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a USDA-ARS, Plant Genet. Resour. Conserv. Unit, 1109 Experiment St., Griffin, GA 30223-1797
b USDA-ARS, Crop Sci. Res. Lab., Waste Manage. and Forage Res. Unit, P.O. Box 5367, Mississippi State, MS 39762
* Corresponding author (gpederson{at}ars-grin.gov)
Received for publication June 1, 2001.
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ABSTRACT |
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 TOPNOTES ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Abbreviations: DM, dry matter
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INTRODUCTION |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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The concentration of Cu and Zn in animal waste varies due to the type of animal and feeding practices. Poultry and swine feeds contain greater amounts of Cu and Zn than dairy and beef cattle feeds (Nicholson et al., 1999). Utilization of these heavy metals by poultry can be relatively low. Mohanna and Nys (1999) reported that only 6% of Zn ingested by poultry is retained. Concentration of Cu and Zn in poultry litter can vary widely due to differences in poultry feed and pest control (van der Watt et al., 1994; Pesti and Bakalli, 1996). In a review article, Sims and Wolf (1994) reported mean litter concentrations vary from 32 to 593 mg Cu kg-1 in 12 studies and from 125 to 496 mg Zn kg-1 in seven studies. Amounts of Cu and Zn applied to the soil in poultry litter exceed the annual nutrient requirements of plants, with estimates of 6.6 times more Zn applied than plants require (Mohanna and Nys, 1999).
Short- and long-term applications of poultry litter increase Cu and Zn concentrations in soil, especially in the top 5 to 10 cm (Wood and Hattey, 1995; Wood et al., 1996; Han et al., 2000). Litter applications for 15 to 28 yr resulted in greater Cu and Zn accumulation down to 45 cm compared with non-litter-treated controls (Kingery et al., 1994). Concentrations averaged 2.6 and 10 mg kg-1 Cu and Zn, respectively, in the top 15 cm of soil following these long-term applications compared with 0.7 and 2.1 mg kg-1 Cu and Zn, respectively, without litter application. Plant uptake of heavy metals can be quite low, with only 0.5% of Cu and 3 to 5% of Zn applied in poultry litter taken up by sorghum-sudangrass, Sorghum bicolor (L.) Moench (van der Watt et al., 1994).
Reports of nutrient uptake from soils treated with animal wastes have considered relatively few forage species. Most studies have used a single species or mixture of species as a catch crop while evaluating other treatment variables (e.g., Vervoort et al., 1998). Abe and Ozaki (1998) reported that annual ryegrass had the greatest P and N removal rate of 11 spring-grown species in plant beds used to filter wastewater. Honeycutt et al. (1988) reported that dry matter (DM) yield of bermudagrass [Cynodon dactylon (L.) Pers.], tall fescue (Festuca arundinacea Schreb.), and a tall fescue–red clover (Trifolium pratense L.)–white clover (T. repens L.) mixture was increased with increasing rates of poultry litter. Plant N and P uptake increased with rate of poultry litter application on bluegrass (Poa pratensis L.)–tall fescue and bermudagrass–tall fescue pastures (Lucero et al., 1995; Vervoort et al., 1998). Long-term litter application on tall fescue pastures increased plant N, P, and K concentration (Kingery et al., 1993). Forages, such as tall fescue, have been promoted for use as vegetative filter strips on litter-fertilized sites to decrease runoff containing heavy metals (Edwards et al., 1997; Sauer et al., 1999). However, tall fescue grown in pastures with a history of long-term litter application had similar Cu and Zn concentrations as fescue grown in pastures without litter application (Kingery et al., 1994). There is a wide range of forage species that are adapted for growth in the southeastern USA (Ball et al., 1991), but little is known about the nutrient uptake of these species under poultry litter fertilization.
Distribution of nutrients within plant parts varies among species. Nitrogen (crude protein) concentration was lowest in leaves and highest in stems of subterranean clover (T. subterraneum L.) in comparison with three other clovers (Brink and Fairbrother, 1992). Maize (Zea mays L.) lines selected for improved P uptake had larger root systems with greater P accumulation than lines with lower P uptake rates (Ciarelli et al., 1998). Increases in P supply decreased the root/shoot ratio in three of four forage legumes (Hart et al., 1981). Management can also alter nutrient uptake by the modification of variables such as litter application rates, application time, or plant maturity at harvest.
Annual ryegrass is most commonly grown for winter pasture and is sometimes used for hay and silage in the southeastern USA, often overseeded on bermudagrass (Ball et al., 1991). The objectives of this study were to (i) compare N, P, K, Cu, and Zn concentration, uptake, and distribution in roots, stems, leaves, and flowers of annual ryegrass with 15 other cool-season forage grass and legume species fertilized with poultry litter and (ii) determine which plant part is most important to emphasize in breeding and management efforts to maximize nutrient removal from sites fertilized with poultry litter.
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MATERIALS AND METHODS |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Seed of the 16 forages were broadcast-seeded in 2- by 5-m plots with 1-m alleys between replications in September 1996 and 1997. Seeding rates were reported in Brink et al. (2001). The study was conducted on a Savannah fine sandy loam using a prepared seedbed in a pasture at Collins, MS (31.6° N, 89.6° W). Soil chemical characteristics using the Mehlich 3 extractant (Mehlich, 1984) are presented in Table 1 along with pH in 1:1 soil/water suspension. The pasture had a history of annual broiler litter applications, with additional litter applied at 9 Mg ha-1 (N, 34; P, 20; and K, 32 g kg-1 litter and Cu, 82 and Zn, 504 mg kg-1 litter) and incorporated to about 15 cm before seeding.
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Samples were separated into roots, stems, leaves, and flowers. All remaining soil and organic matter was washed from the root system. Roots were severed from the aboveground plant parts at the junction of root and stem or stolon. Each legume flower head and grass inflorescence was separated from the stem at the point of the bottom floret. Leaves (including petioles) of legume species and leaf blades (without the leaf sheath) of grasses were removed from the stem. Stems were defined as the remaining plant part following removal of flowers, leaves, and roots. All plant parts were dried at 65°C for 48 h and weighed.
Samples were ground to pass through a 1-mm screen. Phosphorus, K, Cu and Zn concentrations were measured using an inductively coupled argon plasma emission spectrophotometer using methods given in Brink et al. (2001). Nitrogen concentration was determined by macro-Kjeldahl. Nitrogen, P, K, Cu, and Zn content of the plant parts was calculated as a product of dry weight and N, P, K, Cu, or Zn concentration, respectively. Nitrogen/P ratio was computed from the N and P content data.
Experimental design was a randomized complete block with four replicates. Data were analyzed by analysis of variance (SAS Inst., 1990). Means of annual ryegrass were compared with those of the other species by Fisher's protected least significant difference (LSD) when means were found to be significantly different by the ANOVA F-test. Unless otherwise noted, the 0.05 level of probability was used to identify differences.
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RESULTS AND DISCUSSION |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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In this study, the N concentration of annual ryegrass plant parts was less than that of all legume plant parts (Table 3). Legume stems averaged two to four times, leaves 2.5 to four times, flowers one to three times, and roots two to 3.5 times greater N concentration than annual ryegrass (Table 3). These results on plant parts support common knowledge of higher N and crude protein concentration in harvested portions of legumes compared with grasses (Minson, 1990; Ball et al., 1991). The greatest N concentration was observed in legume leaves and flowers, especially hairy vetch in 1997 and austrian winter pea leaves and flowers in 1998 (Table 3). The relative N concentration among plant parts within a legume species or comparisons among legume species were relatively consistent with previous reports (Harper, 1962; Davies et al., 1968; Minson, 1990; NRCS, 1992).
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Rye and wheat also had a greater N concentration than annual ryegrass in some plant parts. Rye leaves, wheat stems, and rye flowers had a greater N concentration than annual ryegrass in both years (Table 3). In 1997, rye stems and wheat leaves had a greater N concentration than annual ryegrass. There were no differences between annual ryegrass and the cereals for root N concentration or whole-plant N content.
Averaged over all species, leaves (34.6 g kg-1) and flowers (30.7 g kg-1) had greater N concentrations than stems (18.7 g kg-1) and roots (19.2 g kg-1). These results support previous reports that forage leaves have twice the crude protein (N concentration x 6.25) concentration of stems (Minson, 1990; Buxton and Mertens, 1995).
Phosphorus
Subterranean and white clover had greater P concentration in stems than annual ryegrass in 1997 while 8 of 12 legumes had greater P concentration in stems than annual ryegrass in 1998 (Table 4). Stems of subterranean and white clover are prostrate stolons, which are not harvested because they spread along the soil surface. Though these stolons may contain a significant P concentration, it is only a temporary sink as eventual death and decomposition will release the P back to the soil. Most literature on P concentration in forages deals with the harvested portion of the plant, which would include upright stems, leaves, and flowers. Results on harvested forage by Minson (1990) were similar to the results on stems of this study, as legumes averaged 3.2 g P kg-1 while grasses averaged 2.7 g P kg-1. These results differed from the range of forages listed by the Natural Resources Conservation Service (1992) where harvested parts of legumes averaged 2.2 g kg-1 and grasses averaged 3.6 g kg-1. Under high P fertilization, Jackson et al. (1964) reported a range of 2.6 to 4.2 g kg-1 in the harvested portion of alfalfa, white clover, subterranean clover, and red clover.
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Oat had a greater P concentration in stems than annual ryegrass in 1998 though no differences were noted among the grasses in 1997 (Table 4). Both oat and rye stems contained a greater amount of P than annual ryegrass stems in 1998.
The P concentrations in leaves of legumes and ryegrass were similar in 1997 (Table 4). In 1998, 8 of 12 legumes had greater leaf P concentration than annual ryegrass. Leaf P concentrations in the grasses were similar both years. All legumes and grasses contained similar amounts of P in 1997 and 1998.
Legume flowers generally had a greater P concentration than annual ryegrass as observed in 9 of 12 legumes in 1997 and 5 of 10 legumes in 1998 (Table 4). The greatest P concentrations noted in any plant part in this study were observed in hairy vetch flowers (8.03 g kg-1) in 1997 and austrian winter pea flowers (9.10 g kg-1) in 1998 (Table 4). However, the DM yield of legume flowers was quite low, resulting in only 0.01 to 0.36 g P m-2 in legume flowers. Only crimson clover flowers in 1997 contained more P than annual ryegrass. None of the cereal flowers had a greater P concentration than annual ryegrass in either year (Table 4) though rye flowers contained more P than annual ryegrass in 1997.
Legume roots generally had a higher P concentration than roots of annual ryegrass, with 11 of 12 legumes greater in 1997 and all 12 greater in 1998 (Table 4). The greatest P concentration in roots was observed in subterranean clover (5.36 g kg-1 in 1997 and 7.59 g kg-1 in 1998). Red clover roots contained more P than annual ryegrass in both years while subterranean clover roots contained more P in 1998.
Averaged over all species, flowers had the greatest P concentration (4.3 g kg-1), followed by leaves (3.1 g kg-1), stems (2.9 g kg-1), and roots (2.7 g kg-1). Minson (1990) reported that forage floral parts had the greatest P concentration (3.2 g kg-1), with little consistent difference in P concentration noted between stems (2.1 g kg-1) and leaves (2.2 g kg-1). In this study, due to the large amount of DM located in stems, most P was contained in stems (0.79 g m-2), followed by leaves (0.34 g m-2), flowers (0.12 g m-2), and roots (0.10 g m-2). To maximize P uptake in sites overfertilized with poultry litter, management procedures and breeding objectives should emphasize stem production to increase the DM to be harvested and removed while maintaining palatability of stems for consumption by livestock.
Potassium
There were few legumes that had greater K concentrations in stems or leaves than annual ryegrass. Stems of ball clover in both years and those of austrian winter pea, hairy vetch, and subterranean clover in 1998 had greater K concentrations than annual ryegrass stems (Table 5). Red and white clover leaves had greater K concentrations than annual ryegrass leaves in 1997 though no difference was found between the species in 1998. Hairy vetch flowers in both years and austrian winter pea and subterranean clover flowers in 1998 had greater K concentrations than annual ryegrass flowers (Table 5). The greatest difference in K concentration between annual ryegrass and the legumes was observed for roots. Eight of 12 legumes in 1997 and 11 of 12 legumes in 1998 had greater root K concentrations than annual ryegrass (Table 5).
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Few forages contained more K in plant parts than annual ryegrass (data not shown). Rye in both years (6.6 and 8.9 g m-2, respectively) and oat (9.2 g m-2) in 1998 contained more K in stems than annual ryegrass (3.8 and 4.7 g m-2, respectively). More K in roots than annual ryegrass (0.3 and 0.2 g m-2, respectively) was observed for red clover in both years (0.8 and 0.6 g m-2, respectively) and oat (0.7 g m-2) and alfalfa (0.4 g m-2) in 1998. Red clover (3.5 g m-2) contained more K in leaves than annual ryegrass (2.0 g m-2) in 1997. Rye (2.4 g m-2) and crimson clover (1.7 g m-2) contained more K in flowers than annual ryegrass (0.4 g m-2) in 1997.
Nitrogen/Phosphorus Ratio
The ideal forage species for nutrient uptake would remove N and P in the same ratio as which it is applied on the soil as poultry litter. Poultry litter has a N/P ratio ranging from 2.0:1 to 2.9:1 while the N/P ratio in crops is generally considered to average 8:1 (NRCS, 1992; Sims and Wolf, 1994; Vest et al., 1996; Patterson et al., 1998). This difference in N/P ratios between litter and crop utilization has been used extensively to illustrate the problem of P accumulation in soils that have been fertilized with poultry litter on the basis of crop N needs (Stephenson et al., 1990; Lucero et al., 1995; Marshall et al., 1998). Yet use of an average value can be misleading as the N/P ratio can be quite different between legumes and grasses or among different forage species. In a compilation of data for four legumes and 18 grasses, the N/P ratio for legumes averaged 10.4 (range 9.1–11.3) and grasses 6.1 (range 1.2–11.5) in the harvested portion (NRCS, 1992). In plant beds for wastewater treatment, the ratio of N to P removal rate for wheat and annual ryegrass was 6.5 while other forage and aquatic species averaged 5 (Abe and Ozaki, 1998).
Legumes had a greater N/P ratio than annual ryegrass in stems in both years, leaves in both years, and flowers in 1998 (Table 6). Roots of legumes did not have a greater N/P ratio than annual ryegrass. The N/P ratio presented for legumes in this study as well as others (NRCS, 1992) includes N contributed by fixation as well as uptake. Therefore, the ratio of N uptake to P uptake for legumes would be assumed to be lower, depending on the relative amount of N taken up by the plant compared with what was obtained through N fixation. None of the cereal plant parts had a greater N/P ratio than annual ryegrass plant parts.
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Copper
There were few differences among grass species for Cu concentration as only rye stems had a greater Cu concentration than annual ryegrass stems in 1997 (Table 7). Kubota (1983) also found little variability among grass species for Cu concentration. Most legumes had a greater Cu concentration than annual ryegrass in stems, leaves, and roots in 1997 and leaves, flowers, and roots in 1998. Legume Cu concentration averaged 4.5 to 6.5 times greater for stems, four times greater for leaves, three times greater for flowers, and two to three times greater for roots compared with annual ryegrass plant parts (Table 7). In a review of world literature, Minson (1990) reported that temperate legumes generally have a greater Cu concentration that temperate grasses. Red clover was observed to have a greater Cu concentration than four grass species (Fleming, 1963). Forage legume Cu concentration has been reported to be twice that of forage grasses in the USA (Kubota, 1983) and Canada (Miltmore and Mason, 1971).
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To maximize heavy-metal removal by these forages from poultry litter–fertilized sites, Cu concentration is less important than the total amount of Cu contained within the plant. The large differences observed in Cu concentration between legumes and annual ryegrass did not result in similar differences in the total amount of Cu contained in legumes and annual ryegrass. Only 4 of 12 legumes in 1997 and 2 of 12 legumes in 1998 had greater stem Cu amounts than annual ryegrass (data not shown). Similar results were noted for leaves and flowers. Grass roots averaged 1.01 and 1.81 mg Cu m-2 in 1997 and 1998, respectively, while legumes averaged 0.89 and 0.50 mg Cu m-2 in 1997 and 1998, respectively. Red clover in 1997 was the only legume to contain more Cu in roots than annual ryegrass. Annual ryegrass contained more Cu in roots than two of three grasses and 6 of 12 legumes in 1997 and two of three grasses and all legumes in 1998.
Plant Cu content was almost the exact opposite of concentration due to the large amount of DM in plant stems and leaves compared with roots and flowers. Averaged over all species, stems contained the most Cu (2.01 mg Cu m-2), followed by leaves (1.57 mg Cu m-2), roots (0.95 mg Cu m-2), and flowers (0.53 mg Cu m-2).
Zinc
Few differences were observed among the grass plant parts for Zn concentration as only rye stems and roots had greater Zn concentrations than annual ryegrass in 1997 (Table 8). Gladstones and Loneragan (1967) observed Zn concentration in rye shoots similar to that in wimmera ryegrass (Lolium rigidum Gaud.) but greater than wheat or oat shoots. Minson (1990) noted that several studies have reported large differences in Zn concentration among grasses, but these differences were not consistent among sites.
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When Zn concentrations were averaged over all species, leaves had the greatest concentration (75.4 mg Zn kg-1), followed by flowers (65.8 mg Zn kg-1), roots (65.3 mg Zn kg-1), and stems (40.5 mg Zn kg-1). Other studies have reported Zn concentrations of leaf and flower greater than those of stems for a number of grasses and legumes (Minson, 1990; Fleming, 1963).
Few differences were noted for Zn uptake between annual ryegrass and any of the other forages (data not shown). Subterranean clover leaves were the only plant part to contain more Zn than annual ryegrass in both years. Rye stems in 1997; ball, crimson, red, and rose clover leaves in 1997; and rose clover flowers in 1998 also contained more Zn than annual ryegrass. These results differ from those of Gladstones and Loneragan (1967), who observed much greater Zn uptake in legume shoots than grass or cereal shoots.
As was observed for Cu, Zn uptake was closely related to relative DM production of the different plant parts, with stems containing the most Zn (12.4 mg Zn m-2), followed by leaves (7.0 mg Zn m-2), roots (2.4 mg Zn m-2), and flowers (1.9 mg Zn m-2).
Correlations
Nitrogen, P, Cu, and Zn concentrations were highly correlated for all aboveground plant parts in both years of this study (Table 9). For roots, N, P, and Cu concentrations were correlated as well as N and K concentrations. Little consistent relationship was noted between K and P (Table 9). No correlation was found between K and P concentration for any plant part in 1997, yet in 1998, all plant parts showed a significant correlation. Strategies to improve N concentration through management or breeding should also result in increases in P, Cu, and Zn concentration. Nitrogen fertilization is one management technique known to improve N concentration in grasses. Therefore, to improve P, Cu, and Zn concentration and uptake in poultry litter–fertilized sites, it may be beneficial to apply limited amounts of N fertilizer to annual ryegrass or other grasses when N is not in excess.
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CONCLUSIONS |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Annual ryegrass is the most common winter annual forage grown in the southeastern USA. In fields fertilized with poultry litter, annual ryegrass was as effective as other forages in N, P, K, Cu, and Zn uptake. Few other species showed significant advantages over annual ryegrass for whole-plant nutrient uptake. The low N/P ratio of oat stems and greater P content in 1998 could make oat a possible alternative to annual ryegrass in some areas less sensitive to frost. The concentration of DM in stems emphasizes the importance of optimizing stem production to maximize nutrient uptake by annual ryegrass and other forages. Annual ryegrass breeding programs have usually concentrated on grazing uses with selections for disease resistance, forage quality, and variation in plant maturity (Jung et al., 1996). Selections for grazing tolerance and forage quality may result in short, leafy plants with less DM in stem production. Our results suggest that plants should be selected or managed for DM yield, with a greater proportion of their DM in stems to maximize nutrient uptake. If the end use of the forage is livestock consumption, producers need to still maintain acceptable palatability in the hay.
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NOTES |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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REFERENCES |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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