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a Central Mississippi REC, Mississippi State Univ., 1320 Seven Springs Road, Raymond, MS 39154
b Agronomy Dep., P.O. Box 110300, Univ. of Florida, Gainesville, FL 32611-0300
c Statistics Dep., P.O. Box 110339, Univ. of Florida, Gainesville, FL 32611-0339
d Soil and Water Sci. Dep., P.O. Box 110510, Univ. of Florida, Gainesville, FL 32611-0510
e Dep. of Animal Sciences, P.O. Box 110920, Univ. of Florida, Gainesville, FL 32611-0920
* Corresponding author (bmacoon{at}ra.msstate.edu)
Received for publication October 8, 2001.
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ABSTRACT |
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 TOPNOTES ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARY AND CONCLUSIONSREFERENCES |
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Abbreviations: BR, bermudagrass–rye • CBR, corn–bermudagrass–rye • CP, crude protein • CPR, corn–rhizoma peanut–rye • CSR, corn–sorghum–rye • DM, dry matter • IVOMD, in vitro organic matter digestibility • NDF, neutral detergent fiber • PR, rhizoma peanut–rye
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INTRODUCTION |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARY AND CONCLUSIONSREFERENCES |
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To recycle nutrients through land application of dairy waste effluent requires the use of crops capable of utilizing these nutrients. Ideally, crops selected for such systems should have potential for high biomass yield with relatively high N uptake capacity, tolerance for wet soil conditions, prolonged vegetative growth, and tolerance to frequent harvests (Schmitt et al., 1999; Geber, 2000). High N uptake combined with high biomass production is important for N removal. Prolonged vegetative growth reduces the risk of leaching when irrigating with effluent, while repeated harvests maintain active nutrient uptake by the crop. Deep-rooting, perennial rhizomatous species have been used with good results (Schmitt et al., 1999; Geber, 2000; Sanderson et al., 2001).
Forage crops are well suited for nutrient capture and biomass production in an integrated system. There are benefits to the dairy production enterprise from forage-based cropping systems because importation of forages and the amount of concentrate fed to dairy cows are potentially reduced. Both situations result in reduction of the amount of nutrients imported to the farm. Climatic conditions in Florida allow year-round crop production, thus allowing more flexibility in effluent waste application compared with dairy production systems in temperate areas. For silage production, dairy producers in north-central Florida commonly grow crop rotations involving corn followed by sorghum during the warm months with rye as a cool-season crop. ‘Tifton 85’ bermudagrass (Burton et al., 1993) may also be a suitable forage component of dairy production systems (West et al., 1997). Rhizoma peanut is considered a good candidate for forage-based dairy production systems in Florida, given its outstanding nutritive value and response to irrigation (French and Prine, 1991) and high animal performance potential (Sollenberger et al., 2000).
Cropping systems including these crops should be evaluated under effluent application to examine nutrient capture and forage production potential. Thus, this study evaluated DM yield, crude protein (CP) concentration, in vitro organic matter digestibility (IVOMD), and neutral detergent fiber (NDF) concentration of forages from five year-round cropping systems irrigated with dairy waste effluent at three levels of N application.
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MATERIALS AND METHODS |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARY AND CONCLUSIONSREFERENCES |
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Treatments were assigned to a split-plot experiment in a randomized complete block design with three replications. Main plots were three levels of effluent N application and subplots were five year-round forage cropping systems. Dairy effluent irrigation was applied to achieve annual target N levels of 450, 675, and 900 kg ha-1 to represent low, medium, and high effluent N treatments. The effluent was pumped directly from a lagoon system. Actual N applied via effluent at the low, medium, and high effluent N levels, respectively, was: 480, 645, and 845 kg ha-1 in Year 1; 480, 695, and 920 kg ha-1 in Year 2; 565, 750, and 985 kg ha-1 in Year 3; and 480, 660, and 895 kg ha-1 in Year 4. All five cropping systems evaluated had rye as the common cool-season crop. Two of the cropping systems consisted of a single forage as the warm-season component, namely, bermudagrass or rhizoma peanut. The other three systems had crop rotations based on corn as the first crop of the season. These were corn–bermudagrass, corn–sorghum, and corn–rhizoma peanut.
Mainplots were allocated along three semicircular land areas to coincide with the path of the irrigation system. Plot areas were located within a 180° arc of the irrigation system. Each mainplot was 15.2-m wide by 76-m long, and five subplots (15.2 by 15.2 m) were randomly assigned to the mainplots. Borders between blocks and main plots were 20 m or greater to avoid slopes and depressions within plots and to allow sufficient area to switch sprinklers on or off without affecting the even distribution of irrigation on any mainplot. Borders between blocks were occupied by a mixed sward of ‘Coastal’ and ‘Callie’ bermudagrass and borders between main plots were occupied by Tifton 85 bermudagrass. All borders were overseeded with rye during the cool season.
A five-tower Rainbow center pivot irrigation system, 200 m in length with Nelson P85A sprinklers (Nelson Irrigation Corp., Walla Walla, WA), was used to apply the dairy waste effluent and fresh water. Effluent was applied at all irrigation events to mainplots receiving the high effluent N level, at 75% of the irrigations to the medium effluent N level, and at 50% of the irrigations to the low effluent N level. A series of three irrigations to achieve these three effluent applications were done within a 2-wk period, and this series was repeated every month during the annual cycle. Irrigation was not done during the periods between last harvest of the warm-season and planting of the cool-season crop, and between harvesting of the cool-season crop and planting of corn. The mainplots that did not receive dairy waste effluent during an irrigation event were equilibrated with fresh water <2 d after effluent application to ensure approximately equal volume of irrigation water on all plots. To aid in application uniformity, irrigations were done when wind speeds were <2.2 m s-1, usually at night. Volume of irrigation applied was determined by placing six 20-L plastic containers in each mainplot. A typical irrigation resulted in 1.6 cm of water being applied to the soil surface. Effluent and fresh water samples were collected at two locations per mainplot during an irrigation by placing sterilized 20-L plastic containers ahead of the irrigation system, then pouring and acidifying (pH < 2) those samples in containers that were tightly capped and placed in ice. These were subsequently refrigerated before laboratory analysis. The samples were analyzed by the Wetlands Soils Research Laboratory, Soil and Water Science Department, University of Florida in Gainesville, FL. Protocols and procedures specified by the Florida Department of Environmental Protection (1992) were followed. Total N was determined using a Kjeldahl digestion followed by semi-automated colorimetry using a Technicon Auto Analyzer (Technicon Instruments Corp., Tarrytown, NY). Annual treatment N application for each year was computed based on volume and N concentration of waste effluent and fresh water applied in each irrigation during that year.
Tifton 85 bermudagrass was planted in early September 1995, using mature stem cuttings, on plots that included bermudagrass in the cropping system. For systems that included rhizoma peanut, the cultivar ‘Florigraze’ was planted in late August 1995 using rhizomes. Annual crops included ‘Northrup King 508’ corn, ‘Dekalb FS 25 E’ forage sorghum, and ‘Wrens Abruzzi’ rye.
Planting and harvest dates for a given annual crop were the same across systems within a year (Table 1). Harvest dates for perennial crops varied among systems and years (Table 1). An 8-m2 area was harvested within subplots to determine yield. Rhizoma peanut was harvested at a 2-cm stubble height, and bermudagrass and rye at a 3-cm stubble height. Corn and sorghum stalks were cut at a 5-cm stubble height. Fresh weight was recorded and a 2-kg subsample was dried for DM determination in a forced-air oven at 65°C. The dried subsample was ground in a Wiley mill to pass a 1-mm screen. Samples for N analysis were digested using a modified aluminum block digestion technique (Gallaher et al., 1975). Ammonia in the digestate was determined using semi-automated colorimetry (Hambleton, 1977). Crude protein (DM basis) was calculated as total N x 6.25. In vitro organic matter digestibility was determined using a modification of the two-stage procedure (Moore and Mott, 1974). Neutral detergent fiber was determined using the procedure of Golding et al. (1985). Annual and season averages of nutritive value data reported for each cropping system are weighted according to DM harvested (i.e., for each crop or harvest, nutritive value concentration was multiplied by DM harvested to determine content [in kg]; the content was then summed across crops or harvests and total content was divided by total DM harvested to calculate back to concentration). Before the last harvest each year, two independent operators visually rated percent ground cover of the perennial crops, namely bermudagrass and perennial peanut.
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RESULTS AND DISCUSSION |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARY AND CONCLUSIONSREFERENCES |
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The year x cropping system interaction occurred partly because in the CSR and CPR systems annual DM yields were not different across years, but yields of the BR and CBR systems declined after Year 2, more so in the BR system. Yield of the PR system increased after Year 1 (Table 2). In addition, mean comparisons among cropping systems within year varied. In every year, CPR and PR had lower yields than the other cropping systems (Table 2). In Year 1, total annual yield of CPR was greater than that of PR, probably due to typically slow establishment of rhizoma peanut, but yield was similar between these two systems in subsequent years. Yields were similar among BR, CBR, and CSR in Year 1, greater for BR than CBR and CSR in Year 2, then greater for CSR than BR or CBR in the subsequent years. Results for Years 3 and 4 were likely due to the decline in yield of systems including bermudagrass. Tifton 85 bermudagrass has fewer rhizomes than Coastal or ‘Tifton 44’ bermudagrasses (Burton et al., 1993), possibly resulting in lower amount of stored reserves for overwintering. Additionally, high levels of N, especially late in the season, encourage vegetative growth and reduce prioritization of assimilates to storage organs, which likely predisposes perennials to winterkill (West and Prine, 1974; White, 1973). Application of N in the current study continued throughout the growing season, and potentially compromised the persistence of Tifton 85 bermudagrass. Visual ratings of percent bermudagrass cover decreased from 100% in Years 1 and 2 to 89% for BR and 91% for CBR in Year 3, and 88% for BR and 84% for CBR in Year 4.
The differences in total annual yield among cropping systems were due largely to differences among the warm-season crops within each cropping system because there were no differences in rye yields among cropping systems. Yields of rye ranged from 4.4 to 5.0 Mg ha-1 in Year 1, 4.5 to 5.0 Mg ha-1 in Year 2, 2.6 to 4.1 Mg ha-1 in Year 3, and 3.6 to 4.5 Mg ha-1 in Year 4. These yields were similar to or greater than yields reported in other USA studies (Munawar et al., 1990; Guillard et al., 1995; Monks et al., 1997; Odhiambo and Bomke, 2000). Among the warm-season components of the cropping systems, Year 1 yield of CSR was greater than CBR, and BR yield was intermediate (Table 2). In Year 2, yield of BR was greatest, followed by CSR, then CBR. In the last 2 yr, bermudagrass yields declined and the CSR system had the greatest warm-season yields. Rhizoma peanut-based systems always had the lowest warm-season yields. Yields of Tifton 85 bermudagrass in the BR system were similar to the 3-yr average of 18.6 Mg ha-1 reported by Hill et al. (1993). In Year 1, yield of rhizoma peanut in PR system was similar to yields reported for Florigraze (Prine et al., 1981; Valentim et al., 1986), but in subsequent years, yields increased about twofold. This was probably due to irrigation provided in the current study, especially during the spring to early summer dry period.
For cropping systems in which corn was the first crop, it was evident that differences in yields among systems were mostly due to contribution of the second crop. Among the second crops in the corn-based systems, yield of Tifton 85 bermudagrass (9.0 Mg ha-1; CBR system) was greater than yield of sorghum (7.7 Mg ha-1; CSR system) in Year 1, but in subsequent years, sorghum (9.4–10.3 Mg ha-1) had greater yields than bermudagrass (4.7–7.4 Mg ha-1). Yields of rhizoma peanut (0.7, 2.5, 3.0, and 3.8 Mg ha-1 for Years 1, 2, 3, and 4, respectively) as a second crop following corn were much less than when grown as a sole warm-season crop. Yields of corn were greater for CSR than the other two corn-based systems in Years 1 and 3, but were not different among cropping systems in the other years. The yields ranged from 11.4 to 14.7 Mg ha-1 in Year 1, 10.9 to 12.6 Mg ha-1 in Year 2, 11.0 to 13.2 Mg ha-1 in Year 3, and 11.3 to 12.5 Mg ha-1 in Year 4. In Florida, corn grown on phosphatic clay with N applied at 280 kg ha-1 had a 4-yr average DM yield of 15.7 Mg ha-1 (Mislevy et al., 1991). Sorghum yields in the current study were lower than the 4-yr average of 13.4 Mg ha-1 reported in a Florida study when it was the first crop, but similar to 10.1 Mg ha-1 when it was the second crop, in a sorghum–soybean [Glycine max (L.) Merr.] rotation (Mislevy et al., 1991).
Forage Nutritive Value
Crude Protein Concentration
Annual average CP concentration was affected by year x effluent N level (P < 0.001) and year x cropping system (P < 0.001; Table 3) interactions. In the first 2 yr, CP concentration was not affected by effluent N level and ranged from 102 to 107 g kg-1 in Year 1 and 101 to 108 g kg-1 in Year 2. In Year 3, CP concentration increased from 111 g kg-1 at the low to 129 g kg-1 at the high effluent N level, and similarly it increased from 104 to 126 g kg-1 in Year 4. Both the warm-season and rye crops had a similar pattern of CP response to N level. O'Leary and Rehm (1990) reported that corn CP concentration increased quadratically with increased N fertilizer application. In that study, the maximum CP concentration was 95 g kg-1 and occurred at the first increment of N application, then decreased with further N. The reason for a CP response to level of effluent N in the last 2 yr but not in the first 2 yr of the current study is unclear.
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There were no differences in rye CP concentration among cropping systems in the first 2 yr (ranging from 112 to 118 g kg-1 in Year 1 and 83 to 89 g kg-1 in Year 2). In Year 3, rye CP was greater in the CPR system (146 g kg-1) than the other cropping systems (125–130 g kg-1), and in Year 4, the CPR system had greater rye CP (132 g kg-1) than CBR and PR (117 g kg-1 each). Rye CP concentrations of the BR (127 g kg-1) and CSR (121 g kg-1) systems were intermediate but not different from the other cropping systems. The CP concentrations of rye in the current study were higher than reported by Blevins et al. (1990) (60 g kg-1) or Odhiambo and Bomke (2000) (63–81 g kg-1) when managed as a winter cover crop. When managed as a forage, however, CP of rye (121–156 g kg-1) reported by Moyer and Coffey (2000) was similar to or higher than that of the current study. Although differences in CP were evident, the contribution of rye to differences in annual average CP concentration among cropping systems was minimal because of the low DM contribution from this component of the cropping system.
As noted with the DM yield data, the differences in annual CP concentration among cropping systems were due largely to the warm-season components. Corn CP was not different among systems within a year; thus, annual average CP differences among these cropping systems (Table 3) were due mainly to the contribution from the second crop. Corn CP ranged from 68 to 74 g kg-1 in Year 1, 69 to 71 g kg-1 in Year 2, 83 to 91 g kg-1 in Year 3, and 73 to 77 g kg-1 in Year 4. Across years, CP concentration ranged from 131 to 182 g kg-1 for bermudagrass in the CBR system, 70 to 83 g kg-1 for sorghum in the CSR system, and 133 to 151 g kg-1 for rhizoma peanut in the CPR system. In a Florida study, CP of corn was 54 g kg-1 and sorghum was 69 g kg-1 (Mislevy et al., 1991). Hill et al. (1993) reported CP of Tifton 85 bermudagrass ranging from 114 to 156 g kg-1. Although rhizoma peanut had high CP, the CPR system had lower CP than all systems but CSR. This occurred because of the low DM contribution of rhizoma peanut compared with corn. Annual or warm-season average CP of the CSR system was lowest among cropping systems because corn and sorghum had the lowest CP among all crops.
In Vitro Organic Matter Digestibility
Annual average forage IVOMD was affected by effluent N x cropping system (P = 0.021; Table 4), year x cropping system (P < 0.001; Table 5), and year x effluent N level (P < 0.001) interactions. The effluent N level x cropping system interaction occurred in part because the BR and the CPR systems responded to effluent N application, but there was no response from the other cropping systems. Annual average IVOMD of the BR system was greater at the high (587 g kg-1) than at the low (573 g kg-1) effluent N level but was intermediate at the medium level (Table 4). In the CPR system, annual average IVOMD was lower at the high effluent N level. Although these differences due to effluent N levels were detected, they are probably too small to have a major effect on animal performance. Also, differences among cropping systems were not the same across effluent N levels. At the low and medium effluent N levels, the CPR system had the greatest IVOMD, followed by the PR system, but at the high effluent N level, CPR and PR had similar IVOMD, which was greater than for the other cropping systems. There was no difference in IVOMD between CBR and CSR, and the BR system had the lowest IVOMD, regardless of effluent N level.
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Regardless of year, the BR system always had the lowest IVOMD (Table 5). Ranking of the systems varied, but CPR was consistently high and PR was high in all but the last year. The IVOMD of the warm-season components followed a similar pattern as the annual averages. These data suggest that the differences in IVOMD among cropping systems were largely due to differences among the warm-season crops.
The IVOMD results of the current study are comparable to data reported in other studies. Hill et al. (1993) reported in vitro dry matter digestibility ranging from 573 to 603 g kg-1 for Tifton 85 bermudagrass. Mislevy et al. (1991) reported IVOMD of corn was 714 g kg-1 and sorghum was 553 to 581 g kg-1. The IVOMD of Florigraze rhizoma peanut ranged from 618 to 671 g kg-1 in different years when harvested three times each year (Prine et al., 1981).
The cycle x effluent N level interaction is not described because differences in IVOMD between effluent N treatments, in addition to being inconsistent, were probably too small to affect performance of animals consuming these forages. Among effluent N levels, average annual IVOMD ranges were 599 to 608 g kg-1 in Year 1, 630 to 648 g kg-1 in Year 2, 653 to 669 g kg-1 in Year 3, and 644 to 656 g kg-1 in Year 4.
Neutral Detergent Fiber
Annual average NDF was influenced by year x effluent N level (P = 0.004) and year x cropping systems (P < 0.001; Table 6) interactions. The year x effluent N level interaction occurred because annual NDF was similar among effluent N levels in Year 1 (693–701 g kg-1) and Year 2 (661–670 g kg-1) but decreased from 647 to 631 g kg-1 in Year 3 and from 603 to 580 g kg-1 in Year 4 with increasing effluent N level. The year x cropping system interaction occurred partly because all systems but BR showed a decrease in annual average NDF with each subsequent year, and partly because the responses of CSR and CPR were not the same for all years (Table 6). Ranking of the warm-season crops within a year was almost identical to the total system averages (Table 6). There were no differences among cropping systems within years for NDF of rye (data not shown).
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SUMMARY AND CONCLUSIONS |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARY AND CONCLUSIONSREFERENCES |
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Yield and nutritive value of the cropping systems were sometimes greater with increased effluent N application, but differences among effluent N levels were small. Thus, the two higher levels of N applied in this study could not be justified based on crop responses. The choice of cropping system ultimately will be determined by its ability to minimize nutrient losses and provide satisfactory returns to the producer. In companion studies, the BR system was superior to the others in reducing nitrate leaching to ground water (K.R. Woodard et al., unpublished data, 2001). Though perhaps the best system for land application of dairy wastes, low IVOMD and high NDF present challenges to formulation of high quality rations. In addition, bermudagrass stand persistence may be negatively affected by year-round applications of high N rates in effluent and by intercropping with rye and corn. The annual crops are high in IVOMD, but because of extended periods between crops, they are inferior to the BR system in reducing N leaching. Rhizoma peanut has potential for dairy enterprises because of its high nutritive value, but being a legume, it is not likely to benefit from application of N. Furthermore, it performs poorly as a nutrient trap (K.R. Woodard et al., unpublished data, 2001) and is not well suited for effluent irrigation systems. Based on these data, effluent N rates >450 kg ha-1 yr-1 cannot be justified in terms of cropping system yield or quality. Additionally, systems based on bermudagrass yield as much and have higher CP than those based on warm-season annuals, but the IVOMD of annual forages is likely to be greater.
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NOTES |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARY AND CONCLUSIONSREFERENCES |
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REFERENCES |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARY AND CONCLUSIONSREFERENCES |
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