wash and separate the roots from the soil (20). After all the roots were collected, tiny pebbles and rhizomes were hand-removed with tweezers. The roots were then placed in an oven at 70°C for 48 h, and root dry mass was determined by weighing.

Effects of cultivar, compost treatment, and their interaction were determined using analysis of variance according to the general linear procedure of the Statistical Analysis System (SAS Institute Inc., Cary, NC). Analysis of variance test indicated that the compost treatment and cultivar interaction was not significant. Therefore, data of two cultivars were combined. Turf quality, clipping yield, and root mass were subjected to analysis of variance using SAS Proc GLM to test effects of compost treatments within individual dates. Means were separated using a protected LSD at P < 0.05.

Topdressing Compost Manure Increased the Overall Quality and Clipping Yield of Kentucky Bluegrass

Average turf quality of ‘Nuglade’ and ‘Livingston’ Kentucky bluegrass over two growing seasons (from May 2003 to January 2005) is shown in Figure 1. The compost treatment at 99 m³/ha had better quality than the control throughout the course of the experiment except in June and December 2004. Similar results occurred with compost treatment at 66 m³/ha. At the beginning of the experiment there was no difference in quality between 66 m³/ha compost treatment and the control. Starting in July 2003 and to the end of the experiment, the compost treatment at 66 m³/ha consistently had better quality compared to the control. Although inferior to the 66- and 99-m³/ha compost treatments, compost topdressing at 33 m³/ha improved turf quality from August 2003 to January 2004 and from April to September 2004. The better turf quality of compost treatments during the late fall and early spring was mainly due to better fall color retention and early spring green up.

Fig. 1. Average turf quality of 'Nuglade' and 'Livingston' Kentucky bluegrass from June 2003 to January 2005. Ratings are means of three replicates. Bars indicate least significant difference (LSD) for individual dates at P < 0.05. Arrows indicate compost applications.

In general, there is a trend of increasing turf quality as topdressing compost increased from 0 to 66 m³/ha. As the compost topdressing rate increased from 66 to 99 m³/ha, no significant improvement in turf quality was observed. Based on this research, we recommend topdressing composted manure to turfgrass at an optimum rate of 66 m³/ha. Although the highest rate at 99 m³/ha also had similar characteristics, there is no reason to apply more when the same results can be achieved with a lower application rate.

The increase in quality rating by compost topdressing was attributed to the amounts of nutrients that the compost provided to the turf (1). The optimal compost topdressing rate of 66 m³/ha found in this study is much higher than the application rate recommended for biosolid compost. Garling and Boehm (10) reported topdressing biosolid compost at 32 m³/ha increased turfgrass color and growth for up to 5 to 8 weeks. The higher optimal application rate of manure compost than biosolid compost was resulted likely because manure compost has low total N and P content (Table 2).

Clippings were collected four times during each of the 2003 and 2004 growing seasons as a means of quantifying growth. There was no difference in the clipping yield for either clipping collected in June 2003 (Fig. 2). However, in July 2003 the 66- and 99-m³/ha compost treated plots had 47% higher clipping yield compared to the control. In early August 2003, the 66- and 99-m³/ha compost treated plots yielded 30% and 46% more growth than the 33-m³/ha treatment, and had 53% and 71% higher clipping yield than the control, respectively. The 33-m³/ha compost treatment plot yielded 18% higher clipping yield than the control.

Fig. 2. Average clipping yield (g/m2/wk) of 'Nuglade' and 'Livingston' Kentucky bluegrass during growing seasons 2003 and 2004. Bars labeled with different letters were significantly different at P < 0.05.

The same pattern was observed in 2004, with no significant difference in clipping yield during the first two samplings. In late July, compost treatments of 66 and 99 m³/ha increased clipping yield by 45% and 53% compared to the control and by 15% and 22% compared to the 33-m³/ha compost treatment, respectively. In August, the 66- and 99-m³/ha treatment yielded 33 to 48% more clippings than the 33-m³/ha treatment and 48 to 65% more than the control.

No significant differences in root mass existed among any of the treatments at any of the sampled depths in the fall of 2003 or 2004. There was also no difference between years. However, it was very apparent that the majority of the roots were distributed in the 0- to 12.5-cm depth. As expected, root mass dropped drastically in deeper depths. Turfgrasses have fibrous root systems with most of the roots being in the upper 10 cm of the soil (19).

The reason that the compost treatments had higher quality and increased growth throughout most of the experiment is likely due to a fertility effect. Nitrogen is the key element due to its influence on color, growth rate, and density (14). A study conducted in Nebraska by Eghball and Power (6) estimated that the fraction of organic N mineralized in a cornfield in the year of application was about 18%. If this estimate were applicable to our current study, then about 71, 142, and 213 kg of N per ha were released from organic N of compost in 2003 from the 33-, 66-, 99-m³/ha treatments, respectively. It is believed that compost treatments provided additional long-lasting N through the organic form of N that mineralized over time. Bilgili and Acikgoz (2) showed that turf color and quality were associated with N fertility treatments, and that increasing N significantly enhanced the color and quality ratings of several turf mixtures. In addition, it has been shown that N applications in fall increased winter and early-spring coloration as compared to an unfertilized control (2,15), which is in agreement with the findings of this study.

Besides nitrogen, other essential elements, especially phosphorus (P) and potassium (K) present in the compost might have also played a role in overall quality. Phosphorus and K were not applied in control with a synthetic fertilizer, but substantial amounts were present in the compost (Table 2). Since phosphorus and potassium availability from manure compost is high (ranging from 52% to 100%) (8), we expect substantial amounts of P and K in the compost became plant-available after application. This assumption is supported by soil K and P tests conducted at the end of the study (data not shown). At the termination of the study, surface (0 to 10 cm depth) soil P increased from 1.4 mg/kg (very low) to 4.3 mg/kg (medium level) and K increased from 340 mg/kg to 840 mg/kg with 66 and 99 m³/ha compost treatments.

The compost provided P and K to the turf, which could have improved the overall quality, compared to the control. Phosphorus is the second most essential element for plant growth and it is involved in the transfer of energy as the organic compound, adenosine triphosphate (ATP), during metabolic processes. Potassium is directly involved in maintaining the water status of plants, turgor pressure of cells, and the opening and closing of stomata. However, due to the high P and K content in composted manure, repeated application over time may result in increased soil salinity, and continued P accumulation in the soil may possibly increase P runoff.

Conclusions

Topdressing compost at rates of 66 and 99 m³/ha significantly increased the overall quality throughout most dates of the two-years-study. Composted manure applications allowed Kentucky bluegrass to retain color in the fall and early winter and green up faster in the spring. Additionally, compost-treated plots produced higher clipping yields, compared to the control. These results suggest that compost act as a slow-release fertilizer, providing nutrients throughout the growing season. However, compost treatments did not increase root mass as originally hypothesized. Based on this research, we recommend topdressing composted manure to turfgrass at an optimum rate of 66 m³/ha.

Acknowledgment

The research was supported by the Colorado Agricultural Experimental Station (Projects 685 and 780).

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