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a Soil and Crop Sciences Dep., Texas A&M University, College Station, TX 77843-2474
b Agricultural Engineering Dep., Texas A&M University, College Station, TX 77843-2474
* Corresponding author (dvietor{at}tamu.edu)
Received for publication February 19, 2001.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Abbreviations: DP, dissolved phosphorus • TKN, total Kjeldahl nitrogen
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Despite agronomic advantages of sludge and manure applications on turfgrass, nutrient concentrations can increase near the soil surface (Vitosh et al., 1973; Kingery et al., 1994; Lund and Doss, 1980). The accumulations of manure and fertilizer sources of P near the soil surface could be transported as sediment-bound or dissolved P in surface runoff (Austin et al., 1996; Kingery et al., 1994; Romkens et al., 1973; Vitosh et al., 1973). In a previous study of turfgrass, Linde et al. (1995) reported an inverse relationship between plant density and sediment loss. Similarly, Gross et al. (1991) observed less sediment loss at dense compared with sparse seeding rates of turfgrass. The relatively large plant densities of turfgrass could reduce sediment and associated nutrient loss in runoff compared with grasslands used for grazing and forage production (Romkens et al., 1973).
Large nitrate N (NO3–N) concentrations in soil can similarly contribute to losses through surface runoff. In addition, inorganic N in fertilizer applications is soluble in water and readily transported in water flow over and through soil. Linde and Watschke (1997) indicated that NO3–N losses in runoff were largest in initial runoff events after fertilizer applications. The runoff losses decline as fertilizer N dissolves and infiltrates with water into soil (Schuman et al., 1973). Unlike fertilizer N, organic N in manure is released slowly through mineralization and nitrification processes. Slow release of the manure N could minimize the portion of N applied on turfgrass that is transported in water, compared with inorganic N sources.
The use and export of manure sources of nutrients through turfgrass sod production has been proposed as a practice for reducing P loads on watersheds containing large densities of animal feeding operations (Griffith, 2000). Sod harvest can remove and reduce P concentrations near the soil surface, but potential losses of P and N after surface applications of manure on turf need to be evaluated. The objectives of this study were to (i) evaluate turf quality and P and N concentrations of turfgrass clippings and soil in response to increasing rates of P and N in dairy manure and inorganic fertilizer, (ii) compare volumes and P and N concentrations of surface runoff between manure and inorganic fertilizer treatments, and (iii) relate the rate and source of applied P and N to losses in surface runoff.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Applications of composted dairy manure and inorganic fertilizer comprised five treatments on the slope of bermudagrass. Three replications of the treatments were distributed along the slope in a randomized complete block design during monitoring periods in 1998 and 1999. The treatments were control (no P), 50 and 100 kg P ha-1 as manure, and 25 and 50 kg P ha-1 as inorganic fertilizer for each monitoring period. Experimental results were analyzed as a split-split plot arrangement of the experimental design. The two monitoring periods (1998 and 1999) were main plots, nutrient sources were subplots, and nutrient rates were sub-sub plots within three replications. A single control plot was included in each replication.
Dairy manure was analyzed before application with methods of the Texas A&M Soil, Water and Forage Laboratory (Parkinson and Allen, 1975). Total P and N concentrations in composted manure averaged 5.0 and 15.5 g kg-1, respectively. The rates of total P, applied as composted dairy manure, were two times those applied as inorganic fertilizer to compensate for the smaller proportion of soluble P in manure. The inorganic P in fertilizer was assumed completely soluble after prills were applied on the plot surface. The rates of P applied as inorganic fertilizer maintained or increased extractable soil P concentrations above 40 mg kg-1 and similar to the P levels in more than 70% of soil samples submitted from selected urban counties of Texas (Provin, unpublished data, 2001).
Specified P rates were broadcast on the turf surface as composted dairy manure or inorganic P fertilizer at the start of monitoring periods in June 1998 and March 1999. In addition to P, inorganic N [100 kg N ha-1 as (NH4)2SO4] was applied to the two inorganic fertilizer treatments. The N rate for each period was split between broadcast applications before runoff monitoring started and applications 61 and 40 d later during the respective monitoring periods in 1998 and 1999.
Turfgrass Responses
Plots were clipped 3.8 cm above the soil surface when turf reached a height of 5 to 7.5 cm. The first clipping date occurred 17 d after application of both P sources during the first monitoring period. Plant uptake of nutrients was quantified through digestion, and analysis of clipping samples taken during selected mowing dates. Clipping samples were dried and analyzed for total P and N by the Texas A&M University Soil, Water, and Forage Testing Laboratory (Feagley et al., 1994; McGeehan and Naylor, 1988).
Color, density, and quality of turfgrass in plots were rated visually. The monthly ratings, starting 5 d after initial P applications, were based on a scale of 1 to 9. Brown turf was given a color rating of 1 and dark green turf was rated 9. The density of an open turf canopy with exposed soil was rated 1 and a closed canopy of tillers and leaves was rated 9. Quality ratings integrated consistency, color, density, and aesthetics into a single numerical value. Quality, density, and color ratings near 5 represented an average turfgrass that could be used for a home lawn or sod production.
Volume and Nutrient Concentration of Runoff
Total runoff volume was determined by multiplying water depth, as a proportion of the maximum, by the tank volume. Daily rain amounts were recorded for natural events at an onsite monitoring station. Rain depth for the 24-h period in which measurable runoff occurred was subtracted from the depth of runoff in tanks. After each runoff event, 500 mL was sampled after mixing the volume collected in tanks of each plot. The samples were frozen immediately to prevent microbial breakdown of nutrients within the water sample.
The particulate fraction of P and N in the 500-mL samples was removed during filtration through a 1-µm glass microfiber filter. The 1-µm pore size permitted suction filtering of the sample volume without plugging by organic and clay colloids, and total dissolved phosphorus (DP) in the filtrate could be analyzed through inductively coupled plasma optical emission spectroscopy (ICP). In addition, the glass filter disk and particulate fraction were digested to determine total P and total Kjeldahl nitrogen (TKN) (Parkinson and Allen, 1975). Total P in digests of the particulate fraction was analyzed through ICP. The TKN in the digests and the NO3–N and NH4–N of the filtrate were measured in an autoanalyzer. The NO3–N was analyzed with cadmium reduction (Dorich and Nelson, 1984) and the NH4–N was analyzed colorimetrically (Dorich and Nelson, 1983; Isaac and Jones, 1970). The NH4–N concentrations were measured in runoff of the first three events in 1998 and the initial event in 1999.
A textural analysis was completed for three soil samples taken at random across the three replications of plots on the slope. Each sample comprised 12 to 15 cores, which were 2.5 cm in diameter and 7.5 cm in depth. The soil is described as a sandy loam or sandy clay loam containing 56% sand, 24% silt, and 20% clay. The native soil, a Boonville fine sandy loam, was excavated to construct the 8.5% slope.
Each plot was sampled and analyzed prior to the initial P and N applications and after each monitoring period. Ten to fifteen soil cores (2.5 cm in diameter with a depth of 7.5 cm) were randomly sampled and mixed to provide a plot composite. Extractable P and NO3–N of the sample from each plot were analyzed by the Texas A&M University Soil, Water, and Forage Testing Laboratory. An acidified ammonium acetate (EDTA) was used to estimate plant-available P (Hons et al., 1990) and soil nitrate was extracted and analyzed with methods described by Dorich and Nelson (1984).
Statistical Analysis
The Statistical Analysis System (SAS Institute, 1988) was used to analyze variation of turf responses, runoff volumes, and P and N concentrations of runoff and soil among monitoring periods, rain events, P sources, and P rates. Numerical ratings of turf and weights and nutrient concentrations of clippings were pooled over the sampling dates of both monitoring periods for analysis. The Generalized Linear Models procedure (SAS Institute, 1988) was used to analyze variation of soil nutrients and of volume and DP, NO3–N, and NH4–N quantities for runoff filtrates. Variation of total P and TKN in particulate fractions of runoff was similarly analyzed. When interactions of effects of monitoring periods with P sources and rates were significant (P = 0.05), monitoring periods were analyzed separately. Similarly, when interactions between effects of rain events and of P sources and rates were significant (P = 0.05), rain events were analyzed separately. The P rates were treated as class variables in the statistical model.
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RESULTS AND DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Runoff Volume
Runoff volumes differed significantly (P = 0.01) among four rain events during each monitoring period and the first event did not occur until 60 d after the P applications during 1998 (Table 3)
. Asynchrony between rainfall and runoff measurements during 2 d of a prolonged rain event resulted in a runoff depth greater than the 24-h rain total for Event D in 1998. A portion of the rain recorded for Event C contributed to runoff measured for Event D. In addition, the antecedent rainfall of Event C saturated the soil and maximized the portion of rain lost as runoff during Event D.
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Nutrient Concentrations in Runoff
An interaction between rain events and P rates was significant (P = 0.01) for DP in runoff during each monitoring period (1998 and 1999). In contrast to the initial rain event in 1999, DP concentrations in runoff for the second event in 1999 and all four events during 1998 were relatively small (Table 4)
. Irrigation during the 60-d period between initial P applications on turf and the first rain event could have reduced DP concentrations at the soil surface in 1998. Conversely, the short interval between the P applications and first rain event in 1999 contributed to large DP concentrations in runoff. The reduction of DP concentrations in runoff after the initial event in 1999 was similar to previous studies of turf and pasture (Edwards and Daniel, 1994; McLeod and Hegg, 1984; Austin et al., 1996; Linde and Watschke, 1997).
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The differences in runoff concentrations of DP between P rates were largest during the initial rain event 3 d after manure and fertilizer applications in 1999 (Tables 3 and 4). In contrast to seven other rain events, differences in mean DP concentrations for this first runoff in 1999 were three times greater between the two P rates of fertilizer than between the two P rates of manure (Table 4). Similarly, differences in DP of runoff between each rate of P fertilizer and the control were three times greater than DP differences between respective smaller and larger rates of manure P and the control. In contrast to other rain events, DP concentrations in runoff from the 50-kg rate of fertilizer P were 206% larger than runoff from the 100-kg rate of manure P for this first rain event in 1999.
In a previous comparison between fertilizer and poultry litter, DP concentrations in runoff differed most during the first simulated rain event after application on tall fescue (Festuca arundinacea Schreb.) (Edwards and Daniel, 1994). Dissolved P concentration in runoff from fertilized tall fescue was two times greater than runoff concentrations after the same P rate was applied as poultry litter. The clipping height of tall fescue was 2.4 times taller than that of bermudagrass in the present study. Yet, DP concentrations in the initial runoff after application of comparable P rates were similar between the studies of tall fescue and bermudagrass (Table 4).
Similar to DP, NO3–N and NH4–N concentrations in runoff were largest during the first rain event 3 d after the manure and fertilizer applications in 1999. In addition, the N source by rate interaction was significant (P = 0.01) for NO3–N and NH4–N in runoff during this initial event in 1999. The large NO3–N concentration in the initial runoff from the larger manure rate in 1999 was consistent with 5.3 times more total N in the manure than in the initial application of 50 kg N ha-1 as (NH4)2SO4 (Table 5) . Previous evaluations of plant uptake of N during the first year after dairy manure application indicated that 21% of the N in manure was equivalent to N applied as fertilizer (Klausner et al., 1994). The relatively large NO3–N concentrations in runoff 3 d after application of the two manure rates during 1999 indicated that more than 21% of total N in composted manure was NO3–N. Unlike the first rain event, the NO3–N concentrations in runoff of fertilized treatments were significantly greater (P = 0.05) than manure treatments during rain Events B, C, and D of 1999 (Table 5). Larger NO3–N concentrations and losses in runoff from fertilizer compared with manure or organic sources of N have previously been reported (Edwards and Daniel, 1994; McLeod and Hegg, 1984).
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The initial application of (NH4)2SO4 with P fertilizer in 1999 contributed to 32 mg L-1 of NH4–N in runoff 3 d later. Similar NH4–N concentrations were observed in runoff of simulated rain shortly after N fertilizer was applied to tall fescue stands (Edwards and Daniel, 1994). During the monitoring period in 1998, NH4–N concentrations in runoff (3.2 mg L-1) 11 d after the second (NH4)2SO4 application were smaller than the initial event in 1999. Irrigation during the 11 d before the rain event could have dissolved and transported the NH4–N into soil. In contrast to observations after fertilizer applications, NH4–N concentrations in runoff shortly after composted manure applications in 1998 and 1999 were 
1 mg L-1 (data not shown). Near-zero NH4–N concentrations were observed in simulated runoff 14 d or more after poultry litter was applied to tall fescue (Edwards and Daniel, 1994).
Nutrient Losses in Runoff
The potential for removing and exporting large amounts of manure P and N through sod is an incentive for large manure rates that exceed P and N amounts needed for turf growth (Griffith, 2000). The volumes and P and N concentrations of runoff on the steep slope of bermudagrass provide estimates of potential P and N losses and environmental effects of the large manure and fertilizer rates on turf. The DP amounts in runoff differed significantly (P = 0.05) between rates and between manure and fertilizer sources during 1999. During eight rain events, the 200 kg of P in two manure applications contributed 7.1 kg ha-1 more DP to runoff than the control. A similar loss of DP in runoff was observed after two fertilizer applications totaling 100 kg P ha-1. The DP losses during eight rain events following two applications of manure totaling 100 kg P ha-1 were 3.0 kg ha-1 greater than the control and similar to two fertilizer applications totaling 50 kg P ha-1.
The portion of total P in turf clippings and runoff attributed to manure (control amounts were subtracted) was only 2.8 to 3.8% of P applied during both monitoring periods (Table 6) . Comparable percentages of P in poultry litter applications were collected in runoff during four simulated rain events on a 5% slope of perennial grass (Edwards and Daniel, 1994). The small amounts collected in clippings and runoff (Table 2) indicated that most of the P in applied manure remained on or in soil and available for harvest with sod.
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Losses of NH4–N in runoff soon after N applications revealed an advantage of manure over fertilizer applications on turf. The largest loss comprised 10.3 kg NH4–N ha-1 in runoff 3 d after 50 kg N was applied as (NH4)2SO4 in 1999. The total NH4–N losses in runoff during two rain events following N fertilizer applications were 2.9 times greater than total NO3–N losses from the larger manure rate during all eight rain events in 1998 and 1999. The NH4–N losses were 40 to 42% of total N amounts in clippings and runoff (Table 6). Similar to the NH4–N loss from fertilizer, DP losses in runoff above those of the control were 2.7 times greater for the 50-kg rate of fertilizer P than for the 100-kg rate of manure P during the first rain event in 1999.
An advantage of turf as a crop for removing manure P and N was evident in negligible losses of particulate forms of P and N after surface application of composted manure. Calculated total losses of particulate P and TKN after manure or fertilizer applications during the eight rain events in 1998 and 1999 did not differ from the control. In addition, amounts of particulate P and TKN in runoff decreased significantly (P = 0.05) in both years after the first rainfall event (Table 7) . Reductions in particulate P and TKN after the initial runoff event of each monitoring period could be attributed to increases in turfgrass plant density over time (Linde and Watschke, 1997; McLeod and Hegg, 1984). The density ratings and clipping dry weights (Table 1) indicate that additions of N fertilizer with manure P could increase plant density and minimize losses of particulate forms of P from turf. Yet, large runoff losses of fertilizer N compared with manure alone could be problematic (Table 6).
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CONCLUSIONS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Applying manure on the turf surface optimizes potential removal and export of excess P and N during harvest of the sod layer. Yet, relatively large DP concentrations and losses were observed in runoff after manure applications, which could raise concentrations of DP and accelerate eutrophication in lakes and streams (Daniel et al., 1998). The observations of runoff losses on the steep slope represent a worst-case situation, but site-specific manure rates need to be determined to minimize edge-of-field losses of P and N in runoff from sod production fields.
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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