Thresholds of economic damage by clover seed weevil (Apion fulvipes Geoff.) and lesser clover leaf weevil (Hypera nigrirostris Fab.) on white clover (Trifolium repens L.) seed crops

Severe reductions in the seed yield of white clover can occur because of feeding by the white clover seed weevil Apion fulvipes and the lesser clover leaf weevil Hypera nigrirostris which together can reduce the seed yield by more than 0·50. From 2002 to 2006 five field experiments were carried out to investigate the relationship between the density of these two weevil species and seed yield of white clover. Damage caused by the weevils was calculated as the difference in the number of weevils and the difference in seed yield between the average of insecticide‐treated and untreated plots. Loss of seed yield was expressed as a proportion of the seed yield in insecticide‐treated plots, which allowed for a comparison between years as yields in insecticide‐treated plots varied. A multiple regression approach was chosen in which proportional loss in seed yield was the response variable and the weevils A. fulvipes and H. nigrirostris were the independent variables. Data obtained from the experiments were used to construct the following threshold model of economic damage:      

The influence of the radiation environment around the node on morphogenesis and growth of white clover (Trifolium repens)

The growth of clonally propagated clover plants ( Trifolium repens ) in the glasshouse was compared with their growth under canopies of Tropaeolum peregonium with or without supplementation from red light emitting diodes (LEDs) directed at the youngest node bearing a fully expanded leaf. The T. peregonium was grown over a net support so that its roots did not meet those of the clover. A similar experiment was set up in a permanent grassland using canopy shade from various grass species ( Holcus lanatus, Lolium perenne and Agrostis stolonifera ) with and without supplementation. The LEDs increased the ratio of red to far red radiation (R/FR) received by the treated node with no apparent increase in photosynthetically active radiation (PAR) during the day.
The morphogenetic effects of canopy shading (notably fewer branched nodes and less well-developed branches) were largely removed by supplementation so that the supplemented plants came to resemble those grown in full daylight, particularly in the glasshouse experiments. The results highlight the Importance of the radiation environment at the base of the canopy in the morphogenetic responses of plants to putative competition, and the data are consistent with the hypothesis that responses are communicated acropetally along the stolon.     

Nitrogen metabolism and milk production in dairy cows fed semi‐restricted amounts of ryegrass–legume silage with birdsfoot trefoil (Lotus corniculatus L.) or white clover (Trifolium repens L.)

In change‐over trials, mid‐lactation dairy cows were fed concentrate‐supplemented, isonitrogenous and isofibrous perennial ryegrass–legume silage diets that satisfied energy requirements but were suboptimal with respect to metabolizable protein supply. Legumes were either birdsfoot trefoil with low levels of condensed tannins (typical for hemiboreal conditions), or white clover. Averaged over two experimental years, birdsfoot trefoil–based silage resulted in lower digestibility (P < 0·001) of dry matter (50 g kg^?1), organic matter (52 g kg^?1), neutral detergent fibre (120 g kg^?1) and nitrogen (24 g kg^?1) and lower rumen total volatile fatty acid concentration (7 mm ; P = 0·009). Milk protein yield was 36 g d^?1 higher with birdsfoot trefoil silage (P = 0·002), while raw milk yield tended to be 0·8 kg d^?1 higher (P = 0·06). Rumen ammonia concentration was similar between diets, but milk urea concentration (P < 0·001), urinary urea excretion (P = 0·002) and faecal‐N proportion (P = 0·001) were higher with birdsfoot trefoil silage. The results suggest that grass–birdsfoot trefoil silage produced in hemiboreal areas exhibits a protein‐sparing effect in dairy rations, despite a low condensed tannin content that is further diluted by companion grasses and ration concentrate proportion.     

Effect of boron on the development of brown rot (Monilinia laxa) on peaches

Requirements of consumers for products with low residues of pesticides have increased the need for alternative disease management practices. The concentration of boron in fruit affects its quality, shelf life and the development of physiological disorders. However, the effect of boron on the susceptibility of peach to fruit rots has not been reported. This study investigated the effect of boron (Power B and Borax) on the development of Monilinia laxa on peaches (cv Andross). Mycelial growth of M. laxa was inhibited on potato dextrose agar supplemented with 750 μg ml⁻¹ of Borax or 1000 μg ml⁻¹ of Power B. The EC 50 values were 107.9 and 522.4 for Borax and Power B respectively. Field investigations showed that the incidence of peach infections by M. laxa was negatively correlated with the content of Boron in the leaves. Post-harvest dipping of peaches in Power B or Borax solution, at concentrations recommended by manufacturer (2 μg ml⁻¹ for Power B and 1 mg ml⁻¹ for Borax), significantly reduced the development of M. laxa. Power B, at rates of 6 μg ml⁻¹, and Borax at rates of 3 mg ml⁻¹ were the most effective in reducing infections by M. laxa. Finally, post-harvest dipping of fruit in Power B or Borax reduced losses of fruit weight and improved fruit firmness one month after storage, showing that boron increased the maintainability of peaches in cold storage. Peaches treated with 6 μg ml⁻¹ Power B or 3 mg ml⁻¹ Borax had the highest flesh firmness and the lowest water losses, while untreated control peaches were the least firm. Generally, Borax was significantly less effective than Power B, but better than the control treatment.     

Interactive Effects of CO2 and O3 on the Growth of Trisetum flavescens and Trifolium pratense Grown in Monoculture or a Bi-Species Mixture

SUMMARY

Golden oat grass (Trisetum flavescens L.) and red clover (Trifolium pratense L.) were grown as monocultures or bi-species mixtures under controlled conditions and exposed to ambient (350 ppm) or elevated (580 ppm) CO₂, with or without addition of O₃ (diel profile with 150 ppb maximum). Shoot biomass measurements after the initial growth and two re-growth periods were used to determine the specific responses of both species, and the difference in the specific response between monocultures and mixtures. T. pratense was much more responsive to CO₂, O₃, and their combination, compared to T. flavescens. In the case of O₃ but not of CO₂, the difference in sensitivity between species was larger in mixture than in monoculture. In contrast to elevated CO₂, O₃ significantly reduced the root:shoot ratio in the mixture, which could explain the increasing negative effect of O₃ on clover with progressing harvests.

The relative CO₂ stimulation of T. pratense and of the cumulative mixture shoot biomass was larger in the presence than in the absence of O₃, which was due to an almost complete protection from O₃ stress by elevated CO₂. In the mixture, the fraction of T. flavescens was small and increased during the experiment; this increase was most pronounced with O3, but any change in mixture biomass was dominated by the response of T. repens.

The results confirm that in grass/legume mixtures legumes are most sensitive to elevated CO₂ and O₃, but the magnitude of specific responses depends on canopy structure and of plant development. Elevated CO₂ minimizes the negative impacts of O₃ stress on above- and below-ground plant growth.     

Effect of plant density on stolon growth and development of contrasting white clover (Trifolium repens) varieties and its influence on the components of seed yield

Plants of two contrasting white clover varieties (cv. Aberystwyth S184 and Olwen) were planted in the field in spring in each of 2 years at four densities (9, 25, 49 and 100 plants m⁻²) in 1-m² plots. The effect of plant density on stolon growth and development and the components of seed yield was subsequently measured.
Stolon growth and development was influenced by plant density, variety and year. At low plant densities both white clover varieties produced longer primary stolons than at higher densities. Plant density, however, had no significant effect on the number of inflorescences at harvest. At the high stolon densities there were significantly fewer reproductive nodes per primary stolon than at the lower plant densities. Plant density did not significantly affect any other seed yield components, but the number of inflorescences at harvest, florets per inflorescence, seed set per floret and 1000-seed weight were all significantly influenced by both variety and year.
The relationship between the vegetative and reproductive growth of white clover is discussed in relation to plant density, variety and climate and the possible role of defoliation managements on inflorescence development.     

Effect of irrigation frequency and planting density on herbage biomass and oil production of thyme (Thymus vulgaris) and hyssop (Hyssopus officinalis)

An experiment was undertaken to determine the herbage biomass and oil production of thyme (Thymus vulgaris Linn.) and hyssop (Hyssopus officinalis Linn.) in 2003 and 2004 in the semi-arid region of Khorasan in Iran. The experiment was a split plot with three irrigation intervals as main plots and three planting densities as subplots, all of which replicated three times. Irrigation intervals consisted of 7, 14, and 21 days for both crops and planting densities of 6.6, 8, and 10 (plants m⁻²) for thyme and 5, 6.6, and 8 (plants m⁻²) for hyssop. Different planting densities were employed by changing planting distances on cultivation rows. Herbage biomass and oil production of shoots, harvested at flowering were measured as annual production of each crop. Irrigation intervals did not change total harvested herbage biomass and oil production of both crops. Averaged across both years of the experiment, thyme produced higher oil than hyssop. Both crops produced higher biomass and oil in the second year of the experiment compared to the first year. While thyme plants biomass and oil production were lower at the highest planting density, hyssop plants showed no response to planting density. Herbage biomass and oil production of hyssop did not show a clear trend in response to interaction of irrigation intervals and planting densities in both years of the experiment. Our results showed that there is a high potential for saving water through longer irrigation intervals (e.g. 14 days) using locally adapted plants in the semi-arid conditions of Khorasan. These crops serve as alternative sources of income in dry years.     

Growth and yield formation of rice (Oryza sativa L.) in the water-saving ground cover rice production system (GCRPS)

A new water-saving ‘Ground Cover Rice Production System’ (GCRPS) was evaluated in 2001 and 2002 near Beijing, North China. Using GCRPS, lowland rice was cultivated without a standing water layer during the entire growth period and plots were irrigated when soil water tension was below 15 kPa (approximately 90% water holding capacity). In order to prevent soil evaporation, the soil surface was covered with 14 μm thick plastic film (GCRPS_Plastic) or mulched with straw (GCRPS_Straw). In a third GCRPS treatment the soil was left uncovered (GCRPS_Bare). These treatments were compared with lowland rice cultivated under traditional paddy conditions (Paddy control). In an additional treatment with bare soil, one aerobic rice variety was cultivated. Compared to Paddy control, only 32–54% of irrigation water was applied in GCRPS treatments. Plants in GCRPS were smaller, developed fewer panicles and had a smaller leaf area index compared to Paddy control. Yield was significantly less in GCRPS_Bare and GCRPS_Straw compared to Paddy control in both years, while yield in GCRPS_Plastic was only 8% less than the Paddy control yield in 2002. Water-use efficiency (WUE, gram grain yield per litre water input) in GCRPS_Plastic was higher (0.35) than in Paddy control (0.23). Grain yield was highly significantly correlated with maximum leaf area index and leaf area index duration. Among yield components, the number of productive tillers had the greatest positive effect on yield, while the number of grains per panicle, thousand-grain weight and harvest index remained almost unaffected. Under uncovered condition, the aerobic rice variety had a significantly higher harvest index (HI), yield, and WUE compared to the lowland rice variety (GCRPS_Bare). The experiment demonstrates that GCRPS has potential to save substantial amounts of water at relatively minor yield penalties, if stress factors such as low soil temperature, water deficit, and nutrient deficiencies during the vegetative growth stage are avoided by suitable management practices.     

Methods of assessing the incidence of Armillaria root rot across viticultural areas and the pathogen's genetic diversity and spatial–temporal pattern in northern Italy

Armillaria mellea (Vahl:Fr.) P. Kumm. is the causal agent of root rots of numerous perennial woody plants, including grapevine. In grapevine, A. mellea infections cause reduced plant vigour, poor grape quality and, in the last stage of the disease, plant death. No post-infection control agents are available for use against this disease. Disease management programmes rely solely on prophylactic measures. Therefore, knowledge of the distribution pattern of the disease over time, disease incidence and actual losses due to the disease across geographical areas is crucial. We evaluated the use of aerial photographs, surveys of growers’ experiences and field assessments to estimate the incidence of Armillaria root rot in a viticultural area (140 ha) situated in the Piana Rotaliana region (Italy). Results of the 4-year assessment were that 25% of the vineyards (36 ha) were infected by Armillaria, 2% of the cultivated vines exhibited disease symptoms and 0.25% of the vines died each autumn. The causal agent was almost exclusively A. mellea but, in two cases, Armillaria gallica was also isolated. The genetic diversity of the Italian population, according to IGS sequencing and somatic incompatibility testing, was very high, suggesting multiple pathogen introduction sites and the slow, vegetative underground spread of the fungus. Fungal clones were found within individual vineyards. Even if, within a particular area, the disease is spreading very slowly and crop losses are limited (one vine out of 400 dies each year), an effective agronomic plan for the prevention of infections should be implemented.     

土壤干旱胁迫对白芥光合器官发育及光合速率的影响

利用旱棚盆栽研究了在土壤干旱胁迫下白芥抗旱和不抗旱品系的单叶面积,单株叶面积、出叶速度、叶绿素含量和和净光合速率。结果表明,在土壤干旱胁迫下不同白品系在不同生育时期的单叶面积、单株叶面积、出叶速度及净光合速率都下降,在一定土壤水分范围内,叶绿素含量随土壤水分的下降而增加,抗旱性强的品系受土壤干旱胁迫的影响较小。     

Effect of irrigation schedule on growth and seed yield of camelina (Camelina sativa L.) in Tarai region of central Himalaya

Camelina(Camelina sativa)has emerged as a potential biofuel crop globally with its suitability even as a jet fuel source with 75–80%less greenhouse gas emissions compared to common petroleum fuels.The crop has originated from Mediterranean region and belongs to Brassicaceae family.DIBER,DRDO has made initial and pioneer efforts in successful introduction of this crop to India and its agro-technology standardization.Being a short duration crop with lesser input requirement,it fits well in the cropping pattern of hilly states of Indian Himalaya.These areas experience fallow land due to shortage of irrigation water for growing other crops.The present study revealed that irrigation at flowering stage is more beneficial.Irrigation at this stage(if only one irrigation is available)exhibited grain yield of 1.004 kg·m^-2which was 21 and 80%higher over pod setting and rosette stage irrigation,respectively.The maximum seed yield was observed under treatment where irrigation was provided at all three crop growth stages(2.044 kg·m^-2).It was 50%higher over T6 treatment(where two irrigations were given at rosette and flowering stage)and 104%higher over T3(where only one irrigation was given at flowering stage).     

Effects of drip irrigation regimes on potato tuber yield and quality under plastic mulch in arid Northwestern China

Field experiments were conducted to study the effects of drip irrigation regimes on potato (Solanum tuberosum L.) growth, tuber yield and quality, and water use efficiency (WUE) when grown under plastic mulch in an arid area of Northwestern China in 2008, 2009 and 2010. The 2008 experiment consisted of a drip irrigation check without plastic mulch and four different drip irrigation frequency treatments with plastic mulch: once every day, once every 2 days, once every 4 days, and once every 8 days. In 2009 and 2010 the drip check treatment without mulch was irrigated at −25 kPa soil matric potential (SMP) during three potato development stages and four different SMP drip irrigation strategies were compared during the potato development stages (using plastic mulch): S1 (−25 kPa SMP during the three development stages), S2 (−25 kPa SMP during tuber initiation and bulking and −35 kPa SMP during maturation), S3 (−25 kPa SMP during tuber initiation and maturation and −35 kPa SMP during bulking), S4 (−35 kPa SMP during the three development stages). Plastic mulch negatively affected tuber yield, WUE, and tuber quality. In the presence of plastic mulch, tuber yield, specific gravity, starch content, and vitamin C content seemed to be enhanced as the irrigation frequency increased, although the differences were not statistically significant. Irrigation frequency did not affect WUE for potato grown under plastic mulch. Analysis of plant height, tuber yield and WUE showed that a drip irrigation threshold of −35 kPa SMP led to obvious water stress for potato growth in this arid area. Under plastic mulch in 2010, S2 was the optimum drip irrigation regime because of the significantly higher yield than S3 and S4, the highest WUE and significantly firmer tubers than any of the other irrigation regimes tested.     

Long-term effect of tillage systems on soil microbiological,chemical and physical parameters and the incidence of charcoal rot by Macrophomina phaseolina (Tassi) Goid in soybean

A 20-year field experiment was employed with the aim of evaluating the effect of tillage systems on biological, chemical and physical aspects of the soil, and to establish whether there was a correlation of these parameters with the incidence of charcoal rot (Macrophomina phaseolina) of soybean and crop yield. The tillage systems evaluated were direct seeding (DS), DS + scarifier (DS + S), minimum tillage (MT) and conventional tillage (CT). DS presented higher values than CT in culturable total fungi (26.33 × 10⁵ vs. 2.33 × 10⁵ CFU g⁻¹ dry soil), total bacteria (182 × 10⁷ vs. 64 × 10⁷ CFU g⁻¹ dry soil), microbial respiration (0.77 mg CO₂ g⁻¹ week⁻¹ vs. 0.45 mg CO₂ g⁻¹ week⁻¹) and fluorescein diacetate (FDA) hydrolysis (4.17 ug fluorescein g⁻¹ h⁻¹ vs. 1.70 ug fluorescein g⁻¹ h⁻¹ in CT. Fungal and bacterial community fingerprints, by terminal restriction fragment length polymorphism (T-RFLP) analysis, of Intergenic spacer regions of rRNA and 16S rRNA genes, respectively, were influenced by the tillage system. Also FAME (fatty acid methyl ester) profiles showed that microbial community structure in DS and CT was clearly different. DS samples contained significantly higher total microbial biomass than the other tillage treatments, but there were no significant differences in fungal biomass or any consistent trend with respect to stress index. Our results showed that microbial communities were more abundant and active in DS than in CT in response to high nutrient content in soil. Indeed, DS systems presented higher soil OM, total N, K and Ca than CT. Electrical conductivity and aggregate stability (AS) were also improved by DS. Soybean grown in high-quality soil was not affected by charcoal rot, however, under CT, disease incidence in soybean was 54%. These differences were correlated to the higher microbial abundance and activity under DS, the biological component being a key factor determining soil capacity to suppress the soilborne pathogen.     

The effect of tree cover on the biomass and diversity of the herbaceous layer in a Mediterranean dehesa

Mediterranean dehesas are an archetypal example of high nature value farmland in Europe. To better understand the interactions between trees and grasslands in the conservation and management of the dehesa, we measured, over 3 years, the contribution of scattered trees to the diversity and biomass dry‐matter (DM) yield of the herb layer and the relationship between the herb layer (biomass and diversity interaction) and the trees. The study was based on 135 subplots representing four aspects and three distances from fifteen trees selected randomly in a plot within a dehesa in central Spain. The specific questions were the following: (i) To what extent do trees affect biomass of the herbaceous layer? (ii) What is the relationship between herbaceous layer biomass and species diversity under the influence of trees? and (iii) What are the effects of trees and small‐scale topography on the herbaceous diversity? Results differed between years depending on water availability. Legume and forb DM yields were highest at the edge of the tree crown and beyond the canopy. Species richness was positively related to legume DM yield, and both were higher at the bottom of the hillside, especially in dry conditions. Given the importance of tree influence on the biomass and diversity of grasslands, maintaining proper agroforestry management practices for trees and grasslands is important for conserving dehesa diversity and productivity under the conditions of high climatic and soil variability in Mediterranean dehesas.     

Effect of Detarium microcarpum (Dm) and Mucuna flagellipes (Mf) gums on the quality of white bread

Incorporation of Detarium Microcarpum (Dm) and Mucuna flagellipes (Mf) water soluble polysaccharides (gums) at 0.0 to 0.5% levels in wheat flour was studied to evaluate their effect on the rheological properties of wheat flour dough and white bread quality. At all levels of incorporation, there were increases (p 0.05) in water absorption of the dough. Doughs containing gums had higher (p 0.05) mixing tolerance index than the control. Set back viscosities decreased by 4.0 RVU and 9.0 RVU with increased levels of Dm and Mf gum incorporation, respectively. Significantly (p 0.05) higher oven spring occurred in all the gum substituted white bread when compared to the control. The 0.5% gum substituted breads had a significantly (p 0.05) higher sensory score for crumb grain, texture but lower (p<0.05) crumb firmness than the control as determined instrumentally. Textural analysis after 5 days storage revealed that Dm and Mf gums improved moisture retention properties of the bread and reduced crumb firming tendency.     

Relations between summer crops and ground cover legumes in a subtropical environment 2. Effects of sorghum and sunflower on the growth of Vigna trilobata and Medicago scutellata

Vigna trilobata (L.) Verdc. is a low growing legume with potential as a ground cover for controlling soil erosion in cropping lands of the subhumid/semi-arid subtropics of northern Australia. When it was grown beneath sorghum (Sorghum bicolor (L.) Moench) and sunflower (Helianthus annuus L.) crops under well-watered conditions on a vertisol in southern Queensland it decreased their yields by about 20% in the first season. This paper reports the effects of competition from crops sown at a normal dryland density or at half the normal density on its growth.V. trilobata sown in pure stand in October produced 531 g m⁻² of above-ground dry matter, and sown in January produced 323 g m⁻², by the time the grain crops sown at the same time were mature. Yields under mature sorghum sown at the normal density (10 plants m⁻²) in October and January were 38% and 35% respectively of those from pure stands of ground cover sown at the same time. Under sunflower at the normal density (5 plants m⁻²), corresponding values were 42% and 22%. The decrease in dry matter yield attributable to competition for water, nutrients and/or radiation from the main crops was proportional to the decrease in intercepted radiation.V. trilobata responded to shade in several ways, but a substantial increase in specific leaf area, together with some additional partitioning of dry matter to leaf, was sufficient to ensure that its leaf area index under crops was similar to that in pure stands.Seed yields of 116 and 84 g m⁻² were obtained from pure stands of V. trilobata sown in October and January respectively. However, seed yields under crops sown at the normal density were only 4–18% of those measured in pure stands. Seed size was not affected by treatment.We conclude that, under well-watered conditions in southern Queensland, V. trilobata grown as a ground cover under crops of sorghum and sunflower should be able to produce sufficient biomass to decrease soil erosion, and also produce sufficient seed for regeneration in successive seasons. Its growth and suitability are also briefly compared with those of an alternative ground cover legume, Medicago scutellata (L.) Mill. (snail medic).     

The effect of an alternate weed host,hairy nightshade,Solanum sarrachoides (Sendtner) on green peach aphid distribution and Potato leafroll virus incidence in potato fields of the Pacific Northwest

Hairy nightshade, Solanum sarrachoides (Sendtner) is an annual solanaceous weed prevalent in potato farmlands of the Pacific Northwest. S. sarrachoides is also a reservoir for Potato leafroll virus (PLRV) and its most important vector, the green peach aphid, Myzus persicae (Sulzer). Green peach aphids prefer S. sarrachoides than potato, Solanum tuberosum (L.), and produce more nymphs on S. sarrachoides than on potato. Increased green peach aphid preference for S. sarrachoides and greater fecundity on this plant could lead to overcrowding and movement toward neighboring potato plants. To test our hypothesis, field trials were conducted at Kimberly, Idaho during the summers of 2003 and 2004. A row of S. sarrachoides seedlings was planted in the middle of potato plots and naturally occurring green peach aphid populations were monitored weekly on potato plots with and without S. sarrachoides. More aphids were consistently found on S sarrachoides plants than on potato plants. More aphids were found on potato plants in plots with S. sarrachoides plants than without S. sarrachoides. Targeted insecticide applications on S. sarrachoides rows alone reduced the number of aphids on potato plants in those plots, suggesting that insecticide sprays prevented aphid movement from S. sarrachoides to potato. Testing of potato tuber sprouts 90 days after harvest by double antibody sandwich ELISA indicated a greater PLRV infection rate on plots with S. sarrachoides than plots without S. sarrachoides. Therefore, the presence of S. sarrachoides in potato plots will likely increase aphid populations and PLRV incidence on neighboring potato plants.     

Effects of inoculum source and irrigation on black dot disease of potatoes (Colletotrichum coccodes (Wallr.) Hughes) and its development during storage

Summary In 1985 and 1986 plots were planted with seed tubers affected with black dot and with healthy seed inoculated or not with cultures ofColletotrichum coccodes at planting. Half the plots were irrigated from shoot emergence to the end of July. Seed tubers rotted more often when they were diseased than when they were not and rotting was increased by irrigation; by contrast, up to 18 weeks after planting irrigation decreased infection of stem-bases, roots and tubers. Tuber infection, first recorded in July, increased throughout the season and most rapidly from September, when the irrigation applied earlier increased disease. Soil-applied inoculum gave most disease in both years and tubers from healthy seed gave least in 1986 but as much as from diseased seed in 1985. Incidence and severity of black dot increased more during storage at 15°C than at 5°C and only on unwashed tubers.     

山区半山区稻瘟病流行区硅肥的抗病增产效果研究

 在山区半山区缺硅多病(稻瘟病)水田进行了施硅肥效果的研究。7年间多点试验结果,施硅使稻瘟病病情指数下降54.6%.平均增产21.5%.亩增稻谷45.8公斤;试验还表明,在这类水田.因受低洼制约,增氮效果难以期望.但以增硅为基础,增氮效果则可正常发挥,所以提高这类水田供硅能力,是实现增肥(N)增产的基础。据此认为,施用硅肥是提高山区半山区多病水田生产力的一项基本措施。     

Effects of systemic fungal endophytes on the performance of meadow fescue and tall fescue in mixtures with red clover

A symbiosis between grasses and systemic fungal endophytes exists in both natural and agricultural grassland communities. Our objective was to examine the effects of systemic endophytes on the competitive ability of two agronomically important grass species: meadow fescue [Festuca pratensis (Huds.) syn. Schedonorus pratensis (Huds.) P. Beauv] and tall fescue [Festuca arundinacea (Schreb.) syn. Schedonorus phoenix (Scop.)]. Plants of meadow and tall fescue were grown for 48 days in replacement series of interspecific mixture with a legume (red clover, Trifolium pratense L.) in different nutrient environments in a greenhouse. Neither of the grass species gained endophyte‐promoted competitive advantage over red clover in grass–clover mixtures. Endophyte infection increased the growth of meadow fescue monocultures by 89% compared to endophyte‐free monocultures in high‐nutrient soils, but plant competition or the cost of endophyte infection to the meadow fescue decreased the yield in resource‐limited conditions. On average, endophyte‐infected and endophyte‐free meadow fescues produced 0·15 and 0·17 g, and 0·14 and 0·14 g dry biomass per plant in mixtures with red clover in high‐ and low‐nutrient soils respectively. In contrast to meadow fescue, endophyte‐promoted growth of tall fescue monocultures was not detected. Endophyte‐infected and endophyte‐free tall fescue monocultures produced 0·76 and 0·95 g biomass per pot, respectively, in the high‐nutrient environment. Endophyte infection can increase the performance of the host grass, but the positive effects depend on the host species, the species composition and soil nutrient availability.