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Species and nitrogen effect on growth rate, tiller density, and botanical composition in grass hay production. (Forage & Grazing Lands).

ALTHOUGH INHERENT ABILITIES of cool-season grasses allow them to adjust their growth rates in response to abiotic factors, it is often reported that growth rates of cool-season grasses are greatest in the spring, followed by a lag during the summer, and recovery in the fall (Chamblee and Spooner, 1985). Abiotic factors alone do not control growth rates. Belesky and Fedders (1994) stated that weather, canopy tissue demography, nutrient availability, residual height after defoliation, developmental stage, and other management factors contribute to sward development rates.

Denison and Perry (1990) demonstrated that growth rates of orchardgrass and tall fescue (Festuca arundinacea Schreb.) were more variable in the third compared with the first week of regrowth. Stout and Jung (1992) reported that soil N, N fertilization, and temperature all influenced orchardgrass growth in the spring, while fall biomass accumulation was solely controlled by N fertilization.

Established grass swards develop new tillers or rhizomes through asexual reproduction from axillary buds (Waller et al., 1985). Tiller density oscillates as new tillers develop and existing tillers expire (Langer et al., 1964; Briske, 1991). Tillers in grass swards are also subject to size/density compensation, whereby fewer larger tillers develop under more lenient defoliation regimes (Bircham and Hidgson, 1983; Grant et al., 1983). Krause and Moser (1980) reported that smooth bromegrass tiller density was highest in early spring and decreased as spring growth progressed. Mitchell et al. (1998) concluded that smooth bromegrass tiller density was less predictable across years.

George et al. (1973) found that tiller density decreased 47, 32, and 52% during the summer following two harvest seasons in orchardgrass, smooth bromegrass, and timothy, when N application prior to each growth period was increased from 168 to 336 kg N [ha.sup.-1]. They went on to state that poor stand maintenance at higher levels of N resulted in fewer but larger plants having bare soil exposed between individual plants (George et al., 1973).

Loss of desirable plant species in a sward can create a niche for undesirable species. Lemieux et al. (1987) reported that the establishment period in timothy was dominated by annual broadleaf and grassy weeds, while weed populations in subsequent production years were composed mainly of perennial broadleaf weeds. Belesky and Fedders (1994) found that although broadleaf weeds were not present, other grasses represented [approximately equal to] 10% of the total herbage yield in a tall orchardgrass sward where a 50% defoliation treatment had been in place for the previous 3 yr.

Wardle et al. (1992) evaluated 10 pasture species and concluded that speed of emergence of musk thistle (Carduus nutans L.) and absolute emergence of bull thistle [Cirsium vulgare (Savi) Ten.] seedlings were significantly negatively correlated with pasture cover density, presumably as a consequence of alteration of light quality by the pasture swards. The objectives of this study were to determine the effect of grass species and N on growth rate, tiller density, and botanical composition responses in a hay production system.


A 2-yr field study was established in the fall of 1998 on a Quakertown silt loam (fine-loamy, mixed, mesic Typic Hapludults) at the Snyder Research and Extension Farm near Pittstown, NJ (40 [degrees] 30' N, 75 [degrees] 00' W). `Pennlate' orchardgrass, `Saratoga' smooth bromegrass, and `Chazy' timothy were seeded as main plots at 13, 13, and 11 kg seed [ha.sup.-1] with an oat (Arena sativa L.) cover crop (54 kg seed [ha.sup.-1]) on 11 September with a John Deere 8300 grain drill (1) (Deere and Company, Moline, IL) in 18 cm rows in 61 m by 17 m plots in a randomized complete block in a split-plot arrangement with four replications.

Prior to seeding, and in the spring after seeding, lime was applied to bring soil pH up to and maintain at 6.2. Phosphorus and K were added according to soil test recommendations to maintain available P and exchangeable K >81 and 311 kg [ha.sup.-1] Dicamba herbicide {3,6-dichloro-o-anisic acid} was applied at 0.28 kg a.i. [ha.sup.-1] in the spring of 1999 on all three species, and 0.56 kg a.i. [ha.sup.-1] on timothy and smooth bromegrass in the spring of 2000.

Subplots consisted of three N rates applied as ammonium nitrate, either the current recommendation of 112 kg [ha.sup.-1] in the spring at green-up followed by 56 kg [ha.sup.-1] after each harvest (low), or 2x (medium) and 3x (high) the recommendation. In 1999 and 2000, orchardgrass and smooth bromegrass received a total of 224, 448, and 672 kg N [ha.sup.-1], and timothy received 168, 336, and 504 kg N [ha.sup.-1] in both years. The N rates used in this study were part of a companion study to identify profitable and environmentally acceptable species x N rate combinations for the equine hay market and because equine are capable of tolerating 10 times the tissue nitrate concentration that is toxic to ruminants (Lewis, 1995).

First cut for all species was ideally planned for R0-R1 (Moore et al., 1991), but weather forecasts were considered before any harvests were initiated. Orchardgrass was harvested in mid-May, late June, and late August, while smooth bromegrass was harvested in late May, mid-July, and again in September each year. Timothy was harvested on June 7 in 1999 and on June 7 and August 24 in 2000. Cutting height was [approximately equal to] 6 cm for all species and harvests.

Growth cycles were defined as the spring growth period, after first harvest, after second harvest, and the fall growth period after third harvest. Mean growth rates were determined by clipping herbage weekly to [approximately equal to] 6 cm in four 0.25 [m.sup.-2] quadrats per subplot during the early phase of canopy development (20 to 30 d) in the first three growth cycles, while the entire length of the fall growth cycle (59 to 87 d) was used to calculate growth rates. Plot size was large enough to ensure that the same subplot area was not sampled twice for DM collection during a growth period. All herbage was dried in a forced-air oven at 50 [degrees] C to a constant weight for moisture determination. Tiller density was determined by counting all of the tillers in four 0.25 [m.sup.-2] quadrats per subplot [approximately equal to] 2 wk after each harvest. Although only one timothy harvest was made in 1999, tiller density was measured twice to quantify the effect of drought on tiller response. Botanical composition was determined after tiller density within the same quadrat by identifying all species. Tiller number was counted for all grass species, stem number for all legumes, and plant number for other species.

All data were analyzed using Proc Mixed procedures of SAS for a split-plot design in a randomized complete block (SAS Institute, 1996). The Bartlett test on the full model indicated that error terms for most data sets were not homogeneous, so a separate analysis is presented for each year. Species and N rate were considered fixed effects while block and block by species were considered random effects. All data were subjected to diagnostic analyses to confirm compliance with assumptions for ANOVA. Mean separation for main effects and interactions were obtained by Fisher's LSD, as described by Little and Hills (1978). Effects were considered significant in all statistical calculations if P-values were [less than or equal to] 0.1 to minimize the weighted average risk of Type I, II, and III errors (Carmer and Walker, 1988).


Growth Rate

Above-average temperatures throughout the 1999 growing season (Table 1), coupled with below-average precipitation, depressed growth rates during spring and summer (Table 2). In 1999, orchardgrass growth rate was not influenced by N, but an N rate x growth period interaction was observed because fertilizer burn at the high N level depressed orchardgrass growth during the second growth period, compared with the low N rate (3.41 vs. 4.65 g DM [m.sup.-2] [d.sup.-1]).

A 66, 59, and 53% reduction in growth rate in the low, medium, and high N rate, respectively, between the second and third growth cycle was mostly due to severe moisture stress when precipitation averaged 80% below normal. During the fall growth period, precipitation was plentiful and orchardgrass increased growth rate 63, 68, and 67% in the low, medium, and high N treatments, respectively, compared with the third growth cycle. Horst and Nelson (1979) observed compensatory growth of tall fescue in the fall following a period of summer drought stress. Compensatory growth in orchardgrass can alleviate forage shortfalls due to severe drought; however, fall growth in hay production systems is considered undesirable because dead material in first cut hay affects marketability.

Favorable environmental conditions in the spring of 2000 resulted in a 146% increase in growth rate compared with the spring of 1999 in orchardgrass. Similar to 1999, N did not affect growth rate, but a N rate x growth period interaction was observed because of a 32% lower growth rate at the mean medium and high N rate compared with the low during the second growth cycle. Apparently, even when adequate precipitation occurs, high levels of N can inhibit regrowth in orchardgrass. Conversely, the medium and high N rate had 52 and 53% higher growth rates in the fall compared with the low, presumably because of residual N that stimulated growth.

During the 2000 growing season, orchardgrass growth rate peaked during the spring growth period, which is similar to Denison and Perry (1990). Spring growth rates were greatest in smooth bromegrass in both years as well. Although N rate was not significant in 1999, growth period and a growth period x N rate interaction was observed in smooth bromegrass. The low N rate had the highest growth rate in the spring (2.36 g DM [m.sup.-2] [d.sup.-1]), followed by the lowest growth rate after first harvest (0.96 g DM [m.sup.-2] [d.sup.-1]). We observed reductions in growth rate ranging from 19 to 59% during a period of extreme drought, which is similar to the 30 to 60% reduction documented by Power (1971). Unlike orchardgrass, compensatory growth was not observed during the fall growth period in smooth bromegrass in 1999.

Smooth bromegrass growth period was highly significant in 2000. Similar growth rates were observed in both years at the low and medium N rate during spring growth, but growth rate was 16% higher in the high N treatment in 2000. No difference was detected among growth rates after first or second harvest. However, similarly to 1999, growth rates decreased during the fall growth period by 63, 56, and 43% in the low, medium, and high N rate, when compared with the third growth period.

During the 1999 growing season, timothy growth during the spring and fall growth periods were similar. Timothy growth was highly influenced by severe drought after first harvest, when growth rates decreased 81, 82, and 88% compared with the spring, before dormancy was initiated. In 2000, timothy growth rates decreased during each successive growth period because of a combination of reduced growth during periods with higher temperatures and the cumulative effect of stand reduction. Timothy growth rate in the fall of 2000 was only 13% of the growth rate during the fall of 1999, when averaged across N rate, because of a combination of stand reduction and probable compensatory growth that occurred following severe drought in 1999.

Tiller Density

Tiller density was generally unaffected by N rate during growth periods within species and year, except for orchardgrass in 2000, where the low N treatment had 56, 38, and 37% greater tillers [m.sup.-2] compared with the mean number of tillers at the medium and high N rate at the three sampling times. Apparently, as N rate increases, tiller density approaches a maximum, whereby yield increases beyond that point are largely due to increases in weight per tiller (Volenec and Nelson, 1995). Clearly, the low N rate in our study was at or close to the maximum tiller response to N because we observed yield responses to increasing N rates with similar or lower tiller densities (data not shown).

Temporal changes in tiller density in 1999 were significant in orchardgrass and smooth bromegrass (Fig. 1), which increased tiller density 54 and 106%, respectively, during the interval after first and second harvest, which may be explained by increased light penetration to the crown of the plant because of dry conditions and low growth rates that delayed canopy development. Normally, tiller expression may be suppressed during the spring in cool-season grasses because of culm development, while self-shading may influence tiller expression at other times (Belesky and Fedders, 1994).


A harvest interval of 42 and 55 d in orchardgrass and smooth bromegrass between first and second harvest also may have contributed to greater tiller density between the first and second sampling period. Auda et al. (1966) concluded that tillering increased as defoliation was relaxed because of carbohydrate buildup in stem bases where new tillers form. Tiller density declined significantly in orchardgrass after third harvest to 616 tillers [m.sup.-2], a 40% reduction, compared with 544 tillers [m.sup.-2] in smooth bromegrass, which only represented a 7% decrease. Mitchell et al. (1998) concluded that tiller demographics were highly variable by year in smooth bromegrass, which is consistent with the results from our study.

The dry conditions that prevailed until the second week of August in 1999 affected timothy tiller density the greatest. After first harvest, timothy had 576 tillers [m.sup.-2], intermediate between orchardgrass and smooth bromegrass. Nevertheless, within 8 d of the first sampling time, timothy tiller density decreased 10%.

During the 2000 growing season, tiller density decreased significantly from the sampling period after first harvest in all species. Orchardgrass tiller density declined 45% between the first and second sampling time, compared with 49% in smooth bromegrass. Unlike 1999, when timothy tiller density exceeded that of smooth bromegrass after first harvest, timothy tiller density at approximately the same Julian day was 36% lower in 2000. Furthermore, timothy tiller density, unlike orchardgrass and smooth bromegrass, continued to decline as the growing season progressed.

At the last sampling date in September of 2000, species and N rate were significant. Orchardgrass at the low N rate had 628 tillers [m.sup.-2], compared with 524 and 516 tillers [m.sup.-2] at the medium and high N rates. Similarly, in smooth bromegrass the low N rate had 352 tillers [m.sup.-2] compared with 320 and 276 tillers [m.sup.-2] in the medium and high N rates. Apparently, N had a cumulative effect on tiller density that required six harvests to manifest.

At all N rates, timothy tiller density declined the greatest of any species with 224 tillers [m.sup.-2] at the low N rate, compared with 104 and 156 tillers [m.sup.-2] at the medium and high N rates. George et al. (1973) observed a similar response to N on tiller density in timothy at a summer sampling period in the third production year.

Botanical Composition

For the duration of the study, growth rate and stand density contributed to weed encroachment among species. Species was significant for botanical composition after first harvest in the first production year (Table 3). Orchardgrass had 4.2 species 0.25 [m.sup.-2], compared with 7.2 and 1.5 species 0.25 [m.sup.-2] in smooth bromegrass and timothy in June of 1999, when averaged across N rate. Initially, greater botanical composition in orchardgrass and smooth bromegrass was most likely associated with competition during establishment coupled with dry conditions that reduced growth rates after first harvest in both species. Nitrogen rate also affected total composition after only two N applications in smooth bromegrass, where the high N rate had less diversity compared with the low N rate, which may partially be explained by a 35% higher growth rate in the high compared with the low N rate during the second growth period when botanical composition data were collected.

Although 10 species were found in orchardgrass in June of 1999 (Table 4), composition was dominated by Kentucky bluegrass (Poa pratensis L.) and yellow nutsedge (Cyperus esculentus L.), both of which responded to N rate. The low N rate had 33 tillers [m.sup.-2] of Kentucky bluegrass compared with 49 and 60 tillers [m.sup.-2] in the medium and high N rates. Similarly, the low N rate had 3 yellow nutsedge plants [m.sup.-2], compared with 6 and 37 plants [m.sup.-2] at the medium and high N rates. Clearly the depressed growth rates in orchardgrass at the medium and high N rates during this growth cycle contributed to greater densities of these two species.

Smooth bromegrass plots had the greatest diversity (11 species) in June of 1999. Six species were found in the greatest density, including timothy and Kentucky bluegrass. Unlike the orchardgrass sward, most species were not influenced by N rate. Averaged across N rate, other than smooth bromegrass, 79 timothy and 38 Kentucky bluegrass tillers [m.sup.-2] dominated perennial grass composition. The presence of annual grass was limited to smooth bromegrass, where downy brome (Bromus tectorum L.) was found at 11 tillers [m.sup.-2], when averaged across N rate.

Annual broadleaf species were more common and demonstrated a response to N. Smooth bromegrass had 17 plants [m.sup.-2] of mayweed chamomile (Anthemus cotula L.) in the low N treatment compared with 6 and 1 plants [m.sup.-2] at the medium and high N rates. Similarly, the low N rate had 4 plants [m.sup.-2] of common chickweed (Stellaria media (L.) Vill.) compared with 1.3 and 0.8 plants [m.sup.-2] at the medium and high N rates. Yellow nutsedge was present at 22 plants [m.sup.-2], when averaged across N rate. Aside from timothy, yellow nutsedge was the only other species present in the timothy sward, where it was found at 1.4 plants [m.sup.-2], when averaged across N rate.

In September of 2000, orchardgrass plots had 66% less diversity compared with an increase of 85% in timothy, from 2 to 13 species. Smooth bromegrass plots exhibited the greatest stability in species between the two sampling dates (11 vs. 12 species). Orchardgrass averaged 1.5 species 0.25 [m.sup.-2], compared with 3.5 and 5.7 species 0.25 [m.sup.-2] in smooth bromegrass and timothy. Similarly to 1999, smooth bromegrass at the low N rate had more total species compared with the high N rate, which may be partially explained by a 32% higher growth rate that resulted in faster canopy development. The opposite response was observed in timothy, where the high N rate had more total species than the low N rate, presumably due to lower tiller density as a result of stand loss.

Although tiller density decreased between June of 1999 and September 2000, the orchardgrass sward had six fewer species at the second sampling date. Aside from orchardgrass, yellow nutsedge was the only other dominant species, which was found at a density of 1 plant [m.sup.-2], when averaged across N rates. In spite of 12 species in the smooth bromegrass sward, yellow nutsedge was the only dominant species at 8.8 plants [m.sup.-2], when averaged across N rate.

The timothy sward not only had the greatest number of species in September of 2000, but also contained several species whose density increased as N rate increased. Among cool-season grasses other than timothy, smooth bromegrass (1.4 vs. 20.0 tillers [m.sup.-2]) and tall fescue densities (0.2 vs. 14.2 tillers [m.sup.-2]) increased markedly at the low compared with high N rate. Kentucky bluegrass densities did not respond as much as N rate increased (5.6, 3.9, and 8.1 tillers [m.sup.-2] at the low, medium, and high N rate, respectively). Yellow nutsedge densities increased 337% from the low to the high N rate (7.8, 17.5, and 26.2 plants [m.sup.-2]).

Nevertheless, many species were present in the different N treatments without responding to higher N levels. Among broadleaf annuals, hairy bittercress (Cardamine hirsuta L.) was found at all N levels at similar levels of 1.4 plants [m.sup.-2]. Redroot pigweed (Amaranthus retroflexus L.) and common lambsquarters (Chenopodium album L.) were not found at the low N rate, but had similar densities of 0.4 and 4.7 plants [m.sup.-2] in the medium and high N rates. Among perennials, white clover (Trifolium repens L.), sowthistle (Sonchus arvensis L.), and dandelion (Taraxacum officinale group) were found in all N rates at similar densities of 2.3 stems [m.sup.-2] and 5.1 and 0.4 plants [m.sup.-2]. Horsenettle (Solanum carolinense L.) was only found in the high N treatment, but densities were low at 0.5 plants [m.sup.-2].


Growth rates in orchardgrass were negatively affected by the medium and high N rate after first harvest in both years. Orchardgrass responded to changes in abiotic conditions by adjusting growth rate, while smooth bromegrass and timothy expressed less plasticity under favorable growth conditions. In a year with adequate precipitation, smooth bromegrass growth rates peaked in the spring, and then declined during two distinct growth phases in the summer and fall. Timothy growth rates rebounded during the fall of the first production year after a period of extreme drought, but this was not sustainable because of stand loss the following year.

All species exhibited temporal fluctuations in tiller density. Orchardgrass and smooth bromegrass tiller densities were not closely associated with yield, presumably because of compensation in tiller weight. Reductions in tiller density in timothy contributed to lower growth rates during the fall of 2000, when density dropped on average to 161 tillers [m.sup.-2]. Nitrogen did not affect tiller density during the first production year, but orchardgrass tiller density was negatively influenced by N throughout the second production year, including the fall growth period, when tiller density in all species was negatively affected.

Changes in botanical diversity were related to growth rate and tiller density. Initially, greater diversity in orchardgrass was most likely associated with competition during establishment. Nevertheless, subsequent aggressive growth rates in orchardgrass reduced botanical composition by 65% by the end of the second production year. Total diversity in smooth bromegrass plots decreased from 7.2 to 3.5 species 0.25 [m.sup.-2] from June of 1999 to September 2000, when averaged across N rates. Botanical diversity in timothy plots increased across time from 1.5 to 5.7 species 0.25 [m.sup.-2], when averaged across N rates, due to a combination of slow growth and lower tiller density as a result of stand loss. The high N treatment had 29% greater total species than the low N rate by the end of the second production year, comprised mostly of annual broadleaf, perennial grass, and other perennial species. Orchardgrass and smooth bromegrass are superior to timothy in Northeast hay production systems because of greater DM production and less weed competition.
Table 1. Mean monthly air temperature and precipitation
in 1999 and 2000 near Pittstown, NJ.

             Air temperature           Precipitation

Month   1999   2000     Normal     1999   2000   Normal

               [degrees] C                 mm

Mar.     3.7    6.1       3.7        74     79     96
Apr.    12.9    9.6       9.3        78     67    104
May     16.2   16.2      15.0        59    119    117
June    20.8   20.6      20.2        20     98    107
July    24.2   21.3      23.0        31     92    124
Aug.    22.3   20.8      22.2       118    130     99
Sept.   19.2   17.1      17.9       346    105     99

([dagger]) Normal data are average of previous 30-yr measured
at a weather station 11 km from experimental site.
Table 2. Growth rates of orchardgrass, smooth bromegrass, and
timothy at three N rates during different growth periods in
1999 and 2000 near Pittstown, NJ.

                                  N fertilization rate

                             Low           Medium        High

Species and
growth period            1999   2000   1999   2000   1999   2000

                          g DM ([dagger]) [m.sup.-2] [d.sup.-1]

  Spring                 3.27   8.60   3.27   7.96   3.30   7.66
  After first harvest    4.65   6.33   3.78   4.15   3.41   4.46
  After second harvest   1.60   6.95   1.54   5.21   1.60   4.45
  Fall                   4.29   1.59   4.85   3.31   4.83   3.35
  LSD (0.1) ([double                   1.51   0.94

  Spring                 2.36   8.71   1.65   8.18   1.83   9.14
  After first harvest    0.96   2.10   1.34   2.27   1.47   2.29
  After second harvest   1.22   1.83   1.34   1.53   1.44   1.71
  Fall                   0.70   0.67   0.67   0.67   0.75   0.98
  LSD (0.1)                            0.74   0.50

  Spring                 2.93   3.87   2.87   4.19   3.13   3.25
  After first harvest    0.57   1.01   0.51   1.34   0.39   1.21

  After second harvest
  Fall                   2.41   0.30   2.38   0.32   2.16   0.29
  LSD (0.1)                            1.07   0.38

([dagger]) DM = dry matter.

([double dagger]) LSD compares growth rate means among growth
periods at the same N rate and year.
Table 3. Least square means for total number of species x
life-cycle in orchardgrass, smooth bromegrass, and timothy
at two sampling dates at a low (L), medium (M), and high
(H) N rate near Pittstown, NJ.

                                   N fertilization rate

                     Orchardgrass       Bromegrass         Timothy

Life-cycle          L     M     H     L     M     H     L     M     H

                                     no. 0.25 [m.sup.-2]

                              June 1999

Annual grass       0.0   0.0   0.0   0.8   0.5   0.8   0.0   0.0   0.0
Annual broadleaf   0.3   0.3   0.0   2.8   2.3   1.3   0.0   0.0   0.0
Perennial grass    2.5   2.3   1.8   3.3   3.0   2.8   1.0   1.0   1.0
Perennial legume   1.0   0.5   0.8   0.0   0.0   0.0   0.0   0.0   0.0
Perennial          1.0   1.0   1.0   1.3   1.3   1.3   0.5   0.3   0.8
Total              4.8   4.1   3.6   8.2   7.1   6.2   1.5   1.3   1.8
LSD (0.1)                                  0.2
LSD (0.1)                                  1.2

                            September 2000

Annual grass       0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0
Annual broadleaf   0.0   0.0   0.0   1.0   0.8   0.5   0.3   1.8   1.3
Perennial grass    1.3   1.0   1.0   2.0   1.0   1     2.3   2.3   2.8
Perennial legume   0.0   0.0   0.0   0.5   0.5   0.0   0.8   0.5   0.5
Perennial          0.0   0.8   0.3   1.3   1.0   1.0   1.3   1.8   2.0
Total              1.3   1.8   1.3   4.8   3.3   2.5   4.7   5.9   6.6
LSD (0.1)                                  0.3
LSD (0.1)                                  1.7

([dagger]) LSD compares total species means.

([double dagger]) LSD compares total N rate means within species.
Table 4. Botanical composition of orchardgrass, smooth bromegrass,
and timothy by species at two sampling dates near Pittstown, NJ.

Orchardgrass              Smooth bromegrass             Timothy

                              June 1999

Cyperus esculentus L.   Anthemis cotula L.       Cyperus esculentus L.
Dactylis glomerata L.   Bromus inermis Leyss.    Phleum pratense L.
Festuca arundinacea     Bromus tectorum L.
Phleum pratense L.      Cyperus esculentus L.
Poa pratensis L.        Festuca arundinacea
Polygonum aviculare     Oxalis stricta L.
Stellaria media (L.)    Phleum pratense L.
Trifolium pratense L.   Poa pratensis L.
Trifolium repens L.     Sonchus arvensis L.
                        Stellaria media (L.)
                        Taraxacum officinale

                            September 2000

Bromus inermis Leyss.   Amaranthus retroflexus   Amaranthus retroflexus
                          L.                       L.
Cyperus esculentus L.   Bromus inermis Leyss.    Bromus inermis Leyss.
Dactylis glomerata L.   Cerastium vulgatum       Cardamine hirsuta L.
                        Cyperus esculentus L.    Chenopodium album L.
                        Euphorbia maculata L.    Cyperus esculentus L.
                        Festuca arundinacea      Festuca arundinacea
                          Schreb.                  Schreb.
                        Poa pratensis L.         Poa pratensis L.
                        Portulaca oleracea L.    Phleum pratense L.
                        Sonchus arvensis L.      Portulaca oleracea L.
                        Stellaria media (L.)     Solanum carolinense L.
                          Vill.                  Sonchus arvensis L.
                        Taraxacum officinale     Taraxacum officinale
                          group                    group
                        Trifolium repens L.      Trifolium repens L.

Abbreviations: DM, dry matter.

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Auda, H., R.E. Blaser, and R.H. Brown. 1966. Tillering and carbohydrate contents of orchardgrass as influenced by environmental factors. Crop Sci. 6:139-143.

Belesky, D.P., and J.M. Fedders. 1994. Defoliation effects on seasonal production and growth rate of cool-season grasses. Agron. J. 86: 38-45.

Bircham, J.S., and J. Hidgson. 1983. The influence of sward condition on rates of herbage growth and senescence in mixed swards under continuous stocking management. Grass Forage Sci. 38:323-331.

Briske, D.D. 1991. Developmental morphology and physiology of grasses, p. 85-1108. In R.K. Heitschmidt and J.W. Stuth (ed.) Grazing management: An ecological perspective. Timber Press, Portland, OR.

Carmer, S.G., and W.M. Walker. 1988. Significance from a statisticians viewpoint. J. Prod. Agric. 1:27-33.

Chamblee, D.S., and A.E. Spooner. 1985. Hay and pasture seeding for the humid south, p. 359-370. In M.E. Heath et al. (ed.) Forages: The science of grassland agriculture. 4th ed. Iowa State Univ. Press, Ames, IA.

Denison, R.F., and H.D. Perry. 1990. Seasonal growth rate patterns for orchardgrass and tall fescue on the Appalachian Plateau. Agron. J. 82:869-873.

George, J.R., C.L. Rhykerd, C.H. Noller, J.E. Dillon, and J.C. Burns. 1973. Effect of N fertilization on dry matter yield, total-N, N recovery, and nitrate-N concentration of three cool-season forage grass species. Agron. J. 65:211-216.

Grant, S.A., G.T. Barthram, L. Torvell, J. King, and H.K. Smith. 1983. Sward management, lamina turnover, and tiller population density in continuously stocked Lolium perenne-dominated swards. Grass Forage Sci. 38:333-344.

Horst, G.L., and C.J. Nelson. 1979. Compensatory growth of tall rescue following drought. Agron. J. 71:559-563.

Krause, J.W., and L.E. Moser. 1980. Tillering in irrigated smooth bromegrass (Bromus inermis Leyss.) as affected by elongated tiller removal, p. 189-191. In E. Wojahn and H. Thons (ed.) Proc. Int. Grassl. Congr., 13th, Leipzig, GDR. 18-27 May 1977. Akademie-Verlag, Berlin.

Langer, R.H.M., S.M. Ryle, and O.R. Jewiss. 1964. The changing plant and tiller populations of timothy and meadow fescue swards: I. Plant survival and the pattern of tillering. J. Appl. Ecol. 1:197-208.

Lemieux, C., A.K. Watson, and J.-M. Deschenes. 1987. Weed population dynamics in recently established timothy stands: Growth and physiognomy of the weed components. Can. J. Plant Sci. 67:1035-1044.

Lewis, L.D. 1995. Feeding and care of the horse. Williams and Wilkins, Baltimore.

Little, T.M., and F.J. Hills. 1978. Agricultural experimentation: Design and analysis. John Wiley and Sons, New York.

Mitchell, R.B., L.E. Moser, K.J. Moore, and D.D. Redfearn. 1998. Tiller demographics and leaf area index of four perennial pasture grasses. Agron. J. 90:47-53.

Moore, K.J., L.E. Moser, K.P. Vogel, S.S. Waller, B.E. Johnson, and J.F. Pedersen. 1991. Describing and quantifying growth stages of perennial forage grasses. Agron. J. 83:1073-1077.

Power, J.F. 1971. Evaluation of water and nitrogen stress on bromegrass growth. Agron. J. 63:726-728.

SAS Institute. 1996. SAS system for mixed models. SAS Inst., Cary,

Stout, W.L., and G.A. Jung. 1992. Influences of soil environment on biomass and nitrogen accumulation rates of orchardgrass. Agron. J. 84:1011-1019.

Volenec, J.J., and C.J. Nelson. 1995. Forage crop management: Application of emerging technologies, p. 3-20. In R.F. Barnes et al. (ed.) Forages: The science of grassland agriculture. 5th ed. Iowa State Univ. Press, Ames, IA.

Waller, S.S., L.E. Moser, and P.E. Reece. 1985. Understanding grass growth: The key to profitable livestock production. Trabon Printing Co., Kansas City, MO.

Wardle, D.A., K.S. Nicholson, and A. Rahman. 1992. Influence of pasture grass and legume swards on seeding emergence and growth of Carduus nutans L. and Cirsium vulgare L. Weed Res. 32:119-128.

Jeremy W. Singer *

Dep. of Plant Science, Cook College, Rutgers Univ., 59 Dudley Road, New Brunswick, NJ 08901-8520. Received 6 Mar. 2001. * Corresponding author (
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Author:Singer, Jeremy W.
Publication:Crop Science
Article Type:Statistical Data Included
Geographic Code:1USA
Date:Jan 1, 2002
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