Herbage production and persistence of two tropical perennial grasses and forage sorghum under different nitrogen fertilization and defoliation regimes in a summer‐dominant rainfall environment,Australia

An experiment was conducted in inland northern New South Wales (NSW) to assess the response of tropical perennial grasses Chloris gayana (Rhodes grass) cv. Katambora and Digitaria eriantha (digit grass) cv. Premier and annual forage sorghum (Sorghum bicolor ssp. bicolor × S. bicolor ssp. drummondii hybrid) cv. Sweet Jumbo fertilized with five rates of nitrogen (N; 0, 50, 100, 150 and 300 kg N ha^?1) and defoliated every 2 or 6 weeks over two growing seasons. Tropical perennial grasses were highly responsive to N fertilizer, while there was no significant response by forage sorghum. Herbage production of Rhodes grass increased linearly whereas digit grass had a high response at 50–100 kg N ha^?1. Nitrogen‐use efficiency was highest during the growing season when rainfall was higher. During this season, digit grass had the highest N efficiency (148 kg DM kg^?1 N applied) at 50 kg N ha^?1, and Rhodes grass (66 kg DM kg^?1 N applied) at 100 kg N ha^?1. Plant frequency of both perennial species increased and then stabilized at high levels (>84%, cell size 0·1 by 0·1 m) during the two growing seasons. Plant frequency of Rhodes grass declined over the winter period, but recovered within 6 weeks of commencement of the growing season. Soil nitrate levels indicated that unused nitrate moved down the soil profile during wet winters. Implications of leaching below the rooting zone are discussed.     

Soil water dynamics,herbage production and water use efficiency of three tropical grasses: Implications for use in a variable summer‐dominant rainfall environment,Australia

In the moist mid‐latitudes of eastern Australia, soil water dynamics, herbage production and water use efficiency (WUE) were monitored during 2006–2008, for five perennial pastures: digit grass (Digitaria eriantha), Rhodes grass (Chloris gayana), forest bluegrass (Bothriochloa bladhii), native grass (Bothriochloa macra and Rytidosperma bipartita dominant), lucerne (Medicago sativa); and two forage crops: oat (Avena fatua) and sorghum (Sorghum bicolor). Ground cover formed more quickly in Rhodes grass and lucerne (>70% ground cover in 120 and 175 days after sowing [DAS] respectively) than in forest bluegrass and digit grass (245 and 365 DAS respectively). Values of maximum extractable water (MEW) for Rhodes grass and lucerne were similar (180–242 mm), while values for digit grass and forest bluegrass (129–175 mm) were equal to or greater than those for native grass, and two annual forage crops (77–144 mm). Lucerne expressed the maximum root depth (1.46 m), while values for the tropical grasses (0.96–1.39 m) were greater than native grasses and forage crops (0.87–0.96 m). Native grasses (6.5–12 t DM/ha) had the lowest herbage production, which resulted in values of WUE that were significantly less than most other treatments (16–21 vs. 23–43 kg DM ha^?1 mm^?1). Digit grass (33–34 kg DM ha^?1 mm^?1) had higher WUE compared with the other tropical grasses (20–27 kg DM ha^?1 mm^?1). The data collected here suggest that a forage system comprising digit grass, lucerne and forage oat would provide high production and WUE in this environment.     

SPRING AND SUMMER ROOT GROWTH OF SOME TEMPERATE–REGION GRASSES AND SUMMER ROOT GROWTH OF TROPICAL GRASSES

The root growth of 3 temperate–region grasses (perennial ryegrass, Italian ryegrass, and cocksfoot) and of 3 tropical grasses (Dallis grass, Bahia grass, and Rhodes grass) was investigated in large glass–sided root–boxes. The trend of root numbers and the rate of elongation of roots were ascertained to discover how the Japanese climate affected the root growth of these species.
All the temperate–region grasses produced new roots vigorously during spring, but root growth ceased in August, whereas the roots of tropical grasses grew rapidly in this month. The alternate use of these two types of grasses during the growing season may therefore be worthwhile in Japan     

Characterization for industrial purposes of the fibre anatomy of perennial ryegrass and tall fescue stem and leaf at three stages in the primary growth

Characterization of grass fibre is important in assessing its potential for industrial fibre applications. Stem and leaf sections were sampled from triplicate field plots of two grass species, perennial ryegrass (PRG) and tall fescue at three dates (monthly from 12 May) in the primary growth, and were used to (a) isolate individual fibre cells and (b) prepare transverse sections. Microscopy and image analysis software were used to determine the length and width of individual fibre cells and the proportion of lignified fibre in stem and leaf transverse sections. The length and width of individual fibre cells were greater (P < 0·001) in stem than in leaf sections, while individual fibre cell length was greater (P < 0·01) for tall fescue than PRG. Harvest date and grass species had little effect (P > 0·05) on the proportion of lignified fibre in the transverse‐sectional area. However, there was a greater (P < 0·001) proportion of lignified fibre in the transverse‐sectional area of grass stems than leaves, with tall fescue having a greater (P < 0·05) stem and leaf transverse‐sectional area and area of lignified fibre in transverse section than PRG. Tall fescue harvested at a later stage of growth, with higher proportions of stem than leaf tissue, may be more suitable for industrial fibre applications.     

Adaptability and productivity of some warm-season pasture species in a Mediterranean environment

Warm‐season grasses and legumes have the potential to provide forage throughout the Mediterranean summer when there are high temperatures and low rainfall and when cool‐season grasses become less productive. Twenty‐nine non‐native, warm‐season pasture species (twenty‐three grasses and six legumes) were assessed for their adaptability to the coastal plain of southern Italy in terms of their productivity and nutritional quality. The investigated species were compared with two reference species widely used in a Mediterranean environment: a grass (Festuca arundinacea) and a legume (Medicago sativa). The species differed in their phenological and biological characteristics, i.e. start of vegetative resumption, first flowering and cold resistance, from each other and from the control species. From the second year after establishment, warm‐season perennial grasses had high dry‐matter (DM) yields and, in many cases, a more than adequate nutritional quality. As for legumes, the control, M. sativa gave the best results in all the investigated characters. Among the grasses, seven species (Chloris gayana, Eragrostis curvula, Panicum coloratum, Paspalum dilatatum, Pennisetum clandestinum, Sorghum almum, Sorghum spp. hybrid) had DM yields greater than the control species and had their maximum growth during the hottest period of the year, when F. arundinacea, the control grass species, was dormant. Eragrostis curvula had the highest annual DM yield (21·1 t ha^?1) and P. clandestinum provided the best combination of agronomic and yield characteristics which were similar to those of M. sativa. The seven above‐mentioned species have the potential to supply hay or grazing and contribute to broadening and stabilizing the forage production calendar in Mediterranean‐type environments.     

Impact of deferred grazing and fertilizer on plant population density,ground cover and soil moisture of native pastures in steep hill country of southern Australia

The impact of deferred grazing (no defoliation of pastures for a period generally from spring to autumn) and fertilizer application on plant population density, ground cover and soil moisture in a hill pasture (annual grass dominated, with Australian native grasses being the major perennial species) were studied in a large‐scale field experiment from 2002 to 2006 in southern Australia. Three deferred grazing strategies were used: short‐term deferred grazing (no defoliation between October and January each year), long‐term deferred grazing (no defoliation from October to the autumn break, that is the first significant rainfall event of the winter growing season) and optimized deferred grazing (withholding time from grazing depends on morphological development of the plants). These treatments were applied with two fertilizer levels (nil fertilizer and 50 kg P ha^?1 plus lime) and two additional treatments [continuous grazing (control) and no grazing for year 1]. Deferred grazing increased (P < 0·05) perennial grass tiller density compared with the control. On average, the tiller density of the three deferred grazing treatments was 27–88% higher than the control. There was a negative (P < 0·01) relationship between perennial and annual grass tiller density. Fertilizer application increased (P < 0·05) legume plant density. The densities of annual grasses, legumes, onion grass (Romulea rosea) and broadleaf weeds varied between years, but perennial grass density and moss cover did not. The ground cover of the deferred grazing treatments in autumn was on average 27% higher than the control. Soil moisture differed between treatments at 15–30 cm depth, but not at 0–15 depth over autumn and winter. The results imply that deferred grazing can be an effective tool for rejuvenating degraded native pastures through increases in native grass tiller density and population and through improving farm productivity and sustainability.     

Effect of six-weekly harvests on the yield, chemical composition and dry matter degradability of Panicum maximum and Stylosanthes hamata in Nigeria

The dry matter (DM) yield and degradability of 6‐week‐old harvests of tropical forages were measured over a season. The forages were nitrogen‐fertilized Guinea grass (Panicum maximum, NFG), unfertilized Guinea grass (UFG), Verano stylo (Stylosanthes hamata,VS), a Guinea grass–Verano stylo mixture (GSM) and Guinea grass in the grass–Verano stylo mixture (GGSM). Six‐week‐old forages were made possible through a cutting regime, which produced four harvests in the growing season. The DM yields of the forages differed significantly (P < 0·001) and showed a significant reduction (P < 0·01) across the season. Crude protein and neutral‐detergent fibre concentrations were significantly (P < 0·01) different between the forages but there was no difference between harvests. The DM degradability of the forages at all harvests were significantly (P < 0·001) different with differences in the soluble fraction (a), degradable fraction (b), potential degradability (PD) and effective degradability (ED), but rate of degradability (c) did not show any significant difference between the forages. Significant (P < 0·01) differences were found between harvests for b and PD, and for the interaction between forage and harvest for b, PD and ED but were not found for the a and c fractions. Both the PD and ED values of all the forages fell with advancing harvests. Although the 6‐week‐old harvests of forage were found not to influence the characteristic reduction in yield of tropical grasses over time, it is concluded that such a management system could be used to obtain forage of relatively high nutritive value during the growing season.     

Effect of defoliation management, based on leaf stage, on perennial ryegrass (Lolium perenne L.), prairie grass (Bromus willdenowii Kunth.) and cocksfoot (Dactylis glomerata L.) under dryland conditions. 2. Nutritive value

A field experiment was undertaken between April 2003 and May 2004 in southern Tasmania, Australia, to quantify and compare changes in the nutritive value of perennial ryegrass (Lolium perenne L.), prairie grass (Bromus willdenowii Kunth.) and cocksfoot (Dactylis glomerata L.) under a defoliation regime based on stage of leaf regrowth. Defoliation interval was based on the time taken for two, three or four leaves per tiller to fully expand. At every defoliation event, samples were collected and analysed for acid‐detergent fibre (ADF), neutral‐detergent fibre (NDF) and total nitrogen (N) concentrations and to estimate metabolizable energy (ME) and digestible dry matter (DDM) concentrations. Amounts of crude protein (CP) and metabolizable energy (MJ) per hectare values were subsequently calculated. There was a significantly lower (P < 0·001) NDF concentration for perennial ryegrass compared with prairie grass and cocksfoot, and a significantly lower (P < 0·001) ADF concentration for cocksfoot compared with prairie grass and perennial ryegrass, regardless of defoliation interval. The CP concentration of cocksfoot was significantly greater (P < 0·001) compared with the CP concentrations of prairie grass and perennial ryegrass. The estimated ME concentrations in cocksfoot were high enough to satisfy the requirements of a lactating dairy cow, with defoliation at or before the four‐leaf stage maintaining ME concentrations between 10·7 and 10·9 MJ kg^?1 DM, and minimizing reproductive plant development. The ME concentrations of prairie grass (10·2–10·4 MJ kg^?1 DM) were significantly lower (P < 0·001) than for cocksfoot (as above) and perennial ryegrass (11·4–11·6 MJ kg^?1 DM) but a higher DM production per hectare resulted in prairie grass providing the greatest amounts of ME ha^?1.     

Effects of nitrogen fertilization and cutting intensity on the agronomic performance of warm‐season grasses

Responses of grasses to N fertilization are affected by cutting intensity although little is known regarding the interactions of these factors in warm‐season grasses. Pre‐cutting canopy height, herbage accumulation and changes in the nutritive value of warm‐season grasses in response to four different management strategies were assessed from October 2011 to September 2014. Treatments included two cutting intensities (70 vs. 50% depletion of canopy height set by 95% light interception), two N fertilization levels (zero vs. 300 kg N ha^?1 year^?1) and six perennial C₄ grass species (Axonopus catharinensis; Cynodon spp. hybrid Tifton 85; Hemarthria altissima cv. Flórida; Megathyrsus maximus cv. Aruana; Paspalum notatum cv. Pensacola; and Urochloa brizantha cv. Marandu) grown in monoculture in a factorial experimental design. Canopy height varied among grass species, cutting intensity and N treatments, mainly among seasons, indicating that more than one management target (i.e. canopy height) existed throughout the plant growth cycle for each species. The largest herbage accumulation occurred in the N fertilization treatments for most species, regardless of cutting intensity. Nitrogen fertilization and 50% depletion of canopy height increased the leaf proportion and decreased the neutral detergent fibre content. Overall, N fertilization had a stronger positive impact than cutting intensity on the acid detergent fibre content, dry‐matter digestibility and crude protein content, but the magnitudes of the responses were species‐specific.     

Competition in perennial ryegrass–white clover mixtures under cutting. 2. Leaf characteristics, light interception and dry-matter production during regrowth

The effect of defoliation interval on growth patterns of contrasting perennial ryegrass (Lolium perenne)–white clover (Trifolium repens) mixtures was studied. The dynamics of increase in leaf area, light interception and dry-matter (DM) production were measured within successive regrowth periods. No N fertilizer was applied. During 1995 six mixtures were cut eight (F1) or six times (F2) at a stubble height of 5 cm. The stubble composition was stable throughout the growing season: after harvest about 50 g DM m^?2 (with a white clover proportion of 0·52) was present with a leaf area index (LAI) of 0·5 (0·38 white clover). The percentage of intercepted radiation after cutting was 20–30% and increased during 3 weeks to about 95%. The relative growth rate of leaf area and DM was higher for white clover than for perennial ryegrass, with the proportion of clover in the LAI and DM increasing during each regrowth period. Mixtures with large-leaved white clover cv. Alice had a lower initial clover content after harvest, but a more rapid increase in clover LAI and DM than mixtures with the smaller leaved cvs Gwenda or Retor. Alice had the highest total and clover LAI and DM at harvest. Cutting frequency affected the change in white clover–perennial ryegrass ratio during regrowth. This was significantly higher in mixtures with Alice than in mixtures with Gwenda, but only under less frequent cutting (F2). In spring there was a mean white clover proportion of about 0·55 in the LAI and 0·45 in the total harvested DM. In summer the white clover proportion in the LAI and DM increased to 0·70–0·75. There was a decline during autumn, especially in F2 and in the mixtures with the small-leaved white clover cv. Gwenda and the medium-leaved cv. Retor. In contrast, grass DM and LAI declined from spring to summer. The decline in clover LAI in autumn was similar in Alice and Gwenda at frequent cutting (F1), but stronger in Gwenda in F2. Retor had the lowest clover specific leaf area (SLA). The SLA values of Alice and Gwenda were similar, SLA being similar between cutting treatments. No differences were found for leaf weight ratio (LWR) among the three white clover cultivars or between the grass cultivars, and LWR was not affected by cutting treatment. Defoliation interval had limited effects on the growth pattern and leaf characteristics of perennial ryegrass–white clover mixtures.     

Biomass production and nutrient removal by tropical grasses subsurface drip‐irrigated with dairy effluent

Effluent lagoons on dairy farms can overflow and potentially pollute adjacent land and associated water bodies. An alternative solution to effluent disposal is needed by dairy operators in island environments. An attractive win‐win alternative is to recycle nutrients from this resource through effluent irrigation for forage grass production that minimizes environmental pollution. This study assessed biomass production and nutrient removal by, and high application rates to, tropical grasses that were subsurface drip‐irrigated with dairy effluent. Four grass species – Banagrass (Pennisetum purpureum K. Schumach.), California grass (Brachiaria mutica (Forssk.) Stapf.), Stargrass (Cynodon nlemfuensis Vanderyst) and Suerte grass (Paspalum atratum Swallen) – were subsurface (20–25 cm) drip‐irrigated with effluent at two rates based on potential evapotranspiration (ET_p) at the site (Waianae, Hawaii) ?2·0 ET_p (16 mm d^?1 in winter; 23 mm d^?1 in summer) and 0·5 ET_p (5 mm d^?1 in winter; 6 mm d^?1 in summer). Treatments were arranged in an augmented completely randomized design. Brachiaria mutica and P. purpureum had the highest dry‐matter yield (43–57 t ha^?1 year^?1) and nutrient uptake especially with the 2·0 ET_p irrigation rate (1083–1405 kg ha^?1 year^?1 N, 154–164 kg ha^?1 year^?1 P, 1992–2141 kg ha^?1 year^?1 K). Average removal of nutrients by the grasses was 25–94% of the applied nitrogen, 11–82% of phosphorus and 2–13% of the potassium. Average values of crude protein (90–160 g kg^?1), neutral detergent fibre (570–620 g kg^?1) and acid detergent fibre (320–360 g kg^?1) were at levels acceptable for feeding to lactating cattle. Results suggest that P. purpureum and B. mutica irrigated with effluent effectively recycled nutrients in the milk production system.     

Forage quality of white clover (Trifolium repens L.) × Caucasian clover (T. ambiguum M. Bieb.) hybrids and their grass companion when grown over three harvest years

Interspecific hybrids between white clover (Trifolium repens L.) and Caucasian clover (Trifolium ambiguum M. Bieb.) have been developed to introgress the rhizomatous growth habit into white clover, to increase persistence and drought tolerance. The forage quality of T. repens, T. ambiguum and the backcross 1 (BC1) and backcross 2 (BC2) hybrids and companion grass, when grown in mixtures with an intermediate perennial ryegrass (Lolium perenne L.) under a cutting‐only management, was measured. In vitro dry‐matter digestibility (DMD), water‐soluble carbohydrate (WSC) and crude protein (CP) concentrations of the legume and grass fractions were measured throughout the growing season over three harvest years. Trifolium repens had a lower WSC but a higher CP concentration than the perennial ryegrass companion in all harvest years and at all cuts. The legume fractions from the BC1 and BC2 hybrid plots had a higher WSC and a lower CP concentration but an in vitro DMD value comparable with white clover throughout the growing season and in each harvest year. The grass fractions from the mixtures with the backcross hybrids had a higher WSC and a lower CP concentration than the grass fraction from the T. repens plots, in all harvest years and throughout the growing season. No difference in in vitro DMD between parental species and backcross hybrids was observed. The implications of these results for the development of these hybrids and animal performance are discussed.     

Seeding cool-season grasses into unimproved warm-season pasture in the southern Great Plains of the United States

Limited availability of herbage during the cool season creates a problem of a supply of nutrients for livestock producers throughout the southern Great Plains of the USA and, particularly, on small farms where resource constraints limit possible mitigating strategies. Six cool‐season grasses were individually sown into clean‐tilled ground, no‐till drilled into stubble of Korean lespedeza [Kummerowia stipulacea (Maxim) Makino] or no‐till over‐sown into dormant unimproved warm‐season pastures. The dry matter (DM) yields of mixtures of cool and warm‐season herbage species were measured to test their potential for increasing cool‐season herbage production in a low‐input pasture environment. Only mixtures containing Italian ryegrass (Lolium multiflorum Lam) produced greater year‐round DM yields than undisturbed warm‐season pasture with all establishment methods. When cool‐season grass was no‐till seeded into existing warm‐season pasture, there was on average a 0·61 kg DM increase in year‐round herbage production for each 1·0 kg DM of cool‐season grass herbage produced. Sowing into stubble of Korean lespedeza, or into clean‐tilled ground, required 700 or 1400 kg DM ha^?1, respectively, of cool‐season production before the year‐round DM yield of each species equalled that of undisturbed warm‐season pasture. Productive pastures of perennial cool‐season grasses were not sustained beyond two growing seasons with tall wheatgrass [Elytrigia elongata (Host) Nevski], intermediate wheatgrass [Elytrigia intermedia (Host) Nevski] and a creeping wheatgrass (Elytrigia repens L.) × bluebunch wheatgrass [Pseudoroegneria spicata (Pursh)] hybrid. Lack of persistence and low productivity limit the usefulness of cool‐season perennial grasses for over‐seeding unimproved warm‐season pasture in the southern Great Plains.     

Field indicators of leaf nutritive value for perennial ryegrass and tall fescue pastures under different growing and management conditions

Field indicators of forage nutritive value could help farmers with rapid management decisions to optimize timing and intensity of grazing and meet objectives regarding animal nutrition. The objective of this research was to evaluate the likely relationships among leaf blade nutritive value, herbage mass and leaf stage of pasture regrowth under different growing seasons and residual sward heights. Experiments were performed on perennial ryegrass (Lolium perenne L.) and tall fescue (Festuca arundinacea Schreb.) pastures during spring and summer of 2016. In both pastures, three residual sward height treatments (3, 6 and 12 cm) were imposed on plots arranged in a split plot design, replicated in three blocks. Sward plots were harvested 5–6 times at intervals spaced 7–10 days apart to measure herbage mass, plant morphology, neutral detergent fibre (NDF), and the 24-hr in vitro digestibility of NDF (NDFD) and dry matter (DMD) of leaf blades. Pastures showed strong (R²: .62 to .70), but variable, negative relationships between NDFD and herbage mass that varied with the rate at which pasture grew in each season of experimentation. Although there was a consistent NDFD decline as leaf stage of regrowth progressed (R²: .75 to .97), the NDFD also decreased as residual sward height increased, most notably in tall fescue. Additionally, findings indicate that the greater leaf length plasticity of tall fescue compared to residual sward heights may offer opportunities to manage both post- and pre-grazing targets to achieve tall fescue forages with a similar high nutritive value as perennial ryegrass. However, the evaluation of this hypothesis at the farm level and its impacts on animal intake and performance warrants further careful investigations.     

Grass weed control in sunflower in the spring and kharif (summer) seasons under barani (rainfed) conditions in Pakistan

In field trials conducted at the National Agricultural Research Centre (NARC) near Islamabad and in farm fields, control of grass weeds including Cynodon dactylon (bermudagrass), Sorghum halepense (johnsongrass), Echinochloa colonum (junglerice) and Dactyloctenium aegyptium (crowfootgrass) increased yields of sunflower by 25–100%. The trials were conducted in the spring (February–May) and kharif (July–October) seasons in 1985 and 1986. Hand weeding generally resulted in the greatest yield response but this method was highly labour intensive and considered to be impractical by local farmers. The average time required to maintain 1 ha weed free in the spring and kharif seasons was 41 and 90 eight-hour man-days, respectively. In three of four trials conducted in the spring season, fluazifop-butyl at 0·25 and 0·5 kg/ha did not provide satisfactory control of grass weeds and did not result in significant increases in sunflower seed yields. The performance of fluazifop-butyl in these trials was adversely affected by hot dry conditions causing severe moisture stress after treatment. In contrast, in the fourth spring trial at NARC in 1986 and in all kharif season trials, fluazifop-butyl at 0·25 kg/ha effectively controlled both annual and perennial grasses and resulted in seed yields comparable to those obtained by hand weeding. Value/cost ratios indicate that, in the spring season under drought stress conditions, application of the herbicide would not be profitable; however, in the kharif season, herbicide treatment to control actively growing grass weeds would provide a cost-effective alternative to hand weeding.     

Estimation of extractable protein in botanical fractions of legume and grass species

With a globally strong interest in bio‐based products such as fuels and chemicals, a feasible source of protein for the industry with positive economic impacts could be from leaves. However, more knowledge is needed on how to improve the content of extractable protein. Grasses and legumes have a high content of protein with a favourable amino acid composition. The extractable true protein was estimated at two harvest dates in leaf and stem of the legume species white clover (Trifolium repens L.), red clover (Trifolium pratense L.) and lucerne (Medicago sativa L.) and the grass species perennial ryegrass (Lolium perenne L.) and tall fescue (Festuca arundinacea L.) using the Cornell Net Carbohydrate and Protein System. Extractable true protein was more concentrated in the leaf than in the stem of all the species. Easily extractable true protein in the leaf constituted 63%–68% and 54% of crude protein in legumes and grasses respectively. If the cell wall‐bound true protein in the leaf can be extracted, concentration of extractable true protein may increase by 7%–14% and 21%–26% of crude protein in legume and grass respectively. Legume leaf could be superior to grass leaf for protein production in a biorefinery due to higher extractable true protein both on a mass basis and per hectare. In white clover leaf, a significant decline in concentration of extractable true protein with maturity was simultaneous with a substantial increase in extractable true protein per hectare.     

Soil water dynamics and dry‐matter production of old man saltbush‐, native grass‐ and lucerne‐based pastures in a variable summer‐dominant rainfall environment,Australia

In a summer‐dominant high‐rainfall, yet seasonally dry environment, soil water dynamics and dry‐matter (DM) production were monitored during 2006–12, for three perennial pasture types: old man saltbush (Atriplex nummularia ssp. nummularia with native grass), native grass (Bothriochloa macra and Rytidosperma bipartita dominant) and lucerne (Medicago sativa cv. Venus). Plant root depth of the old man saltbush pasture (1·5 m) was greater than that of native grass (1·2 m), but equal to that of lucerne (1·5 m), resulting in equivalent levels of maximum extractable water (MEW; mm, 0–1·7 m) for saltbush and lucerne in five of the six seasons. Lucerne (MEW 242 mm) extracted more soil water than native grass (144 mm), but was similar to old man saltbush (205 mm). In the second year of growth, both the lucerne and old man saltbush pastures achieved their maximum yields of 16·8 and 7·9 t DM ha^?1 respectively, but thereafter declined. The decline in yield of lucerne in later years was associated with a significantly lower plant frequency and increase in proportion of weeds. The decline in yield of old man saltbush appeared to be associated with an increasingly dry soil profile, despite receiving rainfall that was above average. The yield of the native grass pasture increased during the study as the proportion of weeds declined, and the presence of saltbush plants did not compromise the yield of perennial grasses in the inter‐row spaces. The implications of these findings for livestock production systems in this environment are discussed.     

TILLERING IN GRASSES—ITS SIGNIFICANCE AND CONTROL*

Tillering is examined in relation to the morphology and habit of growth of the perennial herbage grasses; particular reference is made to the effects of cutting and grazing. The importance of tillering in establishment and regeneration or perennation of a grass sward is considered; greater importance is attached to the role of tillers in the regrowth of swards cut for conservation at the reproductive stage of growth. Amounts of regrowth are related to both the number and size of vegetative tillers present at the base of reproductive tillers at the time of cutting. The probable inhibition of the replacement tiller buds by the developing inflorescence is suggested as a reason for the poor growth of grass swards in the favourable environment of midsummer. The physiological mechanisms which control tillering during reproductive development are examined. Spring and winter wheat (Triticum aestivum), Lolium temulentum and Phalaris tuberosa are used as physiological tools to demonstrate that tillering is restricted during reproductive development, and that stem extension may be more important than changes at the stem apex in controlling this restriction of tillering at the base of the inflorescence-bearing stem. It appears from results of the application of a range of growth regulators that substances derived from the meri-stematic centres, in either the elongating stem or the terminal meristem, indirectly control the metabolic activity of the lateral buds from which new tillers are derived. The degree of apical dominance is shown to depend on the light intensity in which the plants are grown. Finally, the physiological results are used to suggest reasons for the commonly found apparent inability of heavily fertilized perennial ryegrass (Lolium perenne) swards to regrow after cutting at the inflorescence-emergence stage of growth.     

Comparative defoliation tolerance of temperate perennial grasses

The defoliation tolerance of cultivars of four temperate perennial pasture grasses, perennial ryegrass (Lolium perenne, cv. Yatsyn1), phalaris (Phalaris aquatica cv. Australian), tall fescue (Festuca arundinaceae cv. Demeter) and cocksfoot (Dactylis glomerata cv. Porto), was determined under controlled conditions over a period of 12 weeks. Undefoliated plants were compared with defoliated plants, where only half of one leaf was left intact at the initial defoliation, and leaf regrowth was harvested every 3–4 d. The growth responses measured were plant tiller number, dry weight, relative leaf regrowth rate, root:shoot ratio, sheath:stem ratio and specific leaf weight. All species showed morphological adaptations that potentially increased their ability to tolerate defoliation (e.g. increased allocation to shoot at the expense of roots and lower specific leaf weights) but cocksfoot was found to be the most defoliation‐tolerant and perennial ryegrass the least. The adaptation that favoured cocksfoot most strongly was high sheath:stem ratio, which, it is proposed, allowed it to maintain photosynthesis and a level of carbon supply sufficient to support regrowth throughout the experiment. The strategy of perennial ryegrass which favours leaf growth and leads to rapid leaf turnover rates made it particularly susceptible to defoliation under the conditions of this experiment. This highlights the likely importance of defoliation‐avoidance responses in explaining the well‐known grazing resistance of this species. Phalaris and tall fescue showed responses that were intermediate between the other two species. The importance of defoliation‐avoidance mechanisms and implications for grazing management are discussed.