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TECHNICAL REPORTS

Waste Management

Five Year-Round Forage Systems in a Dairy Effluent Sprayfield

Phosphorus Removal

^a Agronomy Dep., Univ. of Florida, Gainesville
^b Soil and Water Sci. Dep., Univ. of Florida, Gainesville
^c College of Medicine, Univ. of Florida, Gainesville

^* Corresponding author (krw{at}ifas.ufl.edu)

Received for publication January 19, 2006.

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
In northern Florida, forages are grown in dairy effluent sprayfields to recover excess P. Our purpose was to evaluate five year-round forage systems for their capacity to remove P from a dairy sprayfield. The soil is a Kershaw sand (thermic, uncoated Typic Quartzipsamment). Systems included bermudagrass (Cynodon spp.)-rye (Secale cereale L.) (BR), perennial peanut (Arachis glabrata Benth.)-rye (PR), corn (Zea mays L.)-forage sorghum [Sorghum bicolor (L.) Moench]-rye (CSR), corn-bermudagrass-rye (CBR), and corn-perennial peanut-rye (CPR). Forages were grown for five 12-mo cycles. Effluent P rates were 80, 120, and 165 kg ha^–1 cycle^–1. The 5-cycle P removal was 67 kg ha^–1 cycle^–1 for BR, 54 kg ha^–1 for CBR, 52 kg for CSR, 45 kg for PR, and 43 for CPR. Removal of P by winter rye was low. There were differences in system rankings among cycles primarily due to changes in the performance of perennial forages. In the first two cycles, BR had the greatest P removal (91 kg ha^–1 cycle^–1) due to high bermudagrass yield and P concentration. In the first cycle, P removal was lowest for PR (36 kg ha^–1) because perennial peanut was slow to establish. In later cycles, P removal for BR declined because bermudagrass yield and P concentration declined. It increased for PR because peanut yield increased. The yield of corn in CBR, CPR, and CSR was consistently high but P concentration was modest (avg. 2.2 g kg^–1). Sorghum produced moderate but stable yield and had low P levels (avg. 1.8 g kg^–1). Effluent rate marginally affected the performance of most grasses. For P recovery in dairy sprayfields in northern Florida, the best warm-season forage would likely be a high yielding, persistent bermudagrass.

Abbreviations: BR, bermudagrass-rye system • CBR, corn-bermudagrass-rye system • CPR, corn-perennial peanut-rye system • CSR, corn-forage sorghum-rye system • PR, perennial peanut-rye system • UFA, Upper Floridan Aquifer

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
AS the Suwannee River flows southward through northern Florida to the Gulf of Mexico, it provides borders for four counties (Gilchrist, Lafayette, Levy, Suwannee) where the number and size of dairies have increased dramatically over the last two decades. Nearly 30% of the state's 147 000 milk cows are located within the four-county area (FASS, 2002). There is particular concern over the environmental impact of dairies in this region. Distinct hydrogeological features make the Upper Floridan Aquifer (UFA) and the Suwannee River susceptible to nutrient contamination from surface-applied dairy effluent. Most of the soils in the region are excessively to moderately drained, deep sands (Entisols). Also, the UFA is relatively close to the surface and layers above it are thin and unconfined (Andrews, 1992). These features along with a relatively high annual rainfall (1310 to 1460 mm) increase the probability that dairy nutrients will enter the UFA. Nutrients reaching the UFA often end up in the Suwannee River. During low flow, the Suwannee River is supplied with water from the UFA through springs and bottom seeps (Andrews, 1992).

On most dairies in the region, milking herds are housed in free-stall barns and dry lots where manure effluent is collected and applied to sprayfields. Forages are grown in sprayfields year-round to remove nutrients from the soil. Few studies have evaluated P removal of forage systems in dairy sprayfields. Newton et al. (1995) reported that a corn-bermudagrass (‘Tifton 44’)-rye system over a 2-yr period, removed an average of 88 and 132 kg P ha^–1 yr^–1 for respective dairy effluent P rates of 93 and 183 kg ha^–1 yr^–1. French et al. (1997) reported P removal for two warm-season forage systems receiving dairy effluent in northern Florida. A corn-forage sorghum combination removed an average of 66 kg P ha^–1 while full season perennial peanut (three harvests) removed 40 kg P ha^–1. The dry biomass yield of the corn-forage sorghum combination was 27.6 Mg ha^–1. Phosphorus concentration of the two forages ranged from 1.6 to 2.8 g kg^–1. For perennial peanut, the seasonal yield averaged 13.9 Mg ha^–1 and forage P ranged from 2.4 to 3.6 g kg^–1.

In the current study, five year-round forage systems were evaluated in a dairy sprayfield over five consecutive 12-mo cycles. There were three effluent application rates. Our objective was to assess the long term capabilities of the forage systems and their components to remove P from the soil.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
The study was conducted from 1996 through 2001 in a dairy effluent sprayfield owned by North Florida Holsteins near Bell, Florida (29°44' N; 82°51' W). Average monthly maximum and minimum temperatures and daily solar radiation for the area are presented in Fig. 1. The climate is mild temperate and the average date (50% probability) of the first freeze is 25 November and last freeze is 10 March (Bradley, 1983). The soil at the site is classified in the Kershaw series (Weatherspoon et al., 1992). It is sandy to a depth of more than 2 m. Permeability is very rapid and surface runoff is slow (Hydrologic group A). The water table is below a depth of 15 m.

View larger version (18K): [in this window] [in a new window]   Fig. 1. Monthly average maximum and minimum daily temperatures (1961–1990) and daily total solar radiation (TSR; 1955–1987) recorded at the Green Acres Agronomy Facility near Gainesville, Florida. The facility is 40 km east of the actual study site.

The center pivot was repaired in 1995. Three 15.2-m wide sections along the path of the pivot were selected to mark mainplot areas. There were 20-m wide buffer zones separating them (Fig. 2). There were a total of nine mainplots and three blocks (i.e., three mainplots per block). Each mainplot was 76 m long. Mainplots were also separated to allow for sprinkler changeover areas. Part-circle sprinklers were installed on the pivot at locations corresponding to the center of the mainplots. Sprinklers in each group were vertically offset, adjusted to deliver one stream, and set at a 140° arc. Bypass sprinklers were installed to maintain constant pressure during treatment applications. Nozzles were adjusted for each group of sprinklers so that during a complete irrigation, all mainplots received a near-equal volume of effluent. Irrigations occurred mostly at night when wind speed was <2.2 m s^–1.

View larger version (20K): [in this window] [in a new window]   Fig. 2. Sectional diagram of the dairy effluent sprayfield at North Florida Holsteins dairy in northern Florida, showing the placement of mainplots, sprinklers, and changeover areas.

To determine application volume, six 20-L containers were placed in each mainplot. During a typical irrigation, 16 mm of effluent or fresh water was applied. For nutrient analysis, effluent and fresh water were collected by placing lab-cleaned, 20-L containers ahead of the pivot. Effluent rates of P were calculated using application volumes and P concentrations in dairy effluent and fresh water. The five-cycle average P rate was 80 kg ha^–1 cycle^–1 for the low, 120 kg ha^–1 for the medium, and 165 kg ha^–1 for the high (Table 1).

In northern Florida, irrigated bermudagrass is generally harvested four to five times when grown during the entire warm season (April through October). Perennial peanut is harvested three to four times. Both perennial forages are dormant in winter. In the present study, rye was planted into CSR plots and bermudagrass and perennial peanut sod plots (BR, CBR, PR, and CPR) in late November through early December with a no-till grain drill (20-cm row spacing). In the spring, corn was planted into rye stubble of CSR and into the semi-dormant sods with rye stubble of CBR and CPR with a four-row, no-till corn planter (76-cm row spacing). The no-till planter was equipped with in-row chisels that penetrated the soil to a depth of 30 cm. Following corn harvest, forage sorghum was planted into CSR plots with the same planter. After corn harvest in CBR and CPR plots, the perennial sods were allowed to grow.

Within a cycle, an annual forage that was common among systems was planted and harvested at the same time. The mean planting date was 2 April for corn, 7 August for forage sorghum, and 1 December for rye. The mean harvest date was 16 July for corn, 8 November for sorghum, and 17 March for rye. Actual planting and harvest dates throughout the study were within 7 d of the mean date. During the warm season, the bermudagrass in BR was harvested four to five times (Table 2). Perennial peanut in PR was harvested two times in the first cycle and three times in later cycles (Table 3). Bermudagrass in CBR was harvested two times and perennial peanut in CPR was harvested once.

View this table: [in this window] [in a new window]   Table 2. Harvest dates for bermudagrass in the bermudagrass-rye (BR) and corn-bermudagrass-rye (CBR) systems during five 12-mo cycles in a dairy effluent sprayfield in northern Florida.

View this table: [in this window] [in a new window]   Table 3. Harvest dates for perennial peanut in perennial peanut-rye (PR) and corn-perennial peanut-rye (CPR) systems during five 12-mo cycles in a dairy effluent sprayfield in northern Florida.

Parameters and Methods of Analysis
This project was conducted using the standard operating procedures of the Florida Department of Environmental Protection (1992). For total P concentrations in unfiltered waste effluent and fresh water, USEPA Method 351.2 was used (USEPA, 1983). The method involves a standard Kjeldahl digestion, followed by semi-automated colorimetry using a Technicon Auto Analyzer (Technicon Instruments, Tarrytown, NY). Phosphorus analysis of forage samples utilized a modification of the standard Kjeldahl procedure (Gallaher et al., 1975), followed by automated colorimetry (Hambleton, 1977) with a Technicon Auto Analyzer.

Statistical Analysis
Data were analyzed by fitting mixed linear models (Littell et al., 1996) using the PROC MIXED procedure of SAS (SAS Institute, 1992). Effluent loading rates were main plots and forage systems were subplots. The 12-mo cycles were considered repeated measures. To make inferences about forage components within the different systems, a term to describe crop nested within systems was added to the analysis. A 0.10 significant level was used for main treatment terms because of the nature of the experiment associated with (i) the variation in soil fertility within the sprayfield before treatment initiation and (ii) fluctuation of nutrient concentration in dairy effluent. Interactions terms were considered significant at P 0.10. However if trends existed, interaction terms with P values up to 0.14 were investigated which generally entailed analyzing each cycle separately. Least squares means are reported. Pairwise comparisons of means were made with the least significant difference method using the Student t statistic at the 0.05 level of significance.

	RESULTS AND DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Year-Round Forage System Comparison
Dry Biomass Yield
Main effects of cycle and forage system on yield were significant (P < 0.01). A cycle-system interaction occurred (P < 0.01) because over the five 12-mo cycles, yield declined for BR and CBR, was maintained for CSR and CPR, and increased for PR, thereby causing system ranking within cycle to change over time (Table 4). In the first two cycles, forage systems can be separated into high (BR, CSR, and CBR) and low (PR and CPR) biomass groups. The lowest yield was measured for PR in the first cycle, but PR yield increased by 52% in the second season, a level that was maintained for the remainder of the project. There was a marked decline in yield of BR and CBR following the second cycle. The CSR system was closer to maintaining high biomass yield throughout the five cycles than the other systems. A cycle-effluent rate interaction also occurred (P < 0.01) in the overall analysis because yield increased as effluent rate increased in the second cycle (P = 0.06). The rate effect was not detected in other cycles.

Phosphorus Removal
Main effects of cycle and system were significant for P removal (P < 0.01). There were cycle-system and cycle-rate interactions (P < 0.01). The BR system removed the greatest amount of P (avg: 91 kg ha^–1) in the first two cycles (Table 6), a result of high biomass yield and P concentration. The next highest P removals were measured for the CSR and CBR systems (60 to 74 kg ha^–1) while the lowest removals were from CPR and PR (36 to 49 kg ha^–1). System ranking changed in later cycles which caused the cycle-system interaction in the overall analysis. Following the first two cycles, P removal declined for all systems except PR. The greatest decline occurred in the BR and CBR systems due to substantial reductions in both yield and P concentration. For CSR and CPR, P removal was less in later cycles primarily because of lower P concentration. The cycle-rate interaction occurred because the rate effect was significant in the first and third cycles (P 0.08) but not in other cycles.

Bermudagrass in Bermudagrass-Rye System and Corn-Bermudagrass-Rye System
In the first two cycles, bermudagrass of BR had high dry matter yield and forage P concentration (Table 8), resulting in the highest P removal among warm-season forages or forage combinations. However, both yield and P concentration declined over the latter three cycles, resulting in a substantial decline in P removal. At the start of the fourth cycle (1999–2000), bermudagrass showed signs of weakening with some stand loss which was most evident in plots receiving the high effluent rate. Estimates of bermudagrass coverage on 28 May 1999 were 96% for the low rate, 89% for the medium rate, and 79% for the high rate.

Choosing other high-yielding cultivars that are known to be persistent under intensive production may improve the long-term performance of the BR system in northern Florida. At a much colder location (North Carolina, USA; 35°52' N; 78°47' W), Burns et al. (1990) applied three rates of swine effluent to Coastal bermudagrass over an 11-yr period (1973–1983). The low effluent rate averaged 356 kg N and 147 kg P ha^–1 per season, the medium rate averaged 670 kg N and 278 kg P ha^–1, and the high rate 1340 kg N and 554 kg P ha^–1. For the low rate, bermudagrass yield remained stable throughout the 11-yr period. For medium and high rates, yield remained stable from 1973 to 1976. But in 1977, yield was 32% lower for the medium rate and 44% lower for the high rate, compared with the average yield of the previous 4 yr. The yield decline resulted from some loss of stand following the severe winter of 1976–1977 (Burns et al., 1985). By 1979, the bermudagrass had recovered and produced stable yields through 1983. This study was noteworthy because Coastal bermudagrass not only survived in a much colder climate than in northern Florida but produced stable yields during 9 out of 11 growing seasons at an effluent N rate of 1340 kg ha^–1 per season.

In the current study, bermudagrass was an effective component of the CBR system for P removal in the first cycle. The dry matter yield of bermudagrass was intermediate to that of corn in CBR, CPR, and CSR, and forage sorghum in CSR in the first cycle (Table 9). As a result of higher P concentration (Table 10), P removal for bermudagrass was comparable to that of corn and 50% higher than sorghum (Table 11). In subsequent cycles, bermudagrass yield declined which was largely responsible for lower P removals. By the third cycle, there was an obvious reduction in bermudagrass stand and vigor. Reasons for the yield decline were the same as those responsible for declining performance of bermudagrass in BR. However, the decline in bermudagrass yield in CBR became apparent earlier in the project compared with the bermudagrass in BR. The CBR system exerts a great deal of stress on the bermudagrass component which accentuates problems with persistence. After corn harvest, the weakened bermudagrass must quickly re-establish, produce high yield, and allocate adequate energy reserves to below-ground plant structures before the first winter frosts, if it is to maintain high P removals and persist over multiple seasons. Over the last three cycles, P removal for bermudagrass in CBR averaged only 11 kg ha^–1 per cycle. These results show that Tifton 85 bermudagrass was not an acceptable perennial component for triple cropping systems in dairy sprayfields in northern Florida. It is possible that other bermudagrass cultivars may survive for longer periods; however, persistence is not favored because of the abusive nature of the CBR system and the high effluent N rates often applied in dairy sprayfields.

Dry matter yield of perennial peanut in CPR continued to increase during the study (Table 9). This is clearly a demonstration of its ability to survive under adverse conditions. Florigraze perennial peanut is known to be persistent, an attribute generally associated with its extensive rhizome system. There are more specific features responsible for its survival in CPR. Research has shown Florigraze to be tolerant of moderate shading (Johnson et al., 1994). Also, Saldivar et al. (1992) found that during the cooler autumn months, photosynthate produced in the shoots of Florigraze was partitioned into rhizome growth. Though the perennial peanut of the current study persisted in CPR, yield, P concentration (Table 10), and P removal (Table 11) were unacceptably low. Therefore, it is not recommended as a component for triple cropping systems in dairy sprayfields.

Corn in Corn-Forage Sorghum-Rye Sytem, Corn-Bermudagrass-Rye System, and Corn-Perennial Peanut-Rye System
In general, the performance of corn did not differ between CSR, CBR, and CPR systems (Table 9). Forage dry matter yield was stable over the first four cycles, averaging 12 Mg ha^–1 cycle^–1. Phosphorus concentrations were in the low to moderate range (1.9 to 2.6 g kg^–1; Table 10). Phosphorus removal for corn was fairly stable over the first four cycles, ranging from 22 to 32 kg ha^–1 (Table 11). For unknown reasons, yield, P concentration, and P removal were lower in the 2000–2001 cycle.

During the first half of the warm growing season, corn contributed relatively high yield to the overall biomass production of CSR, CBR, and CPR. Its main disadvantage was modest forage P concentration. High yield and modest P concentration resulted in moderate P removals. In the first two cycles, P removal for corn (avg: 30 kg ha^–1) was lower than one half of the P removal of full-season bermudagrass in BR (avg: 76 kg ha^–1) but greater than that of perennial peanut in PR (avg: 25 kg ha^–1; Table 8). Over the last three cycles, P removal of corn (avg: 22 kg ha^–1) was similar to one half removal of bermudagrass in BR (avg: 42 kg ha^–1) and greater than that of perennial peanut in PR (avg: 34 kg ha^–1).

Sorghum in Corn-Forage Sorghum-Rye System
Overall, dry matter yield, P concentration, and P removal were lower for forage sorghum than corn (Tables 9, 10, and 11). Phosphorus removal ranged from 14 to 18 kg ha^–1 cycle^–1. A positive attribute of sorghum was that its moderate yields were fairly stable over time. Its primary disadvantage was low forage P concentration. In the first three cycles, the dry biomass yield of the corn-forage sorghum combination was comparable to that of full-season bermudagrass in BR (Tables 8 and 9). However, the greater P concentration in bermudagrass during that period was responsible for its greater P removal over the corn-sorghum combination.

Effect of Effluent Rate on Forage Performance
Effluent rate did not affect the yield, P concentration, or P removal of perennial peanut in PR or CPR. However, there was a marginal impact of effluent rate on some response variables of most grass components.

Dry Matter Yield
Yield differences among effluent rates were detected for winter rye (all systems) and bermudagrass in BR and CBR, but not for corn or forage sorghum. For rye, the effect of rate on yield was significant (P = 0.09); however, there was a cycle-rate interaction (P < 0.01). For all systems, rye yield increased with rate in four of the five cycles. Average yield was 3.5 Mg ha^–1 cycle^–1 for the low rate, 3.9 Mg for the medium rate, and 4.5 Mg for the high.

A main effect of effluent rate on the yield of bermudagrass in BR was not detected. The computed P value for the cycle-rate term was 0.13. Further analysis showed that yield was affected by rate in the last cycle (P = 0.10), but not in the other cycles. In that cycle, yield from bermudagrass plots receiving the high effluent rate was lower than those receiving low and medium rates. Mean yields were 16.5, 16.8, and 13.6 Mg ha^–1 cycle^–1 for the low, medium, and high rates, respectively. For bermudagrass in CBR, the negative effect of higher effluent rates on yield became evident earlier in the study. With the first two 12-mo cycles excluded from the analysis, the rate effect on yield was significant (P = 0.07) with no cycle-rate interaction. Over the last three cycles, yield was higher in low rate plots compared with medium and high rate plots. Mean yield was 6.4 Mg ha^–1 cycle^–1 for the low rate and 4.2 Mg ha^–1 for both the medium and high rates.

Phosphorus Concentration
The effect of effluent rate on P concentration in rye forage approached significance (P = 0.12). There was a cycle-rate interaction (P < 0.01). In three of the five cycles, P concentration was higher for the medium and high effluent rates compared with the low rate (Table 12). The five-cycle mean concentration was 3.0, 3.1, and 3.2 g kg^–1 for the low, medium, and high rates, respectively.

For corn in CBR, CPR, and CSR, the effect of rate was significant (P = 0.02), but there was a cycle-rate interaction (P = 0.09). Further analysis showed that the interaction occurred because P concentration was unaffected by rate in the first cycle. With the first cycle excluded from analysis, the computed P value for the rate effect was <0.01. Over the latter four cycles, P concentration decreased as effluent rate increased (Table 12). Mean concentrations were 2.3, 2.1, and 1.9 g kg^–1 for the low, medium, and high rates, respectively. Similarly, effluent rate had a negative influence on P concentration of sorghum in CSR (P = 0.09). Means for the last four cycles were 1.8, 1.7, and 1.6 g kg^–1 for the low, medium, and high rates, respectively.

Phosphorus Removal
For rye, the effect of rate on P removal approached significance (P = 0.11) in the overall analysis. There was a cycle-rate interaction (P < 0.01). The interaction occurred because the influence of rate varied among cycles. Winter rye was the only system component in which P removal mostly increased with effluent rate, a result of a general increase in yield and P concentration. Five-cycle means for P removal were 10, 12, and 15 kg ha^–1 cycle^–1 for the low, medium, and high rates, respectively.

For bermudagrass in BR, a rate effect was detected only in the last cycle (P = 0.03) where P removal declined as effluent rate increased. Mean P removal was 39, 33, and 28 kg ha^–1 for the low, medium, and high rates, respectively. For bermudagrass in CBR, similar results occurred. Average P removal for the last cycle was 14, 8, and 10 kg ha^–1 for the low, medium, and high effluent rates, respectively. For corn in CSR, CPR, and CBR and sorghum in CSR, the effect of effluent rate on P removal was not detected.

Most studies involving increasing rates of animal waste nutrients on tropical grasses have reported a yield increase that parallels a similar increase in P removal. Generally, forage P concentration was unaffected or declined with fertilization rate. Adeli and Varco (2001) applied swine effluent P rates averaging 30, 61, and 92 kg ha^–1 to Johnsongrass [Sorghum halepense (L.) Pers.] over a 2-yr period. In both years, there was a quadratic increase in P removal, a trend that coincided with that of yield. Forage P concentration declined linearly in the first year but was unaffected in the second year. Adeli et al. (2003) applied swine effluent P rates averaging 37, 75, 113, and 154 kg ha^–1 to ‘Alicia’ bermudagrass over a 2-yr period. Phosphorus removal increased quadratically as rate increased, which coincided with a similar increase in yield. Forage P concentration was not affected by effluent rate and ranged from 1.8 to 2.6 g kg^–1. With a ryegrass (Lolium multiflorum L.)-‘Coastal’ bermudagrass system, Evers, (2002) applied 9 Mg ha^–1 of broiler litter (330 kg N ha^–1 and 190 kg P ha^–1) in the fall with a varying number of commercial N applications made throughout the remainder of a 12-mo cycle. Phosphorus uptake was directly related to forage yield. Forage P concentration was inversely related to the amount of N applied. Forage P concentration ranged from 3.8 to 7.7 g kg^–1 for ryegrass and 1.2 to 4.6 g kg^–1 for bermudagrass. Burns et al. (1985) and Burns et al. (1990) reported increasing yield of Coastal bermudagrass receiving three aforementioned rates of swine effluent over an 11-yr period. Yield increased with effluent rate in 10 of 11 yr. Contrary to current results, forage P concentration increased with effluent rate. Over the first 6 yr, mean concentration was 3.0, 3.1, and 3.4 g kg^–1 for the low, medium, and high effluent rates, respectively.

	CONCLUSIONS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
The current study clearly shows that the choice of system and its components was largely responsible for differences in yield, P concentration, and P removal. In general, effluent rate had marginal or no effect on the three response variables of system components. Therefore, forage species that produce high, stable yield and have high, inherent P concentration should be selected for P recovery in dairy sprayfields. In northern Florida, a persistent, full season bermudagrass is likely the best warm-season option. Perennial peanut was not recommended for dairy sprayfields. The major factor limiting the recovery of P by corn and forage sorghum was low forage P. Phosphorus recovery by the corn-forage sorghum combination could be improved by using high-yielding hybrids that have been selected for high forage P. Though effluent rate generally increased yield and forage P of winter rye, its recovery of P continued to be low. The reduced daily incoming radiation during the winter months in Florida is partly responsible for the low performance.

	ACKNOWLEDGMENTS

 
This project was funded through the Florida Department of Environmental Protection, Tallahassee, Florida, by a Section 319 NPS Management Implementation Grant from the United States Environmental Protection Agency. We are grateful to Mr. Don Bennink, owner of North Florida Holsteins, Inc. and his managers and staff for their active involvement in this project and donation of time, equipment, irrigation system, and land. We recognize contributions made by Mr. Winston Tooke, Natural Resource Conservation Service, USDA, who long before the initiation of this study, identified specific research needs and assisted in grant procurement.

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 

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