Perennial Swards Research Articles

Halo‐hydromorphism alters nitrogen fertilization responses of tall wheatgrass pastures: Capture and use of resources, tiller dynamics and forage production

AbstractHalo‐hydromorphism limits productivity in approximately 100 million hectares worldwide. Tall wheatgrass (Thinopyrum ponticum) is a species widely used in these environments for its seeding potential, being the addition of nitrogen a considered technological tool to increase forage quality and production. The objective of the study was to determine the impact of nitrogen fertilization on the capture and use of resources (radiation, water and nitrogen) in a cool season perennial sward growing in contrasting halo‐hydromorphic conditions. Cultivated pastures from three independent sites were used. Sites were described according to the degree of halo‐hydromorphism using soil salinity and water table attributes (salinity and depth) as environmental indicators: low HHM site [electrical conductivity (EC1:2.5) 0.97 dS/m; water table salinity 2.03 dS/m; depth 85 cm], intermediate HHM site (EC1:2.5 3.86 dS/m; water table salinity 7.40 dS/m; depth 134 cm) and high HHM site (EC1:2.5 4.49 dS/m; water table salinity 7.85 dS/m; depth 31 cm). At each site, a late spring regrowth (~750°Cd) was studied by applying two treatments (n = 5): without (N0) and nitrogen fertilization (N150; 150 kg/ha of nitrogen in the form of urea). The response of tall wheatgrass to nitrogen fertilization in halo‐hydromorphic conditions depends on soil salinity and water table attributes. N150 treatments production was twice as high as in N0 in low HHM and intermediate HHM environments (from 1750 to 3500 kgDM/ha and from 1080 to 1985 kgDM/ha, respectively). Meanwhile, in high HHM conditions, forage production was only 40% higher when nitrogen was added (from 625 to 870 kgDM/ha). In low HHM the higher N150 production was related to tiller density and size, whereas in intermediate HHM and high HHM was linked only to tiller size. In N150 treatments, the nitrogen nutrition index was negatively affected with the increase in HHM conditions (0.77, 0.62 and 0.55 for low HHM, intermediate HHM and high HHM, respectively). Instead, nitrogen nutrition index of N0 was similar in all the environments (~0.42). In N150, forage production capacity analysed in terms of radiation and water use efficiency (RUE and WUE, respectively) was similar in low HHM and intermediate HHM environments (RUE ~0.81 gDM/Mj and WUE ~13 kgDM/mm). These findings emphasize the importance of conducting analyses based on resource use and capture to understand productive responses to the increase in growth‐limiting factors. Furthermore, they contribute to the identification of environments suitable for nitrogen fertilization.

Making the Wakehurst prairie

SummaryThe creation of the North American prairie gardens at Wakehurst Place is described, with details of different stages in the planting, designed to form a species‐rich perennial sward which will be self‐sustaining.

N2 Use in Perennial Swards Intercropped with Young Poplars, Clone I-214 (Populus × euramericana (Dode) Guinier), in the Mediterranean Area under Rainfed Conditions

Intercropping perennial legumes with trees can reduce Nitrogen (N) losses, due to the high amount of N accumulated in stable forms in the soil and permanent soil cover during the whole year. Although N cycling improvement in mature agroforestry systems (AFS) was well documented, there is a lack of knowledge regarding systems in transition to AF. In this work, we studied the association of two perennial forage crops, namely ryegrass (Lolium multiflorum Lam.) and sulla (Hedysarum coronarium L.), with 1-year old poplars, to evaluate: (i) the agronomic performance of sulla and ryegrass with vs. without intercropped poplar trees; (ii) the N-fixing ability of sulla in association with trees; (iii) the N transfer effect from sulla and growth promoting effect on poplar; and finally (iv) the nitrate leaching reduction due to the presence of poplar trees associated to forage crops. The layout was arranged in a two-factor randomized complete blocks design (RCB) with three replicates. The first factor tested (crop species) implied two different swards, namely sulla and ryegrass. The second factor (cropping system) included two different systems: PAST i.e., a pastoral system without trees, and SIPAST, i.e., a silvo-pastoral system with one poplar tree row beside the sward. Sulla resulted more productive than ryegrass when associated with trees (+35%). No clear trend was observed about the tree influence on N-fixation in sulla, but the amount of N fixed resulted higher in in sulla grown in the SIPAST near the trees (+35%). Poplar plants, even in the first year after planting, resulted effective yet in reducing the nitrate flux from the crops towards ditches. Further investigations are needed to study other swards in young AF and better understand the N dynamics; in particular, it could be worth to assess the nutrient flux in the soil solution.

Dry‐matter production and botanical composition of multispecies and perennial ryegrass swards under varying defoliation management

AbstractMultispecies swards, comprised of different plant functional groups have comparable production potential to high N input L. perenne swards at reduced N when legumes are included. However, information on the appropriate management of multispecies swards is limited. The effect of differing management practices on the herbage dry‐matter (DM) production and botanical composition of different sward types was investigated using a 3 × 2 × 2 factorial design plot experiment. The experiment consisted of three sward types: L. perenne‐only receiving (LP; 250 kg N ha−1 a−1); L. perenne‐Trifolium repens (LP‐TR); multispecies sward containing L. perenne, Phleum pratense, Trifolium repens, Trifolium pratense, Plantago lanceolata and Cichorium intybus (MSS). LP‐TR and MSS received 90 kg N ha−1 a−1. Harvesting of plot herbage took place every 21 or 28 days to a defoliation height of 4 or 6 cm, over two growing seasons (March to November 2020 and 2021 inclusive). Annual herbage produced by both LP and LP‐TR was not significantly affected by defoliation frequency. However, MSS produced 1923 kg DM ha−1 a−1 more herbage when harvested less frequently. Unsown species contributed significantly less to the herbage DM of MSS compared to LP and LP‐TR and remained similar in 2020 and 2021, whereas the contribution of unsown species to herbage DM increased in LP and LP‐TR from 2020 to 2021, with noxious species more associated with LP and LP‐TR than MSS. Results demonstrate the role of multispecies swards in improving the sustainability of grass‐based agricultural systems in an environment of reduced fertilizer inputs.

Emergency seeding of cool‐season annuals into perennial grass after fall drought

AbstractSpring establishment of cool‐season annual grasses into poorly producing orchardgrass (Dactylis glomerata L) (OG) swards may improve forage production and nutritive value in the southeastern United States following a fall drought. A randomized complete block experiment was conducted where annual ryegrass (Lolium multiflorum Lam.) (AR) or forage oat (Avena sativa L.) (FO) was interseeded into an existing OG stand over three seeding dates with (+) or without (–) a burndown herbicide (BD) treatment and compared with an OG monoculture (control). In 2017, after a warm and wet winter, the OG monoculture (control) was able to produce sufficient forage mass (FM) without significant reduction in nutritive value as compared with OG interseeded with AR or FO. In 2018, OG had approximately 2,600 lb acre–1 less FM than in 2017, suggesting that recurrent fall drought with unfavorable winter conditions resulted in long‐term damage to the perennial sward. Meanwhile, treatments without BD did not show higher FM in the beginning of the season. Burndown treatment in general increased FM and nutritive value. An economic analysis of the study also revealed results suggesting that interseeding AR and FO in the spring is not economically viable, as it may cost up to 10 times as much as the control.

Last tesserae of a fading mosaic: floristic census and forest vegetation survey at Parche di Bilello (south-western Sicily, Italy), a site needing urgent protection measures

This paper illustrates the botanic heritage of Parche di Bilello, a site located in the municipality of Castelvetrano. The study area hosts several woodland fragments dominated by Olea europaea var. sylvestris, Quercus suber and Quercus ilex, respectively. According to historical data, these nuclei represent the last remnants of an open forestland which covered a much wider coastal area between Mazara del Vallo and Sciacca until the end of Middle Age. Phytosociological relevés were focused on these forest nuclei, probably the most representative of south-western Sicily, which correspond to three habitats included in the 92/43 EEC Directive (9320, 9330 and 9340, respectively) and represent the final stage of three different edaphic series. Wild olive forests probably dominated on sandy calcareous soils, holm oaks prevailed on steep calcareous and N-exposed slopes. In contrast, cork oaks mostly occurred on sandy subacid soils issuing from pedogenetic processes on palaeodunes. Moreover, field surveys allowed to list 331 vascular plant taxa. Among them, Linaria multicaulis subsp. humilis, Orobanche balsensis and Serapias orientalis subsp. siciliensis are new to Trapani Province. Detailed information on the current distribution and the synecology of several plant taxa of high biogeographic and conservation interest is also provided. The study site also hosts one habitat of priority interest (6220, i.e. xerophilous Mediterranean perennial grasslands and annual swards) and two species protected by international laws, i.e. the orchid Ophrys lunulata and the lichen Teloschistes chrysophthalmus. Considering the high value of its natural heritage, this territory deserves the adoption of more effective protection measures. For this reason the authors recommend its inclusion as a new Site of Community Interest within the Sicilian Natura 2000 network.

The intensity of water stress dictates whether the N status of temperate-type perennial grass swards is affected by drought

Abstract Temperate-type, summer-active cool-season perennial grasses are frequently exposed to dry spells during the warm season due to the high atmospheric demand and fast soil desiccation. Since water availability is essential for sward nitrogen (N) uptake and most mineral N is located in the topsoil, water stress may hinder sward N nutrition if it reduces N supply. In hydro-halomorphic soils, imbalances between soil N supply and sward N demand during summer could be further aggravated by, first, the limited water holding capacity of the topsoil, and second, potential availability of water from deep, N-poor soil horizons that are kept moist by a shallow water table. The aim of this work was to quantify the effect of N and water availability on N status and productivity of temperate-type perennial swards growing in a hydro-halomorphic soil of the Flooding Pampa. During two consecutive years, shoot and root dynamics, as well as radiation capture, N nutrition index (NNI), soil water availability and leaf water potential were followed over six weeks long mid-summer regrowths of old stands (>9 years) of temperate-type tall fescue [Lolium arundinaceum (Schreb.) Darbysh.] sown on a typical Natraqualf soil in Balcarce, Argentina. Swards were either rainfed or irrigated and fertilized with either 40 or 200 kg de N ha−1. Root systems were large (5.8–9.3 Mg DM roots ha−1), but concentrated mostly in the 0.2 m topsoil (66%–75% of root biomass or length). Despite invariably high available water below 0.4 m throughout both experimental periods, rainfed swards faced transient episodes of water stress whenever the upper soil layer dried out. Tall fescue swards were strongly co-limited by water and N during summer, showing comparable, very high responses to both N addition and irrigation. Further, forage yield showed synergistic increases when swards received both supplemental water and N simultaneously. This was mainly due to consistent synergistic responses in radiation use efficiency and leaf lifespan. Sward NNI was depressed only by an historically severe drought but was not altered when water stress intensity was lower, close to average for the season in the area. Therefore, the major causes of typically low summer productivity of temperate-type tall fescue growing in hydro-halomorphic soils of the Flooding Pampa are the intrinsic effects of low N and low water availability, with only uncommonly extreme water stress episodes reducing yield indirectly through an aggravation of crop N status.

Towards an objective evaluation of persistency of Lolium perenne swards using UAV imagery

Perennial ryegrass (Lolium perenne) is a perennial crop used in temperate regions as forage. In L. perenne breeding programs, persistency is an important trait. Poor persistency results in sward degradation and associated yield and nutritive value losses. Breeders assess persistency of accessions using visual scoring in field plots during the 2nd or 3rd growing season. This evaluation system is easy and cheap but is not free from human bias. In this study, the correlation between the scoring done by different breeders was only 0.243. As an alternative we have developed a methodology to assess persistency of L. perenne breeding materials based on vegetation indices (VIs) derived from Unmanned Aerial Vehicle (UAV) imagery. The VIs Excess green (ExG2), Green Leaf Index and Normalized green intensity (GCC) were found to provide consistent results for flights carried out under different light conditions and were validated by ground reference information. The correlation between the VIs and the percentage of ground cover extracted from on-ground imagery was 0.885. To test the implementation of the method we compared the ExG2 value based approach to selection with a visual score based selection methodology as applied by two breeders. The breeding decisions of Breeder A agreed well with decisions based on ExG2 values (74.6%), but those of Breeder B displayed a lower agreement (54.0%). In contrast, agreement between decisions based on different flights was very high (91.6%). The methodology was validated for general applicability. In summary, the results demonstrate that basing persistency selection in L. perenne breeding programs on ExG2 values from UAV imagery is likely to be more objective in comparison to the currently-used visual scoring method.

Performance of Heifers Grazing Bermudagrass Pastures Strip or Solid Seeded with Clovers

Core Ideas Strip‐seeding of clovers into bermudagrass swards resulted in similar clover stand percentage compared with solid planting of clovers. Heifers grazing pastures that were strip seeded performed similarly to heifers grazing clovers that were seeded in solid stands. Red clovers persisted longer into the summer than either white or subterranean clovers. Red clover provided greater animal performance than white and subterranean clovers. Even though clovers can provide improved forage quality and reduced N fertilization when grazing stocker calves on warm‐season grass pastures, stand establishment remains a concern. The objective of this research was to determine if alternative methods of seeding legumes into warm‐season perennial swards could improve legume establishment. This research took place on 18, four‐acre mixed bermudagrass [Cynodon dactylon (L.) Pers.], crabgrass [Digitaria ciliaris (Retz.) Koeler], and dallisgrass (Paspalum dilatatum Poir.) pastures at the University of Arkansas Southwest Research and Extension Center Stocker Unit. Pastures were seeded in October of 2013 to white (Trifolium repens L.), red (Trifolium pratense L.), or subterranean (Trifolium subterraneum L.) clovers either in solid stands at the recommended rate (2.0, 8.0, and 11 lb/acre, respectively) or in four 0.25‐acre strips at twice the recommended seeding rate in a 3 × 2 factorial arrangement of treatments with three pasture replications per treatment combination. Growing heifers (n = 216; 614 ± 44.4 lb) grazed pastures from May to September 2014 and April to September 2015. Red clover was present later into the summer than white or subterranean clovers, but there were no differences due to seeding method. At the end of the grazing season, heifer bodyweight and gain was greater when grazing red clover than when grazing subterranean clover. Strip‐seeded clovers in only 50% of the pasture area provided similar stands to conventional solid seeding and equivalent animal performance. Red clover grew later into the summer grazing season and provided greater animal performance than white and subterranean clovers.

Effects of pasture base and species mix complexity on persistence and weed ingress in summer-dry dairy pastures

Basal and canopy cover of sown and unsown species in swards sown with six species mixtures were assessed monthly from autumn 2010 to spring 2014, to test the hypotheses that (a) sowing an alternative pasture base, or (b) increasing the complexity of the sown mix, improves persistence and reduces weed ingress in temperate summer-dry dairy pastures. Treatments comprised either perennial ryegrass (Lolium perenne L.) infected with AR1 endophyte or tall fescue (Schedonorus arundinaceus (Schreb.) Dumort.) infected with Max P endophyte to which were added either a legume (‘standard’, 2-species mix), a legume and two forage herbs (‘herbs’, 4-species), or three legumes, two forage herbs and two grasses (‘complex’, 8-species). In the first year, basal and canopy cover of sown species were higher in perennial ryegrass- than tall fescue-based swards, and basal cover of sown species was higher and the percentage bare ground lower in the ‘standard’ (50%) than ‘herbs’ and ‘complex’ swards (42%). By the final year, basal cover of sown species (25%), unsown species (28%), and percentage bare ground (47%) were similar in all six treatments. Although establishment was greater in perennial ryegrass than tall fescue-based swards and in the ‘standard’ than in the ‘herbs’ and ‘complex’ mixtures, the loss of sown species in these treatments was greater. The decline in basal cover of sown species was –27% in the standard treatment, –16% averaged over the ‘complex’ and ‘herbs’ treatment, –24% in perennial ryegrass-based swards and –15% in tall fescue-based swards. The results are contrary to both hypotheses with respect to weed ingress. However, support was provided for the hypotheses in the greater persistence (smaller decline over time in basal cover) in tall fescue than ryegrass-based swards, and ‘herbs’ and ‘complex’ than ‘standard’ mixtures.

Effect of supplementation with fish oil or microalgae on fatty acid composition of milk from cows managed in confinement or pasture systems

The objective of this study was to examine the interaction between lipid supplement (LS) and management system (MS) on fatty acid (FA) composition of milk that could affect its healthfulness as a human food. Forty-eight prepartal Holstein cows were blocked by parity and predicted calving date and deployed across pasture (PAS; n=23) or confinement (CONF; n=25) systems. Cows within each system were assigned randomly to a control (no marine oil supplement) or to 1 of 2 isolipidic (200g/d) marine oil supplements: fish oil (FO) or microalgae (MA) for 125±5d starting 30d precalving. The experiment was conducted as a split-plot design, with MS being the whole-plot treatment and LS as the subplot treatment. Cows were housed in a tie-stall barn from −30 until 28±10d in milk (DIM) and were fed total mixed rations with similar formulations. The PAS group was then adapted to pasture and rotationally grazed on a perennial sward until the end of the experiment (95±5 DIM). Milk samples were collected at 60 and 90 DIM for major components and FA analyses. Milk yield (kg/d) was lower in PAS (34.0) compared with CONF (40.1) cows. Milk fat percentage was reduced with MA compared with FO (3.00 vs. 3.40) and the control (3.56) cows. However, milk fat yield (kg/d) was not affected by lipid supplements. Compared with CONF, PAS cows produced milk fat with a lower content of 12:0 (−38%), 14:0 (−28%), and 16:0 (−17%), and more cis-9 18:1 (+32%), 18:3 n-3 (+30%), conjugated linoleic acid (CLA; +70%) and trans 18:1 (+34%). Both supplements, regardless of MS, reduced similarly the milk fat content of 16:0 (−12%) and increased CLA (+28%) and n-3 long-chain polyunsaturated FA (n-3 LC-PUFA; +150%). Milk fat content of trans 18:1 (trans-6 to trans-16) was increased with FO or MA, although the effect was greater with MA (+81%) than with FO (+42%). The interaction between MS and LS was significant only for trans-11 18:1 (vaccenic acid, VA) and cis-9,trans-11 CLA (rumenic acid). In contrast to CONF, feeding FO or MA to PAS cows did not increase milk fat content of VA and rumenic acid. We concluded that compared with CONF, milk from PAS cows had a more healthful FA composition. Feeding either FO or MA improved n-3 long-chain polyunsaturated FA and reduced levels of 16:0 in milk fat, regardless of MS, but concurrently increased the trans 18:1 isomers other than VA, at the expense of VA, particularly in grazing cows.

Implications of dairy systems on enteric methane and postulated effects on total greenhouse gas emission

The effects of feeding total mixed ration (TMR) or pasture forage from a perennial sward under a management intensive grazing (MIG) regimen on grain intake and enteric methane (EM) emission were measured using chambers. Chamber measurement of EM was compared with that of SF6 employed both within chamber and when cows grazed in the field. The impacts of the diet on farm gate greenhouse gas (GHG) emission were also postulated using the results of existing life cycle assessments. Emission of EM was measured in gas collection chambers in Spring and Fall. In Spring, pasture forage fiber quality was higher than that of the silage used in the TMR (47.5% v. 56.3% NDF; 24.3% v. 37.9% ADF). Higher forage quality from MIG subsequently resulted in 25% less grain use relative to TMR (0.24 v. 0.32 kg dry matter/kg milk) for MIG compared with TMR. The Fall forage fiber quality was still better, but the higher quality of MIG pasture was not as pronounced as that in Spring. Neither yield of fat-corrected milk (FCM) which averaged 28.3 kg/day, nor EM emission which averaged 18.9 g/kg dry matter intake (DMI) were significantly affected by diet in Spring. However, in the Fall, FCM from MIG (21.3 kg/day) was significantly lower than that from TMR (23.4 kg/day). Despite the differences in FCM yield, in terms of EM emission that averaged 21.9 g/kg DMI was not significantly different between the diets. In this study, grain requirement, but not EM, was a distinguishing feature of pasture and confinement systems. Considering the increased predicted GHG emissions arising from the production and use of grain needed to boost milk yield in confinement systems, EM intensity alone is a poor predictor of the potential impact of a dairy system on climate forcing.

Land-use influence on Mediterranean perennial swards of "Poa bulbosa": a case study in the International Tagus Region

Pastureland abandonment or intensification of livestock activity change the floristic patterns of Mediterranean perennial swards which are very important to the conservation of some bird species. The objectives of this study are: 1) to recognise floristic patterns in Mediterranean perennial swards of Poa bulbosa; 2) to identify the communities that configure the European priority habitat 6220* (Pseudo-steppe with grasses and annuals of the Thero-Brachypodietea); 3) to assess the effects of land-use management on the floristic composition of these communities. Field research was conducted in central eastern and south eastern main land Portugal.Vegetation sampling was carried out in 2009-2010 on 9 sward sites, following the phytosociological concepts. Classification and ordination of relevés were obtained by Two Way Indicator Species Analysis (TWINSPAN), Canonical Correspondence Analysis (CCA) and Detrended Canonical Correspondence Analysis (DCCA). Monte Carlo Permutation Tests were performed to analyse differences in floristic patterns. Livestock load, stoniness and land-use history of the last 10 years were selected as the key variables that best explain the ordination model. The absence of extensive livestock grazing results in a reduction of Trifolium subterraneum-dominated areas and in a density/ cover reduction of Poa bulbosa-dominated areas. High livestock loads change the floristic patterns of Mediterranean short swards by favouring species of the Stellarietea mediae class. The control of woody vegetation through grazing or cutting is a key conservation measure.

Does it matter if herbivory is selective? Responses of an endangered herbaceous legume to experimental grazing

Background: Herbivory and inter-specific competition are major determinants of the relative abundance of plant species in grasslands. Herbivores modify competitive hierarchies among plants through selective foraging and as a result of variation in the relative tolerance of plants to herbivory. Aims: We examined the direct effects of herbivory and the role of herbivore preference on the growth, flowering and abundance of an endangered perennial legume, Cullen parvum (F. Muell.) J.W. Grimes, in a temperate Australian grassland grazed by sheep. Methods: Hand clipping was used to simulate herbivory. In each of two populations, three replicates of the factorial combination of C. parvum defoliation (C. parvum grazed or ungrazed), neighbour defoliation (neighbouring vegetation grazed or ungrazed) and three defoliation frequency treatments were randomly applied to 0.25-m2 quadrats containing C. parvum ramets. Results: The abundance, growth and flowering of C. parvum were similarly reduced by both selective and non-selective herbivory. When neighbouring vegetation but not C. parvum was defoliated, growth and abundance were similar and in some cases less than when both neighbours and C. parvum were ungrazed, suggesting little above-ground competitive effect of the grassland sward. Conclusions: The interactions between herbivory and shoot competition by dominant perennial grassy swards had little influence on the growth and abundance of C. parvum. Rather, direct effects of defoliation dominated and we predict that the species persistence in grazed grasslands will be influenced more by poor tolerance of herbivory than by how herbivores modify the competitive effect of neighbouring vegetation.

Influence of photosynthetically active radiation on diurnal N2O emissions under ruminant urine patches

Nitrous oxide (N2O) is a greenhouse gas and is also recognized as the single most important ozone depleting emission. Static chambers are commonly used to measure N2O fluxes from agricultural soils with fluxes measured over approximately 1 hour typically extrapolated to a daily flux, thus assuming a constant flux over 24 h. Diurnal variation in soil N2O fluxes may lead to inaccurate inventory calculations. The aim of this study was to assess the effect of diurnal changes in photosynthetically active radiation (PAR) on N2O emissions from planted and non-planted soil exposed to bovine urine. The effects of varying PAR, over a 16 h day length, on N2O emissions were observed in a split-split plot factorial experiment conducted in the New Zealand Biotron under constant soil and air temperatures. Treatments included absence or presence of both bovine urine and a 1-month-old perennial ryegrass (Lolium perenne) sward. Diurnal N2O fluxes were determined every 1.5 h on days 6 and 19 after urine deposition when ammonium (NH4 +) and nitrate (NO3 −) were expected to dominate the soil inorganic-N pool, respectively. On day 6, NH4 + dominated the soil inorganic-N pool and N2O-N fluxes were relatively low with diurnal amplitudes of 0.5–3.4. By day 19, the soil NO3 − pool had increased as did N2O-N fluxes along with diurnal amplitudes (2.1–41.7). The highest N2O-N fluxes occurred in the soil plus urine treatment as a consequence of PAR altering soil temperature and not as a direct consequence of PAR effects on grass. Diurnal fluxes of N2O-N following ruminant urine deposition to pasture did not occur as a direct result of diurnal PAR cycles potentially affecting root exudation. It is assumed that other sources of C, such as solubilized organic matter, dominated as a microbial C source for denitrifiers.

Sward and tiller growth dynamics of Lolium perenne L. as affected by defoliation frequency during autumn

A mini-sward study was undertaken between January and September 2008 in Valdivia, Chile, to quantify and compare changes in the herbage production, growth dynamics and nutritive quality of a Lolium perenne sward during autumn in response to different nitrogen (N) application regimes and defoliation frequencies. The N levels used in the present study corresponded to the equivalent of an autumnal application of 0, 25 or 75 kg N/ha. The defoliation frequency was based on leaf regrowth stage, and corresponded to the time taken for 1.5, 2.5 or 3.5 leaves per tiller to expand. The growth dynamic measurements were also related to temperature. The results showed that the level of N had no effect on the studied variables. Plants defoliated at the 3.5-leaf stage showed a higher herbage production, higher tillering and a more balanced nutritional profile than plants cut at the 1.5-leaf stage. The defoliation interval had no effect on leaf elongation or leaf appearance. The leaf elongation rate was linearly related to the mean daily temperature (P < 0.01), and the accumulated leaf and tiller number showed a significant linear relationship (P < 0.01) with the thermal time expressed as growing degree days. From the defoliation frequencies tested here, we can conclude that the best time for grazing L. perenne swards during autumn is at the 3.5-leaf stage due to a higher herbage production, higher tillering rate, more balanced nutritive quality and higher reserve levels of the plant, which provide a more favourable background for subsequent growth.

Impact of floor vegetation on the abundance of nematode trophic groups in vineyards

This study examined the effect of two floor vegetation management strategies on the abundance of nematode trophic groups in two Australian vineyards (one cool and one warm climate) for three consecutive years. Throughout the grape growing season floor vegetation was managed either as a perennial sward by regular mowing/snipping (permanent sward) or eliminated by spraying herbicide (spray/bare soil). Soil from both treatments was inhabited by five nematode trophic groups namely bacteria feeders, predators, omnivores, fungal feeders and plant parasites. Of these, bacteria feeder nematodes were predominant, comprising 60–70% of the total population in each site. Predators and plant parasites comprised ca. 3% and 17% of the total population respectively at Wagga Wagga, and ca. 17% and 4% at Tumbarumba. In the sward plots by the end of the experiment, the populations of non-plant parasitic ‘beneficial’ nematodes (bacteria feeders, predators, omnivores and fungal feeders) had generally increased linearly with time whereas plant parasitic nematode populations had decreased. On the last sampling date, the total bacteria feeder nematode populations were ca. 3–4-fold and ca. 2–3-fold greater in the sward than the spray plots at Wagga Wagga and Tumbarumba vineyard respectively. Over three years, the omnivore nematode (primarily Dorylaimidae) populations were also significantly increased by ca. 2–6-fold and 3-fold in the sward plots compared to the spray plots at Wagga Wagga and at Tumbarumba vineyard respectively. Similarly, predatory nematodes in the sward plots were ca. 32–57% higher at Wagga Wagga and ca. 60–164% at Tumbarumba compared to the spray plots. In contrast, plant parasitic nematodes were ca. 4-fold greater in inter-row sward plots than the spray plots at Wagga Wagga but 3-fold lower at Tumbarumba. The plant parasitic nematode populations were decreased consistently over time for both treatments and soil layers until at the termination of the experiment when its populations were reduced below 100 m −2 in undervine soil in the Tumbarumba vineyard. Therefore, the overall results from this study showed that non-plant parasitic ‘beneficial’ nematodes were increased generally in plots with permanent swards, which in turn suppressed pest nematodes.

Hydrologic properties of grazed perennial swards in semiarid southeastern Kenya

Identification of plant resources that persist under grazing pressure, support desirable levels of production and at the same time protect the grazing environment is central to sustainable livestock production. This study assessed the infiltration capacity and soil loss associated with perennial swards subjected to different levels of utilization using simulated rainfall. The hypothesis was tested that grazed perennial swards have similar hydrologic properties and threshold removal levels below which runoff increases markedly. Infiltration capacity for the perennial swards increased with increasing stubble height before leveling off towards the highest stubble height. A 50% removal of current growth was the upper limit above which runoffs from the swards increased rapidly. Aggregate stability, organic carbon and percent ground plant cover were the most significant attributes that influenced infiltration capacity. Panicum maximum and Enteropogon macrostachyus were the most suitable perennial swards with favourable soil physical properties and infiltration capacities in the study area. The results support the existence of a threshold level of sward stubble height for minimizing runoff.

Aneuploidy in induced autotetraploid populations of Festuca pratensis, Lolium multiflorum, and Lolium perenne III. Performance of plants at different sowing densities in a perennial sward of tetraploid Festuca pratensis

Klinga, K. 1987. Aneuploidy in induced autotetraploid populations of Festuca pratensis, Lolium multiflorum, and Lolium perenne. III. Performance of plants at different sowing densities in a perennial sward of tetraploid Festuca pratensis-Hereditas 106:277–287. Lund, Sweden. ISSN 0018–0661. Received February 6, 1987 The productivity of an induced tetraploid population of Festuca pratensis at different sowing densities displayed a typical yield-density response. There was a positive response in yield with increasing densities only early in the development of the sward. As the time passed, the variations in sowing densities were compensated by an altered growth made by individual plants. The mortality pattern of plants varied among seasons. During the establishing phase of the sward the mortality was not density dependent. The inferior ability of aneuploids to establish in the sward relative to the euploids was diplayed by a higher mortality of aneuploids. As the plants had grown larger, the mortality of plants became density dependent. Competition started to affect the aneuploids earlier in the development of the sward than the euploids, reflected by a differentiated mortality pattern of aneuploids and euploids. The aneuploid frequency in the seed lot was 29.1 %, and in the end of the experiment the aneuploid frequency was reduced to percentages ranging from 7.9% to 15.7%. The lower productivity of the aneuploids affected the yield only at the early stages of the sward development. Later, the surviving aneuploids were too few to influence the total yield.

Aneuploidy in induced autotetraploid populations ofFestuca pratensis, Lolium multiflorum, and Lolium perenne IV. Competitive interactions between euploid and aneuploid plants in a simulated perennial sward of tetraploid Festuca pratensis

Klinga, K. 1987. Aneuploidy in induced autotetraploid populations of Festuca pratensis, Lolium muitiflorum, and Lolium perenne. IV. Competitive interactions between euploid and aneuploid plants in a simulated perennial sward of tetraploid Festuca pratensis. —Hereditas 107 249–256. Lund, Sweden. ISSN 0018–0661. Received August 5,1987 The competitive interactions in dense perennial stands of autotetraploid Fesruca pratensis were investigated by studying the following factors: (a) the persistence of euploid and aneuploid plants in pure stands and in mixtures; (b) the productivity of the persisting euploid and aneuploid plants in pure stands and mixtures; (c) the dry yield per unit area in the different kinds of growing regimes. About 80 % of the original euploid plants in the mixtures and about 50 % in the pure stands were left at the end of the experiment. The persistence of aneuploids did not differ between the two growing regimes. The aneuploid frequency changed from about 30 % to 20 % during the experimental period. In terms of persistence the euploids were better competitors, displayed by the significantly higher persistence in the mixtures. The yielding capacity and the competitive ability of individual euploids in the mixtures exceeded the aneuploids the year of planting and the first summer of the sward development. Later, the yielding capacity did not differ between the two chromosome categories. The negative agressivity values in the last year of the sward indicated a better competitive ability of the aneuploid plants. The presence of aneuploids in the mixed stands did not cause any conspicuous loss of yield. This was displayed by the lack of significant differences in the dry yield per unit area between the two kinds of stands.