Defoliation Management Research Articles

Response of a Georgia 5 tall fescue‐common bermudagrass mixture to season of nitrogen fertilization on the Coastal Plain

Georgia 5 tall fescue (Festuca arundinacea Schreb.) has the potential to grow in a mixture with warm‐season perennial grasses and provide a year‐round permanent pasture on the Coastal Plain. Season of fertilization with nitrogen (N) was evaluated as a determinant of yield and botanical composition on a Georgia 5 tall fescue‐common bermudagrass [Cynodon dactylon (L.) Pers.] stand on a slope extending from a dry Bowie sandy loam (Plinthic Paleudults) soil to a moist Beauregard sandy loam (Plinthaquic Paleudults) soil. Fertilization with 150 kg N ha−1 split into three applications in the cool season (November, January, and March) over three years resulted in greater tall fescue survival (77% basal cover) than an equal amount of N in the warm season (May, July, and September) or the two N treatments combined (42 and 52% tall fescue basal cover) by March 1998. Tall fescue yields were greatest in May. The harvest frequency of once every two months was perhaps too infrequent, thus allowing shade effects to combine with summer heat and drought stress to limit stand density and fall growth of tall fescue. Although invading plant species were affected by position on the slope and associated moisture conditions, neither stand density nor forage production of tall fescue was affected by location. Tall fescue stands were essentially eliminated by the atypically hot and dry conditions in the summer of 1998. Survival of this mixed Stand of cool‐season and warm‐season perennial grasses On this west Louisiana Coastal Plain site through several years prior to the 1998 drought indicates potential usefulness of such pasture mixtures. Stand density of tall fescue was enhanced by limiting fertilization with N to the cool season only. Defoliation management to optimize density of tall fescue stands in this environment needs further evaluation.

Nitrogen and Defoliation Management: Effects on Yield and Nutritive Value of Flaccidgrass

Abstract‘Carostan’ flaccidgrass (Pennisetum flaccidum Griseb.), a C4 perennial grass, has shown high quality potential in animal trials. Its yield response to defoliation frequency and N fertilization, however, has not been reported. We examined the influence of stubble height and of a range of N applications in two defoliation experiments over 4 yr. Experiment 1 (Raleigh, NC) combined two harvest heights, 76 and 38 cm, with two stubble heights, 25 and 15 cm (76–25, 76–15, 38–25, 38–15); all treatments received 380 kg N ha−1 yr−1. After Year 1, the 76–15 defoliation produced higher yields than 76–25 (Year 2: 11 330 vs. 7930 kg ha−1, P < 0.001; Year 3:8950 vs. 6270 g kg−1, P < 0.001), while in vitro dry matter disappearance (IVDMD) was similar (Year 3) (mean = 582 g kg−1). Compared with 38–15, the 38–8 defoliation resulted in lower yields (Year 2: 8638 vs. 9344 kg ha−1, P = 0.001; Year 3, 6173 vs. 8090 kg ha−1, P = 0.07) but higher IVDMD (Year 3, 651 vs. 635 g kg−1, P < 0.01). Experiment 2 (Raleigh, NC, and Watkinsville, GA) had four defoliations: clipping to 5 cm at 20 and 51 cm (vegetative) and to 8 cm at boot and anthesis stages (20–5, 51–5, Boot—8, Anthesis—8). All defoliation treatments were topdressed with 291 kg N ha−1, and 51–5 and Boot—8 were also evaluated with 179 and 403 kg N ha−1 (eight N—defoliation treatments in all). At both locations, highest yields were obtained with Anthesis—8, averaging 19 010 kg ha−1 at Raleigh and 12 390 kg ha−1 at Watkinsville. The 20–5 defoliation resulted in lowest yields at both locations, averaging 7648 kg ha−1 at Raleigh and 5100 kg ha−1 at Watkinsville. Defoliation frequency altered IVDMD (range = 550 to 789 g kg−1), but N application did not; however, increasing N application increased N concentrations linearly (P = 0.05). Flaccidgrass had high yield potential and high nutritive value at the Raleigh location, and warrants further evaluation in the upper South.

Nutritive Value of Clipped ‘Mott’ Elephantgrass Herbage

AbstractMany tropical grasses are low in nutritive value, but ‘Mott’ dwarf elephantgrass (Pennisetum purpureum Schumacher) has supported gains of yearling cattle (Bos taurus) approaching 1 kg d−1. To aid in identifying optimum harvest management practices for Mott, this study quantified crude protein (CP) and in vitro digestible organic matter (IVDOM) concentrations of leaf blade, leaf sheath, stem, and total herbage harvested following imposition of a wide range of clipping treatments. Treatments in 1989 and 1990 included all 16 combinations of four defoliation frequencies (3, 6, 9, and 12 wk) and four stubble heights (10, 22, 34, and 46 cm) in a randomized block design with three replicates. The soil was a hyperthermic, uncoated Aquic Quartzipsamment (Adamsville series). Data were analyzed by fitting multiple regression equations starting with a second‐order polynomial model. The range in IVDOM of total herbage harvested was from 653 to 791 g kg−1 (1989) and 680 to 739 g kg−1 (1990). Frequent defoliation to short stubble resulted in greatest IVDOM; herbage harvested infrequently to short stubble was least digestible. Total herbage CP ranged from 87 to 140 g kg−1 in 1989 and 89 to 133 g kg−1 in 1990, and was greatest with frequent harvest to a tall stubble. Mott elephantgrass CP and IVDOM were high across a wide range of defoliation frequencies and stubble heights. Because of Mott's high nutritive value even when defoliated infrequently (e.g., 9 wk), achieving yield and persistence goals can be the primary basis for selecting defoliation management practices.

Light Interception, Reserve Status, and Persistence of Clipped Mott Elephantgrass Swards

Defoliation management is an important determinant of persistence of perennial forages. Persistence and related responses of ‘Mott’ elephantgrass (Pennisetum purpureum Schum.) have not been studied under a wide range of defoliation management practices. The objective of this study was to determine the effect of defoliation frequency and stubble height on Mott canopy light interception, rhizome mass and reserve status at season end, tiller number in spring, and persistence. Treatments imposed in 1989 through 1991 included all 16 treatment combinations of four defoliation heights (10‐, 22‐, 34‐, and 46‐cm stubble) and four defoliation frequencies (3, 6, 9, and 12 wk). Treatments were replicated three times in a randomized block design, and the soil was a hyperthermic, uncoated Aquic Quartzipsamment. Data were analyzed by litting multiple regression equations starting with a second order polynomial model. Light interception after harvest ranged from 11 to 60% and was affected only by defoliation height. Light interception increased as defoliation height increased, but at a decreasing rate. Light interception before harvest ranged from 52 to 96% and was lowest for the 3‐wk defoliation frequency, 10‐cm stubble height treatment. In December following 2 yr of defoliation, rhizome total nonstructural carbohydrate concentration (TNC) ranged from 135 to 271 g kg−1 dry matter (DM), rhizome mass ranged from 24 to 733 g DM m−2, rhizome TNC content was from nearly 0 to 197 g TNC m−2, and rhizome N concentration was from 10.9 to 14.2 g kg−1 DM. Plants defoliated every 3 wk at a 10‐cm stubble height had the lowest rhizome mass, TNC concentration and content, and N concentration, while values were greatest for those defoliated every 12 wk at a 46‐cm defoliation height. Number of tillers per plant in May of 1990 and 1991 followed a similar trend. We conclude that Mott elephantgrass is persistent over a relatively wide range of clipping management practices, but close and frequent defoliation results in depletion of reserves and stand decline.

A review of the role of grazing management on the growth and performance of white clover cultivars in lowland New Zealand pastures

The current state of knowledge of white clover clonal growth processes and defoliation management is reviewed, and general recommendations on grazing principals made. Defoliation frequency determines herbage productivity through the manipulation of size/ density compensation between plant organ size (leaves) and numbers of growth units (growing point density). Hence large-leaved cultivars (Pitau, Kopu, Aran) are generally more productive under rotational grazing, whereas small-leaved cultivars are better suited to frequently grazed or set stocked conditions (Tahora, Prestige). The key to persistence is high growing point density, and the development of large-leaved densely branched cultivars should have superior performance over a wider range of grazing managements (Demand, Sustain). Grasses (perennial ryegrass, cocksfoot and tall fescue) grow by similar clonal processes to white clover and react in a similar manner to grazing management. Maintenance of pasture density (growing points/tillers) is crucial to persistence and is best achieved by rapid rotations or set stocking during spring/early summer. This provides protection against drought, and allows better exploitation of the genetic potential of species and cultivars through alternative grazing strategies over the remainder of the year. Keywords: clonal growth, cultivars, grazing management, morphology, populations, rotational grazing, seasonal growth patterns, set stocking, Trifolium repens L., white clover

Establishment of Rhizoma Perennial Peanut with Varied Rhizome Nitrogen and Carbohydrate Concentrations

AbstractRhizoma perennial peanut (RPP; Arachis glabrata Benth.) is a vegetatively propagated forage legume characterized by inconsistent establishment, possibly related to the chemical characteristics of RPP rhizomes used for propagation. This field study evaluated effects of chemical composition of ‘Florigraze’ rhizome planting material on emerged shoot number at 80 d after planting (DAP), rhizome and shoot mass accumulation at 180 DAP, percent RPP cover at season end, and herbage yield in June of the second growing season. The soil was a loamy, siliceous, hyperthermic Grossarenic Paleudult. Rhizome planting material was obtained from grazed pastures which, through varied defoliation management, produced rhizomes with a range of total nonstructural carbohydrate (TNC) (62‐383 g kg−1) and N (12.7‐25.8 g kg−1) concentrations. In 1990, a drought year, rhizomes with TNC ranging from 260 to 300 g kg−1 and N = 21 g kg−1 produced maximum responses for shoot number (39 m−2) and rhizome (530 kg ha−1) and shoot mass (1040 kg ha−1) accumulation. During the wetter than normal spring of 1991, rhizomes with TNC and N concentrations similar to those in 1990 supported 40 to 55% greater shoot counts and almost double (1050 kg ha−1) the rhizome mass accumulation. Because much RPP production occurs on nonirrigated sandy soils, and rainfall constraints are prevalent following planting in most years, assessment of rhizome planting material quality should be based on the 1990 results. In that year, rhizomes with TNC of 230 to 250 g kg−1 and N of 20 to 20.5 g kg−1 performed well, about 70 to 90% of the maximum responses indicated above. Rhizomes with TNC of 190 to 220 g kg−1 and N of 18 to 19 g kg−1 performed at about 40 to 65% of maximum responses. Planting rhizomes with TNC ≤ 180 g kg−1 and N ≤ 17 g kg−1 is not recommended unless irrigation is available, since establishment performance was ≤ 40% of maximum predicted responses.

Comparative Growth Analysis of Cool‐ and Warm‐Season Grasses in a Cool–Temperate Environment

Using both cool‐season (C3) and warm‐season (C4) species is a viable means of optimizing herbage productivity over varying climatic conditions in temperate environments. Despite well‐documented differences in water, N, and radiation use, no consistent evidence demonstrates productivity differences among C3 and C4 perennial grass species under identical management. A field study was conducted to determine relative growth rates (RGR), nitrogen productivity (NP), and mean radiation productivity (RP) (dry matter production as a function of incident radiation) of cool‐ and warm‐season grasses managed identically. Results were used to identify management practices that could lead to optimal productivity in combinations or mixtures of cool‐ and warm‐season grasses. Dry matter yields of warm‐season grasses equaled or surpassed those of cool‐season grasses, despite a 40% shorter growth interval. Certain cool‐ and warm‐season grasses appear to be suitable for use in mixtures, based on distribution of herbage production; however, actual compatibility may be altered by defoliation management. Relative growth rates varied among years and were about 40% lower for canopies clipped to a 10‐cm residue height each time 20‐cm of growth accumulated compared with other treatments. The RGR of warm‐season grasses was twice that of cool‐season grasses. Nitrogen productivity (g DM g−1 N d−1) and mean radiation productivity (g DM MJ−1) for warm‐season grasses was also more than twice that of cool‐season grasses. Radiation productivity of cool‐season grasses was dependent on N, while this was not always the case for warm‐season grasses. The superior production capability of certain warm‐season compared with cool‐season grasses in a cool–temperate environment can be sustained under a range of defoliation treatments and demonstrates suitability for use in frequently defoliated situations.

Defoliation Effects on Rhizoma Perennial Peanut Rhizome Characteristics and Establishments Performance

‘Florigraze’ rhizoma perennial peanut (RPP; Arachis glabrata Benth.) is a high‐quality forage legume vegetatively propagated by rhizomes. The impact of prior RPP defoliation management on rhizome chemical composition and growth after planting is not understood. These two studies, conducted on a Gressarenic Paleudult soil, evaluated the effects of grazing on (i) rhizome mass, total nonstructural carbohydrate (TNC), and N concentration, and (ii) rhizome establishment performance following planting. Rhizomes for both studies were obtained from pastures previously grazed at different combinations of rest interval length (d) and quantity of residual dry matter remaining after grazing (kg ha−1). Specific rest interval‐residual dry matter combiuatious (21‐500, 63‐500, 42‐1500, and 63‐2500) were chosen to represent a wide range of grazing severity. An ungrazed treatment (No‐Grz) was also included. Average rhizome mass was greatest (17.0 Mg ha−1) for No‐Grz and declined as grazing severity increased from 63‐2500 (9.4 Mg ha−1) to 21‐500 (2.3 Mg ha−1). Grazing treatments also provided rhizome planting material with a wide range of TNC concentration (62‐301 g kg−1) and N concentration (12.7‐22.1 g kg−1 Greatest concentrations were observed for No‐Grz and less severely grazed pastures. Planting rhizomes with initial TNC ≥ 228 g kg−1 and N ≥ 20 g kg−1 resulted in the greatest seasonal accumulation of both rhizome and shoot mass. Planting rhizomes with low TNC (62 kg−1; 21‐500) resulted in stand failure in a drought year (1990). Rhizomes with higher TNC (139 g kg−1; 63‐500) produced shoots that survived drought conditions but growth rates were relatively slow. We conclude that grazing affects chemical composition of RPP rhizomes and that chemical composition of planting material is a major determinant of RPP establishment success.

The Establishment and Maintenance of a Species‐Rich Grassland on a Reclaimed Opencast Coal Site

AbstractWe conducted an experiment with the dual aims of (1) examining the feasibility of establishing a species‐rich grassland using a commercially available grass and wild‐flower seed mixture and (2) examining the effects of different defoliation and fertilizer managements on the productivity, species richness, diversity, and composition of a species‐rich grassland established on a site reclaimed after opencast coal mining. The use of the seed mixture successfully established a sward of some 18–25 species per square meter. The species composition was enriched to some extent by recruitment of unsown species, principally from the soil seed bank. Hay‐type defoliation management produced greater dry matter yield and species richness than grazing defoliation, but grazing defoliation produced greater species diversity. Fertilizer application had no significant effect on dry matter production but reduced species diversity. Ordination analysis revealed that both defoliation and fertilizer management significantly affected species composition. The response obtained by individual species was explicable largely by their comparative biology.

Management and productivity of white clover in a kikuyu grass sward in subtropical Australia

This plot-cut study, on heavy clay soil, evaluated the establishment, productivity and persistence of Haifa white clover (Trifolium repens) in a vigorous sward of kikuyu grass (Pennisetum clandestinum). Defoliation treatments were 5 or 12 cm stubble height in spring and 14 days or "when ready" (lower leaves beginning to senesce) in spring and autumn. Over the 2t/2 years of the study and under optimal defoliation treatment (5 cm stubble height in spring and at the "when ready" defoliation interval in spring and autumn), total yield of forage was 19 952 kg DMfha/yr, of which 57% was white clover. The reason for the loss of vigour of white clover in year 3 is not clear. It may have been due to the heavy infestation of the root knot nematode Meloidogyne or to defoliation management over the second summer, or both. Management at the transition phases between the two pastures (early autumn and late spring) is critical to success and is explained in the light of farmer experience. Keywords: defoliation management, Pennisetum clandestinum, subtropics, Trifolium repens

Defoliation Effects and Seed Yield Components in Pearl Millet ✕ Elephantgrass Hybrids

AbstractPrior to widespread use of seeded hybrids of pearl millet ✕ elephantgrass [Pennisetum glaucum (L.) R. Br. ✕ Pennisetum purpureum Schumach.], management to permit mechanical seed harvesting must be developed. Extreme panicle height and high biomass complicate this procedure. Defoliation management is a potential solution. This field study was conducted on a Mulat sand (sandy, siliceous, thermic Arenic Ochraquults) to (i) evaluate the effects of three defoliation treatments on height of panicles, days to flowering, seed yield components, seed yield, seed germination, and plant survival in four hybrid genotypes and (ii) evaluate the associations among seed yield components under these defoliation treatments through the use of path‐coefficient analysis. In the defoliation treatments, plants were cut zero, two, and three times per year at a 30‐cm stubble height, both in 1991 and 1992. Linear effects of defoliation accounted for 18 to 90% (1991) or 18 to 96% (1992) of the total variation in the characteristics studied. Genotype ✕ treatment ✕ year interactions were common. Panicle height and plant biomass were drastically reduced with two and three cuts per year. Defoliation delayed flowering. Two cuts per year (mid‐June and early August) did not decrease seed yield and seed quality significantly, nor did they affect plant survival Three cuts per year (the last in mid‐September) drastically reduced seed production and seed quality. Path‐coefficient analyses gave significant defoliation treatment and year effects in all traits. Seeds per panicle was always highly correlated to seed yield per plant, due to high positive direct effects and relatively low indirect effects through the other components. Defoliation altered the correlational structure among seed yield components and the compensatory mechanisms among them, but adequate seed production was maintained with two cuts per year.

Cutting Height and Frequency Effects on Composition, Yield, and Quality of a Bermudagrass-Crabgrass Mixture

‘Coastal’ bermudagrass [Cynodon dactylon (L.) Pers.] is the most abundant warm-season perennial grass in the lower South. Large crabgrass [Digitaria sanguinalis (L.) Scop.] will often invade stands of Coastal bermudagrass but little is known about the response of this species mixture to defoliation management. A study was conducted in 1990 and 1991 to determine the effects that cutting height and interval have on species composition, dry matter (DM) yield and quality of a bermudagrass-crabgrass mixture. Percentage crabgrass, DM yield, crude protein (CP) and in vitro organic matter digestibility (IVOMD) were measured on small plots of coastal bermudagrass that were cut at three cutting heights (1, 4, and 7 in.) and five cutting intervals (1, 2, 3, 4, and 6 wk). Percentage crabgrass was low in 1990 and did not show a response to cutting height. Higher crab-grass percentages in 1991 showed a positive linear response to cutting height and a negative linear response to cutting interval at both the middle and end of the experiment. There was a linear decrease in DM yield as cutting height increased, but yield increased linearly with increased cutting interval. Crude protein percentage declined linearly with increased cutting interval, but a linear response to cutting height in both years changed from negative to positive as interval increased. There was a curvilinear increase of IVOMD as cutting height increased in both years. In 1990, there was a linear decrease of IVOMD as interval increased with the rate of decrease being higher as cutting height increased; however, in 1991, there was a curvilinear decrease of IVOMD with increasing interval. Results of this study indicate that cutting height and frequency interact to affect the productivity, quality, and composition of bermudagrass-crab-grass mixtures. Research Question ‘Coastal’ bermudagrass is extensively used in the lower South for both grazing and hay. Bermudagrass yield and nutritive value can be high; however, these attributes are greatly influenced by both cutting height and frequency. Crabgrass encroachment can further affect bermudagrass yield and quality. The objective of this study was to determine the effects of cutting height and interval on yield, quality, and botanical composition of a Coastal bermudagrass-crabgrass mixture. Literature Summary Several studies with Coastal bermudagrass have shown that reducing the frequency of harvests increases dry matter yield at the expense of forage quality. Other research has shown declines in yield and increases in quality as the cutting height increases. These studies, however, did not look at the combined effects of cutting height and frequency on yield and quality. Study Description A plot study was conducted in 1990 and 1991 with an existing stand Coastal bermudagrass. Location: East central Alabama Soil: Marvyn loamy sand (fine-loamy, siliceous, thermic, typic haplodult) Fertilization: N—150 lb/acre at start and midpoint P—44 lb/acre at start K—150 lb/acre at start and midpoint Irrigation: Applied weekly if necessary to provide 1 in./wk Cutting heights: 1, 4, and 7 in. Cutting frequencies: 1, 2, 3, 4, and 6 wk. Applied Questions How do bermudagrass-crabgrass mixtures respond to cutting height and frequency? In this study, the highest dry matter yields were obtained with a 6-wk cutting interval and 1-in. cutting height. Unfortunately, this treatment combination also resulted in the lowest crude protein and dry matter digestibilities. The highest quality forage was harvested at 1-wk intervals, with crude protein and in vitro organic matter digestibility tending to be higher for the 7-in. height at each interval. Thus, an alternative for improving the quality of bermudagrass hay could be to raise the cutting height. Trends in the yield and quality data indicate benefits in quality if heights are increased to 4 in. However, increases in quality with heights taller than 4-in. do not appear to be enough to offset the decline in yield. Can clipping management affect the botanical composition of a bermudagrass-crabgrass mixture? The two grasses responded differently to the cutting treatments. Crabgrass was most competitive with bermudagrass when the mixture was harvested frequently with a tall cutting height. Thus, cutting 1 in. above the soil surface at 4- to 6-wk intervals appears to provide bermudagrass with a competitive advantage.

Impact of Grazing Management on Soil Nitrogen, Phosphorus, Potassium, and Sulfur Distribution.

Little information is available directly comparing soil nutrient distribution under different defoliation managements. During 1990 (116 d) and 1991 (141 d), 'Callie' bermudagrass (Cynodon dactylon var. aridus Harlan et de Wet) pastures grazed by Holstein heifers (Bos taurus) were used to determine the effects of two rotational stocking methods and continuous stocking on lateral and vertical distribution of extractable N, P, K, and S. A hay management also was included to compare soil responses under grazing and clipping. Nutrient distribution and concentration in the Ap1 horizon (0- to 15-cm soil depth) did not differ among grazing methods, but N, P, and K accumulated in the third of the pastures closest to shade, water sources, and supplement feeders (lounging areas where cattle tend to congregate or rest). Similar observations were made with K in the Ap2 horizon (15- to 30-cm soil depth). Nutrient concentrations were lower or tended to be lower in the Ap1 horizon of the hay management than in grazed pastures because of nutrient removal in harvested herbage. Across defoliation managements, greater extractable N, P, and K concentrations were observed in the Ap1 horizon in 1991 than in 1990. For N and K, this was attributed to fertilizer inputs in all managements and partially to supplemental feed inputs in grazed pastures. Increases in extractable P appeared to be associated primarily with flooding of the experimental site in late 1991. This study suggests that grazing method of well-managed pastures may have little effect on short-term (2 yr) soil nutrient distribution, especially when grazing occurs during months when temperatures are high.

Management of Lolium perenne/Trifolium repens pastures in the subtropics. II. Effect of summer defoliation, irrigation duration, seedbed preparation and pasture type

This study on the north coast of New South Wales, Australia, evaluated the effect of irrigation and defoliation management over summer, pasture type and seedbed preparation on production and survival of a perennial ryegrass pasture over an 18-month period from sowing. In a relatively dry summer, irrigation sufficient only to keep plants growing, increased production of ryegrass plus clover from 2826 to 5515 and 3210 to 5396 kg DM/ha in summer and the subsequent autumn/winter, respectively, and increased survival of ryegrass plants by 34%. The more summer active Olwen white clover/NZA895 perennial ryegrass combination had a 16% higher production in summer, but a 11% lower production in winter than a Haifa/Yatsyn sward. The difference in production was entirely due to the clover component of the pasture. DM yield in the first growing season for the ryegrass/white clover pasture was equivalent to applying 20 kg N/ha/month to a pure ryegrass sward. In the subsequent summer/autumn/winter, the yield of pure ryegrass pasture was well below the ryegrass/white clover swards at any rate of N application. There was no difference between survival of NZA895 and Yatsyn ryegrass or incursion of summer grass into their respective plots. Plots defoliated over summer at 6 cm, as opposed to 12 cm, stubble height yielded 54% more edible DM and resulted in a 65% higher ryegrass plant survival rate. There was no effect on summer grass incursion. Multiple cultivations appear to be the key to appropriate seedbed preparation, with this treatment achieving the highest ryegrass survival rate, lowest summer grass incursion and highest DM yields.

Effects of defoliation management on the productivity of an irrigated Persian clover sward

A field experiment investigated the effects of frequency and height of defoliation on the productivity of an irrigated Persian clover (Trifolium resupinatum) sward. Combinations of 4 intervals of harvest (3, 6, 9, 12 weeks) and 2 heights of defoliation (to ground level or 5 cm above ground level) were used in a randomised block experiment, with 2 additional treatments of 4 and 18 weeks between harvests defoliated to ground level. Total herbage accumulation ranged from 8.46 to 13.90 t DM/ha and varied according to defoliation management. Except for the very short defoliation intervals, harvesting to 5 cm was less productive than harvesting to ground level. The effects of leaf area index, herbage yield, and infection with leaf fungal disease on growth rates were assessed. Leaf area had a positive effect, and fungal disease a negative effect, on herbage growth rates, while maximum growth rates in autumn-winter were achieved when herbage yield reached about 2.0 t DM/ha. Dead matter accumulation increased with the interval between harvests, and weeds invaded the plots at both the shortest and longest defoliation intervals. The quality of seed produced (seed weight) was not influenced by defoliation treatment (0.1112 g/100 seeds, on average). Defoliation interval was positively related to number of inflorescences and quantity of seed set, but height of defoliation did not significantly affect these variables. It was concluded that the optimum interval of harvest was 6-9 weeks. Height of defoliation had only minor effects, due to the small difference in residual dry matter between the treatments.

Influence of defoliation on some aspects of regrowth and senescence of Persian clover herbage grown in pots

This experiment investigated the effects of defoliation management of Persian clover (Trifolium resupinatum) on herbage production, and in particular, regrowth and losses of production due to senescence. Three heights of defoliation of Persian clover (0, 5, 10 cm above soil level) were superimposed on 3 frequencies of defoliation (4, 6, 12 weeks between harvests until early October; 3, 4.5, 9 weeks subsequently) in a completely randomised pot experiment with 3 replicates. Defoliation management had a large effect on yield of harvested herbage, in agreement with earlier studies with Persian clover in mixed swards or as a monoculture in the field. The amount of herbage that grew below defoliation height and subsequently died was 0-21% of the total herbage grown. The amount of dead and dying matter in herbage above and below defoliation height increased as both defoliation height and interval increased. This represented up to 61% of the total herbage grown. Aspects of regrowth (leaf area, petiole number, petiole extension rate, yield of herbage during growth, biomass of root relative to shoot) were measured. Except at very long defoliation intervals, vegetative growth of Persian clover herbage was positively associated with all of the above variables. The pattern of change with time in the rate of green herbage accumulation following defoliation reflected the balance between changes in the growth of new plant tissue and the loss of mature tissue to senescence and decomposition.

Spring defoliation of white clover seed crops. 2. Potential harvestable seed yield and seed yield components of contrasting white clover cultivars

AbstractThe effects of different spring defoliation managements on potential harvestable seed yield and seed yield components of three contrasting white clover cultivars were assessed. The small‐leaved cv. S184 produced more but smaller inflorescences than the large‐leaved cv. Olwen and Menna, a medium‐leaved cultivar. Cultivar Olwen, however, produced more ripe and brown (nearly ripe) inflorescences with more florets, seeds per floret and a higher seed yield per ten inflorescences than the other cultivars. Potential harvestable seed yield and individual seed yield components were only influenced by defoliation after bud emergence, as defoliation before bud emergence had no effect on seed yield components. Defoliation after bud emergence had a similar effect on all cultivars: the number of ripe inflorescences was unaffected by defoliation but the number of brown and therefore harvestable (ripe + brown) inflorescences was highest following defoliation three weeks after bud emergence. Florets per inflorescence, seed per floret, 1000 seed weight, seed yield per ten inflorescences and potential harvestable seed yield were not influenced by defoliation after bud emergence. Season had a significant effect on seed yield components and influenced the effect of defoliation treatments, emphasizing the importance of climate in white clover seed production. The results are discussed in relation to the spring defoliation of white clover seed crops, harvesting techniques and the provision of guidelines for optimizing seed yield.

Effects of frequency and height of defoliation on the production of a Persian clover-annual ryegrass sward

An experiment established the effects of frequency and height of defoliation on the production of an irrigated Persian clover (Trifolium resupinatum)- annual ryegrass (Lolium rigidum) sward. Five intervals of defoliation (from 4 to 12 weeks) were superimposed on 2 heights of defoliation (to ground level and to 4 cm above ground level) in a split-plot design. Total harvested yields ranged from 7.52 to 11.94 t DM/ha and varied according to defoliation management. Except for the very short defoliation intervals, defoliating to the higher level was less productive than defoliating to ground level. There were wide seasonal variations in the effect of treatment. In general, quality of the harvested herbage was relatively constant for much of the year, but in spring the effects of frequency and height of defoliation were evident. At this time, all chemical characteristics indicated that herbage quality declined with maturity of the sward. Optimum defoliation management will depend on both the quantity and quality of herbage produced. This will depend on animal requirements.

Productivity and Quality of Bermudagrass in a Cool Temperate Environment

AbstractIn temperate environments a warm‐season species is needed to provide forage during summer when the growth rate of cool‐season forages is low. Management data for warm‐season pasture is limited for the Appalachian region. A bermudagrass [Cynodon dactylon (L.) Pers.] selection RS1, has been identified which is capable of growth and persistence in areas where other cultivars of the species winterkill. A field study was conducted to determine RS1 bermudagrass productivity and quality as affected by a split application of 60, 120, 240, or 360 kg N ha−1 and a 2‐, 4‐, or 6‐wk delay of initial harvest on a fine‐loamy, mixed, mesic, Typic Hapludult (Gilpin) soil. Treatments were replicated four times in the field, and the study was conducted for 2 yr. Delaying initial harvest significantly increased yield in both years to more than 8 Mg ha−1 when 360 kg N ha−1 yr−1 was applied. Herbage yields typically ranged between 3 and 6 Mg ha−1 and would contribute substantially to forage requirements in mid‐summer in the region. Increased N resulted in higher herbage yield regardless of harvest delay regime. Herbage yields were about 25% less in 1989 than in 1988 and could be due in part to cool and wet conditions in 1989, compared to a hot, dry 1988 growing season. Bermudagrass in vitro dry matter digestibility and crude protein declined with delayed initial harvest (maturity), increased following the mid‐season N application, and continued to decline into late summer. Season average quality was not affected by initial harvest delay. Bermudagrass (RS1) will persist and respond to N fertilizer and defoliation management in cool, temperate environments and promises to be a useful component in forage‐based animal production systems in the region

Integrated pest management of forest defoliators in the southeastern United States

A multitude of defoliating insect species occur in the temperate and sub-tropical forests of the southeastern U.S. Two groups, however, stand out as persistent, annual problems that demand the attention of forest pest managers. These are the tent caterpillars (Lepidoptera: Lasiocampidae) and the pine sawflies (Hymenoptera: Diprionidae). Pest-management tactics developed to date have involved population dynamics and modeling as well as biological and cultural controls. Sampling schemes using pheromone-baited traps provide an indication of relative population density for several important defoliator species. The use of traditional chemical controls has been inhibited by the diversity of forest fauna, economics, and environmental sensitivity. New pest problems are emerging and are a major focus of research efforts. This has been a result of shifts in resource usage as well as tree stress and subsequent predisposition to previously unimportant pest species.