Published online 13 July 2005
Published in Agron J 97:1216-1221 (2005)
DOI: 10.2134/agronj2004.0272
© 2005 American Society of Agronomy
677 S. Segoe Rd., Madison, WI 53711 USA
Production Papers
Agronomic Response of Cool-Season Grasses to Low-Intensity Harvest Management and Low Potassium Fertility
J. H. Cherneya,b,* and
D. J. R. Cherneya,b
a Dep. of Crop and Soil Sci., Cornell Univ., Ithaca, NY 14853
b Dep. of Animal Sci., Cornell Univ., Ithaca, NY 14853
* Corresponding author (jhc5{at}cornell.edu)
Received for publication November 8, 2004.
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ABSTRACT
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Species selection, fertilization, and harvest management can have a major impact on forage K concentration, and low K is critical for nonlactating dairy cow forage. Our objective was to determine if selection of grass species, along with appropriate fertilization and harvest management, will result in minimizing forage K concentration for nonlactating dairy cows while maintaining stand persistence. Three K fertilizer treatments were applied to reed canarygrass (Phalaris arundinaceae L.), timothy (Phleum pratense L.), orchardgrass (Dactylis glomerata L.), smooth bromegrass (Bromus inermis Leyss.), and tall fescue (Festuca arundinacea Schreb.) for 6 yr on a Williamson silt loam (coarse-silty, mixed, active, mesic Typic Fragiudepts) soil type in Ithaca, NY. All grass species persisted through the completion of the experiment, without visible K deficiency symptoms. Yield of dry matter (DM) was 5.6% higher (P < 0.05) under split applications of K fertilizer compared with the 0 K fertilizer treatment. Annual K uptake was increased 17.2% with split application of K fertilizer although apparent recovery of K averaged less than 20%. Forage quality was not greatly impacted by K fertilization although the K concentration of forage increased by 12% due to K fertilization. Fertilization with K tended to reduce the forage concentration of P, Ca, Mg, B, and Na. Application of K fertilizer to 0 K fertilizer plots at the conclusion of the experiment overcame any negative effects on DM yield due to prolonged absence of K fertilization. It was possible to achieve sufficiently low forage K concentrations for nonlactating dairy cow forage in all five cool-season grasses and maintain stand persistence, with lowest forage K concentrations in timothy.
Abbreviations: CP, crude protein • DM, dry matter • IVTD, in vitro true digestibility • NDF, neutral detergent fiber • OM, organic matter
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INTRODUCTION
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THE GOAL of a K management program for perennial cool-season grasses for nonlactating dairy cow forage is to provide optimum K for plant functions without accumulating excess plant K. Species selection, fertilization, harvest management, and time of season can all impact the K concentration of grass forage. Relatively low K concentration in nonlactating dairy cow diets is critical to animal health (Horst et al., 1997). Perennial grasses are luxury consumers of K, resulting in high K forages grown on fields with excess soil K due to repeated animal manure applications (Cherney et al., 1998).
Nitrogen fertilization can increase K concentration of grass forage if adequate soil K is available for uptake, but N fertilization of low soil K fields will result in decreased forage K concentration due to the dilution effects of high yields (Cherney et al., 1998). Reported critical K concentrations in grasses range from as low as 3 g kg–1 for some warm-season grasses (Gammon, 1952) to 25 to 27 g kg–1 for reed canarygrass (Allinson et al., 1992). Clearly, critical K values will vary within the same species, depending on harvest system and harvest management (Cherney et al., 1998).
Our objective was to determine if selection of grass species, along with appropriate fertilization and harvest management, will result in minimizing forage K concentration for nonlactating dairy cows while maintaining stand persistence.
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MATERIALS AND METHODS
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Timothy, orchardgrass, reed canarygrass, smooth brome, and tall fescue were established in 1996 on a Williamson silt loam (coarse-silty, mixed, active, mesic Typic Fragiudepts) soil with 0 to 6% slope in Ithaca, NY. This soil is classified as having medium K-supplying power, based primarily on their clay content.
Whole plots of grass species were split into three subplots (1.98 by 6.09 m) for K treatments. Treatments were (i) no K fertilization, (ii) 112 kg K ha–1 applied after spring harvest, and (iii) a split application of K with 56 kg K ha–1 applied after spring harvest and 56 kg K ha–1 applied after fall harvest (Table 1). The entire experimental area was fertilized at greenup each spring with 112 kg N ha–1, and 56 kg N ha–1 was applied following spring harvest. Broadleaf weed control was accomplished by annual applications of either 2,4-D [(2,4-dichlorophenoxy)acetic acid] at 0.14 kg a.i. ha–1 in the spring or dicamba (3,6-dichloro-2-methoxybenzoic acid) at 0.11 kg a.i. ha–1 in the fall.
A two-harvest-per-season management included an early- to mid-June (spring) harvest and an early- to mid-September (fall) harvest (Table 1). All five species reached the anthesis stage or later at spring harvest. A 1- by 5.8-m strip of each plot was harvested from each of four replicates for yield determination with a flail harvester at a 10-cm stubble height. Forage samples were oven-dried at 60°C for DM determination. Samples of approximately 800 g were collected for nutritive value analysis from the edge of the harvest strip at a 10-cm stubble height, dried at 60°C, and ground to pass a 1-mm screen.
Samples (0.5 g) were analyzed for neutral detergent fiber (NDF) using the procedure described by Van Soest et al. (1991) and ANKOM fiber analyzer with filter bags. In vitro digestibility was determined by incubating samples in buffered rumen fluid with urea for 48 h (Marten and Barnes, 1980) using the ANKOM incubator (Cherney et al., 1997). Digested sample residues were analyzed for NDF to determine in vitro true digestibility (IVTD). Digestibility of NDF was calculated as the proportion of the NDF digested after 48 h of incubation. The N concentration of samples was determined using a Leco N analyzer (LECO Corp., St. Joseph, MI) with Dumas combustion (Tate, 1994; Wiles et al., 1998).
Other plant elemental concentrations were determined by a dry ash method extraction using dilute HCl and elemental analysis using an inductively coupled emission plasma spectrophotometer (Greweling, 1976). Yield and recovery of K was calculated (Jokela, 1992). Yield of K was calculated as the product of forage DM yield and K concentration. Recovery of K applied was calculated as the quantity of K in the harvested forage minus the quantity in the 0 treatment, divided by the amount of K applied.
After fall harvest, soil samples were collected to a 152-mm depth, air dried, and manually crushed. Soil pH was measured from a 1:1 soil/water suspension (McLean, 1982). Soil organic matter (OM) was determined by loss on ignition at 500°C. Soil exchangeable K was extracted with 1 M ammonium acetate at pH 7.0 using a Zero Max E2 vacuum extractor (Zero Max, Minneapolis, MN) and analyzed by inductively coupled argon emission plasma, JY70 Type II (Instruments S.A., Edison, NJ).
Data were analyzed using the mixed model program of SAS (PROC MIXED) with repeated measures analysis (SAS Inst., 1997). Years were the repeated measures variable, and a heterogenous first-order autoregressive [ARH(1)] covariance structure was selected as the one that best fit the experimental data. Replicates and interactions including replicates were assumed to be random effects. Years were considered fixed effects, as years were sequential with potentially cumulative effects on soil and plant parameters. Grass species was the main plot, and K fertilizer was the subplot in this split-plot design. Multiple comparisons of all pairwise differences of least-squares means of fixed effects were adjusted using the Tukey–Kramer procedure in PROC MIXED. Standard errors for least-squares means calculated by PROC MIXED were adjusted for covariance parameter estimates (Littell et al., 1996). With heterogeneous covariance structures such as ARH(1) for repeated measures, standard error of the difference (SED) for years is different for each different pair of years. The SED values in data tables for years were obtained by pooling SED for different pairs of years and weighting them by their degrees of freedom. All significant differences mentioned in the following discussion are significant at P < 0.05.
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RESULTS AND DISCUSSION
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The species x year interaction was significant for every parameter evaluated while species x K fertilizer and K fertilizer x year interactions were rarely significant. Relatively large error degrees of freedom resulted in significant differences being detected due to some shifting in the relative order of treatments from year to year. There are no meaningful patterns to these interactions, and they are not presented or discussed.
Growing Conditions and Stand Persistence
Seasonal rainfall patterns were near normal in 2 yr, below normal in 2 yr, and above normal in 2 yr (Table 2). Harvesting these grasses at the anthesis stage or later in the spring, with only two harvests per season, minimizes any risk to stand persistence due to harvest management. Grass stands persisted relatively well throughout the study, with no visible differences among K treatments. Potassium deficiency symptoms were not visible on these grasses as observed in past experiments (Brown et al., 1969; Cherney et al., 2003). Reed canarygrass was beginning to encroach on other species, and some of the timothy and smooth bromegrass plots contained wild orchardgrass plants. Very early maturing wild orchardgrass routinely appears as a weed in plots of cool-season grasses in the Northeast. Other grass species generally consisted of less than 5% of the area for a given plot. Encroaching species were avoided for yield and quality sampling, eliminating the need for any covariate analysis.
Dry Matter Yield
Averaged over years, DM yield under split application of K fertilizer was significantly higher than the 0 K fertilizer treatment (Table 3). A single annual application of K fertilizer following spring harvest each year did not increase yields above that of the 0 K check. The proportion of the total seasonal yield in the spring was not influenced by K fertilization (Table 3) as it was for N fertilization (Cherney et al., 2003). While a split application of K fertilizer increased DM yield only 5.6% over the 0 K check, annual K uptake was increased 17.2%. Apparent K recovery was not influenced by timing of K application (Table 3). Apparent K recovery was low, agreeing with results from a previous study with reed canarygrass (Cherney et al., 2003).
There were no significant K fertilizer rate x grass species interactions. Averaged over years, timothy, reed canarygrass, and tall fescue produced significantly higher DM yields than orchardgrass or smooth bromegrass (Table 3). Yield was more equally distributed between spring and fall for tall fescue (55%) and reed canarygrass (56%) compared with 65 to 67% for the other species. Tall fescue had the largest annual K uptake and the largest apparent K recovery although not significantly different from orchardgrass or smooth bromegrass (Table 3). Reed canarygrass had the smallest K recovery due to relatively high K uptake under 0 K fertilization. This may be due to a deeper root system and/or more root mass than the other species. Soil K concentration in the 0 K treatment averaged 50.3 mg kg–1 in 1997 and tended to decline over years, dropping to as low as 24.9 mg kg–1 in 2001. Yields of DM and K were greatest and K recovery smallest during the first 2 yr of the study (Table 3). Quantity of K taken up by grasses in this study was relatively low compared with some studies (Allinson et al., 1992; Follett and Wilkinson, 1995). Proportion of yield in the spring from year to year is confounded with the date of spring harvest each year.
Soil Analyses
Soil test P was in the medium to high range for the entire experimental period. Soil test K increased significantly with annual application of K fertilizer (Table 4). Fertilization with K had no affect on soil OM but did lower soil pH from 6.7 to 6.6. Grass species did not influence any of the soil test parameters (Table 4). Soil test K tended to decline over years for all three K treatments. The year x K fertilizer interaction was significant for soil test K because all three K treatments were similar in 1997 while soil test K for the 0 K treatment was considerably smaller than the other treatments in succeeding years.
Forage Quality
For spring harvest, overall forage quality was not greatly impacted by K fertilization. Crude protein concentration under 0 K fertilization was greater than K-fertilized grass both in the spring and in the fall (Table 5). These statistically significant differences of 5 g kg–1 or less probably are not biologically significant from a forage quality standpoint. Forage quality of smooth bromegrass tended to be greater than the other species. Crude protein concentration of smooth bromegrass was greater than the other species in the spring, and IVTD and NDF digestibility (NDFD) were consistently high (Table 5). Timothy forage tends to be lower in crude protein (CP) than other cool-season grasses and was 27 g kg–1 lower than smooth bromegrass in the spring and 35 g kg–1 lower than orchardgrass in the fall. Reed canarygrass was low in CP, IVTD, and NDFD in the fall compared with most of the other species, and these values are consistent with previous reed canarygrass data (Cherney et al., 2003). Overall quality of spring growth from year to year generally reflected the timing of spring harvest (Table 5). Fall forage quality also appeared to be affected by spring harvest date—a late spring harvest resulted in improved fall forage quality. A late spring harvest in 2002 resulted in almost 50% higher NDFD in the fall forage compared with 2001.
As found in a previous study (Cherney et al., 2003), IVTD in perennial cool-season grasses was highly correlated with NDFD. The Pearson correlation coefficient was 0.963 (n = 360) for the spring harvest and 0.942 (n = 360) for the fall harvest. Using NDFD as the dependent variable, the slope of the regression line was slightly steeper in the fall compared with the spring (1.43 vs. 1.34). These IVTD vs. NDFD regression slopes for fall and spring forage are nearly identical to those from reed canarygrass fall vs. spring forage (1.42 vs. 1.34) (Cherney et al., 2003).
Elemental Composition
Potassium
Application of K fertilizer increased forage K concentration significantly over the 0 K fertilizer check (Table 6), but the increase was not great in either the spring or fall forage. Split application of K fertilizer with an application in the fall resulted in a very small yet significant increase in spring forage K concentration compared with a single application of K following spring harvest. Timothy was consistently lowest in forage K concentration although all five species were very low in K concentration in both the spring and fall (Table 6). Timothy DM yields were not greatly affected by low K concentration in the forage, disagreeing with results of Brown et al. (1969).
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Table 6. Concentrations of K, P, Ca, and Mg under two-harvest management as influenced by grass species and K fertilization.
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Results here agree with those from George et al. (1979), who reported no yield increase associated with K fertilization of smooth bromegrass on a prairie soil with low available soil K. According to Grant and MacLean (1966), timothy stands should persist over time with a forage K concentration of 15 to 18 g kg–1 in spring growth or 12 to 16 g kg–1 in regrowth. Stands persisted in this study with K concentrations in timothy regrowth as low as 8 g kg–1 although forage regrowth in our study was 3 to 4 mo old. Older plant tissue will eventually senesce, and K will be leached out of standing dead tissue. This process would lower the overall forage K concentration but would not necessarily have any negative impact on plant persistence. Potassium concentration in standing grass forage has been reported as low as 0.6 g kg–1 in buffalograss [Buchloe dactyloides (Nutt.) Engelm.] (Preston and Linsner, 1985). Concentration of K in the forage from year to year in our study varied primarily due to harvest date.
Phosphorus, Calcium, and Magnesium
In general, K fertilization reduced the concentration of P, Ca, and Mg in the forage (Table 6), whether split-applied or not. As with K, concentration of P, Ca, and Mg tended to be lowest in timothy compared with the other species. Tall fescue had the greatest Mg concentration in spring forage and has been found to be greater than other cool-season grass species in past studies (Cherney et al., 2002). Concentration of Ca tended to be smaller in the spring compared with the fall (3.51 vs. 5.68 g kg–1) over the 6 yr of the study, and the same pattern occurred in Mg (1.50 vs. 1.91 g kg–1). Concentration of P did not exhibit a consistent pattern from the spring to fall.
Manganese, Iron, Copper, Boron, Zinc, Molybdenum, Aluminum, and Sodium
Those interested in concentrations of elements considered essential to animal nutrition and those interested in establishing normal ranges for elemental concentrations in grasses for evaluation of the effects of soil amendments (McBride and Cherney, 2004) may find micronutrient concentrations of interest. Micronutrient concentrations in this study generally fell within the range of these elements in forage grasses according to Fleming (1973). Manganese concentration was greater in spring forage when some K fertilizer was applied in the fall compared with all application of K fertilizer after spring harvest (Table 7). This agrees with results from a reed canarygrass study (Cherney et al., 2004) where K fertilization increased Mn concentration in the spring but not in the fall. Boron and Na concentrations were decreased in both the spring and fall due to K fertilizer application (Tables 7 and 8). Zinc concentration was lower in the fall due to K fertilization but not in the spring. Potassium fertilization decreased Zn concentration in both the spring and fall forage in a previous study with reed canarygrass (Cherney et al., 2004).
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Table 7. Concentrations of Mn, Fe, Cu, and B under two-harvest management as influenced by grass species and K fertilization.
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Table 8. Concentrations of Zn, Mo, Al, and Na under two-harvest management as influenced by grass species and K fertilization.
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In general, timothy was low in most elemental concentrations compared with the other grass species, with the exceptions of Al and B (Tables 7 and 8). Elemental concentrations were relatively high for some species–element combinations including orchardgrass Mn and Mo, reed canarygrass Zn, and tall fescue Fe and Na. Most elemental concentrations tended to be higher in the fall than the spring, as large as a 75% increase in Mn. Copper, Zn, and Na concentrations were lower in the fall, as large as a 61% decrease in Na (Table 8). Elemental concentrations from year to year varied in part due to harvest date.
Effects of Uniform Potassium Fertilization in 2003
Following application of K fertilizer to the 0 K treatment plots in the fall of 2002 and a uniform application of K fertilizer to all plots in the spring of 2003, spring DM yield of the 0 K treatment was similar to both K fertilizer treatments (Table 9). Soil test K values for the 0 K fertilizer treatment remained lower than for K treatments, but this did not affect spring yields. Soil OM was similar for all three K treatments at the completion of the experiment. Soil pH for the 0 K treatment (6.4) remained higher than the K fertilizer treatments (6.3). Spring 2003 yield, soil OM, and soil pH were similar across all species (Table 9). At the conclusion of the experiment, soil test K was lowest in tall fescue plots, and tall fescue forage had the highest annual K uptake over the course of the experiment.
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Table 9. Soil test values and yield in spring 2003 following uniform K fertilizer application across treatments, as influenced by grass species and past K fertilizer application.
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SUMMARY AND CONCLUSIONS
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Potassium fertilization did not have a large effect on DM yield of cool-season perennial grasses under a low-intensity harvest management regime, and any negative effects on yield due to absence of K fertilization for 6 yr was overcome by fall plus spring K application on grass plots. Split application of K fertilizer after spring and fall harvests did increase DM yield and K uptake compared with the 0 K treatment. Potassium deficiency symptoms were not observed on any of the grass species although K concentration in fall-harvested forage dropped below 8 g kg–1 in timothy. Forage quality also was not greatly affected by K fertilization although it did affect forage K concentration and concentrations of some other elements. Timothy forage tended to be low in elemental concentrations in general, with lowest forage K concentrations among the five grass species. While the lower CP content in timothy makes it less desirable for lactating dairy cow forage, its low K content makes it an acceptable forage source for nonlactating cows. It was possible to achieve sufficiently low forage K concentrations for nonlactating dairy cow forage in all five cool-season grasses and maintain stand persistence.
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ACKNOWLEDGMENTS
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The authors thank Sam Beer and Leon Hatch for assistance with harvesting and analysis. This research was supported by the Cornell University Agricultural Experiment Station federal formula funds, Project no. 125451 and Project no. 127431 received from Cooperative State Research, Education, and Extension Service, USDA. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the authors and do not necessarily reflect the view of the USDA.
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NOTES
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Contribution from Cornell Univ. Agric. Exp. Stn.
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ABSTRACT
INTRODUCTION
