Home About us Contact
|
Home About us Contact | ||
|
|
||
Randomized Block Design (randomized + block_design)
Selected AbstractsLagged effects of experimental warming and doubled precipitation on annual and seasonal aboveground biomass production in a tallgrass prairieGLOBAL CHANGE BIOLOGY, Issue 12 2008REBECCA A. SHERRY Abstract Global climate change is expected to result in a greater frequency of extreme weather, which can cause lag effects on aboveground net primary production (ANPP). However, our understanding of lag effects is limited. To explore lag effects following extreme weather, we applied four treatments (control, doubled precipitation, 4 °C warming, and warming plus doubled precipitation) for 1 year in a randomized block design and monitored changes in ecosystem processes for 3 years in an old-field tallgrass prairie in central Oklahoma. Biomass was estimated twice in the pretreatment year, and three times during the treatment and posttreatment years. Total plant biomass was increased by warming in spring of the treatment year and by doubled precipitation in summer. However, double precipitation suppressed fall production. During the following spring, biomass production was significantly suppressed in the formerly warmed plots 2 months after treatments ceased. Nine months after the end of treatments, fall production remained suppressed in double precipitation and warming plus double precipitation treatments. Also, the formerly warmed plots still had a significantly greater proportion of C4 plants, while the warmed plus double precipitation plots retained a high proportion of C3 plants. The lag effects of warming on biomass did not match the temporal patterns of soil nitrogen availability determined by plant root simulator probes, but coincided with warming-induced decreases in available soil moisture in the deepest layers of soil which recovered to the pretreatment pattern approximately 10 months after the treatments ceased. Analyzing the data with an ecosystem model showed that the lagged temporal patterns of effects of warming and precipitation on biomass can be fully explained by warming-induced differences in soil moisture. Thus, both the experimental results and modeling analysis indicate that water availability regulates lag effects of warming on biomass production. [source] Dry matter production, nutritive value and efficiency of nutrient utilization of a complementary forage rotation compared to a grass pasture systemGRASS & FORAGE SCIENCE, Issue 3 2008S. C. Garcia Abstract In pasture-based dairy farming, new sustainable systems that involve the annual dry matter (DM) production of grazed and conserved forage beyond the potential of grazed pasture alone are being sought. The objective of this experiment conducted in Australia was to compare a complementary forage rotation (CFR) for conservation and grazing, comprising an annual sequence of three crops, namely maize (Zea mays L), forage rape (Brassica napus L) and a legume (Persian clover, Trifolium repesinatum L or maple pea, Pisum sativum L), with a pasture [kikuyu grass (Pennisetum clandestinum) over-sown with short-rotation ryegrass (Lolium multiflorum L)] as a pasture control treatment. The experiment was a complete randomized block design with four replicates (,0·7 ha each). Annual dry-matter (DM) yield over the 3 years averaged >42 t ha,1 year,1 for the CFR treatment and >17 t ha,1 year,1 for the pasture treatment. The high DM yield of the CFR treatment resulted from >27 t ha,1 year,1 from maize harvested for silage and >15 t DM ha,1 year,1 utilized by grazing the forage rape and legumes. Total input of nitrogen (N) and water were similar for both treatments, resulting in higher N- and water-use efficiency for the CFR treatment, which was more than twice that for the pasture treatment. Overall, the nutritive value of the pasture treatment was slightly higher than the mean for that of the CFR treatment. The implications of these results are that a highly productive system based on the CFR treatment in conjunction with the use of pasture is achievable. Such a dairy production system in Australia could increase the total supply of feed resources grown on-farm and the efficiency of use of key resources such as N and water. [source] Extensification of grassland use in the Welsh uplands: sheep performance in years 1,6GRASS & FORAGE SCIENCE, Issue 2 2001M. Fothergill An experiment was established in 1991 on a 25-year-old perennial ryegrass/bent (Lolium perenne L./Agrostiscapillaris L.)-dominated pasture in Wales to study the effects of reducing nutrient inputs to previously fertilized upland pasture. The effects of the removal of applications of (1) N (denoted by CaPK) (2) N, P and K (Ca) and (3) N, P, K, and Ca (Nil) were compared with a treatment which received applications of all four nutrients (CaPKN) over a 6-year period (1991,96) in a randomized block design replicated three times. The experiment was managed under a continuous variable stocking regime (ewes and lambs until weaning and ewes thereafter) maintaining a sward surface height of 4·0 cm throughout the grazing season. Although individual liveweight gain of the lambs was unaffected by the treatments, there was a significant reduction (P < 0·05) in total lamb liveweight gain, ewe stocking rate and length of grazing season as a result of the withdrawal of nutrients. Over the 6 years total lamb liveweight gain was reduced by 17%, 32% and 45% and ewe stocking rate by 21%, 36% and 49% on treatments CaPK, Ca and Nil, respectively, compared with treatment CaPKN. The effect of withdrawing nutrient inputs on ewe stocking rate was progressive and by 1996 the Nil input treatment displayed a 63% reduction compared with the CaPKN treatment and this was also coupled with a 21-day reduction in length of the grazing season. During the post-weaning period, ewes from the Nil input treatment recorded a liveweight loss in 1995 and only a modest liveweight gain in 1996. This coupled with significantly lower body condition scores (P < 0·01) of these ewes in the autumn indicated that the Nil input treatment could lead to reductions in reproductive performance. [source] Setting management limits for the production and utilization of herbage for out-of-season grazingGRASS & FORAGE SCIENCE, Issue 1 2000Laidlaw Three experiments were carried out on perennial ryegrass-dominant swards to provide a basis for recommendations for the limits to (a) building up and timing of utilization of a herbage ,bank' for out-of-season grazing and (b) duration and intensity of early spring grazing in the United Kingdom and Ireland. In experiment 1, the effect of regrowth interval (from 7 September, 20 October, 17 November or 15 December) in autumn on herbage accumulation, leaf turnover and on subsequent spring growth was investigated. Swards regrown from early September reached maximum herbage mass (about 3 t ha,1 DM) and leaf lamina content in mid-November, by which time senescence rate exceeded rate of production of new leaves. New leaf production and senescence rates were greater in swards remaining uncut until December than in those cut in October or November. Time of defoliation up to December had no effect on spring herbage mass in the subsequent spring. Defoliating in March reduced herbage mass in late May by less than 20%. Experiment 2 investigated the progress in herbage growth and senescence in swards regrowing from different times in late summer and autumn to produce herbage for utilization beyond the normal grazing season. Treatments in a randomized block design with three replicates were regrowths from 19 July, 8 August, 30 August and 20 September. Based on a lower ceiling of leaf and total herbage mass being reached with progressively later regrowths, beyond which leaf senescence generally exceeded leaf production and herbage mass declined, it was concluded that currently recommended rotation lengths for this period should extend from 3 weeks in late July to 8 weeks for swards previously grazed in mid-September. In both experiments, leaf senescence commenced earlier (by one leaf-age category) than previously published estimates and so brought forward the time at which senescence rates balanced leaf growth rates. In experiment 3, designed to evaluate the effect of daily grazing period and intensity in early spring on herbage regrowth, dairy cows grazed successive plots (replicates) for 2 or 4 h each day at two intensities (target residual heights of 5 or 7 cm) in March to mid-April. Regrowth rate was similar in all treatments including the ungrazed control, despite soil moisture content being relatively high on occasions. Tiller density was significantly reduced in May by grazing plots in early or mid-April. It is concluded that in autumn there are limits to which rotation lengths should be extended to produce herbage for out-of-season grazing owing to attainment of ceiling yields. Although utilization in early spring may reduce herbage availability in spring, out-of-season utilization need not reduce herbage growth rates in early spring. [source] Transgenic virus resistance in cultivated squash affects pollinator behaviourJOURNAL OF APPLIED ECOLOGY, Issue 5 2009Holly R. Prendeville Summary 1.,Two ecological risks associated with the use of transgenic crops are transgene movement into wild populations and effects on non-target organisms, such as pollinators. Despite the importance of pollinators, and their contribution to the global food supply, little is known about how they are affected by transgenic crops. Pollinator preferences affect plant mating patterns; thus understanding the effects of transgenic crops on pollinators will aid in understanding transgene movement. 2.,Honey bee and squash bee visit number and duration were recorded on conventional and transgenic virus-resistant squash Cucurbita pepo planted in a randomized block design. Floral characters were measured to explain differences in pollinator behaviour. The effect of Zucchini Yellow Mosaic Virus infection on pollinator behaviour was also examined. 3.,Honey bees visited female conventional flowers more than female transgenic flowers. Conventional flowers were generally larger with more nectar than transgenic flowers, although floral traits did not account for differences in pollinator visitation. 4.,Squash bees visited male transgenic flowers more than male conventional flowers; squash bees also spent more time in female transgenic flowers than in female conventional flowers. Transgenic flowers were significantly larger with greater amounts of sweeter nectar and they were present in greater number. Floral traits accounted for some of the variation in pollinator visitation. 5.,Squash bee visit number and duration did not differ between virus-infected and healthy plants, but this may be because pollinator behaviour was observed early in the virus infection. 6.,Synthesis and applications. Pollinator behaviour controls patterns of plant mating thus non-target effects of transgenic resistance, such as those observed here, may influence transgene movement into wild populations. These results suggest that transgenic crops should not be planted within the native range of wild relatives because pleiotropic effects may affect crop-wild hybridization and transgene introgression into wild populations. [source] Efficacy of Beauveria bassiana (Bals.) Vuill. against the tarnished plant bug, Lygus lineolaris L., in strawberriesJOURNAL OF APPLIED ENTOMOLOGY, Issue 2 2008R. Sabbahi Abstract Beauveria bassiana has a high insecticidal potential to control the tarnished plant bug, Lygus lineolaris, a significant pest of strawberries. Screening experiments showed that L. lineolaris adults were susceptible to several B. bassiana isolates. Another screening test with Coleomegilla maculata, a natural enemy found in strawberries, was also performed in order to select the isolate having lower entomopathogenic impact on this insect. Based on data obtained from both insect species and on the ecozone origin of the B. bassiana isolates, INRS-IP and INRS-CFL isolates were selected for further experiments. The LC50 values of these two isolates against L. lineolaris adults were 7.8 × 105 and 5.3 × 105 conidia/ml, and average survival time (AST) values were 4.46 and 4.37 days at a concentration of 1 × 108 conidia/ml respectively. Results also indicated that L. lineolaris nymphs are susceptible to the selected isolates. During field experiments, using a randomized block design with four replicates, INRS-IP and INRS-CFL isolates were applied at two rates (1 × 1011 and 1 × 1013 conidia/ha) weekly during a period of 4 weeks. These multiple applications triggered a significant reduction of L. lineolaris nymphal populations in strawberries. Twenty-four days after the first application, a significant difference was observed between the mean population densities of surviving nymphs in all B. bassiana -treated plots (less than one insect per five plants) compared with those in control plots (four insects per five plants). During the field experiment, persistence of insecticidal activity and viability of B. bassiana conidia were also monitored. The results showed the presence of viable and infective conidia up to 6 days after each application on strawberry foliage. Moreover, the multiple applications of B. bassiana at the rate of 1 × 1013 conidia/ha triggered a significant reduction in strawberry fruit injuries induced by L. lineolaris feeding behaviour compared with the control plots. [source] Improvement of Cupressus atlantica Gaussen growth by inoculation with native arbuscular mycorrhizal fungiJOURNAL OF APPLIED MICROBIOLOGY, Issue 3 2007L. Ouahmane Abstract Aims: The study aimed to determine whether inoculation with native arbuscular mycorrhizal (AM) fungi could improve survival and growth of seedlings in degraded soils of Morocco. Methods and Results: Soil samples were collected from the rhizosphere of Cupressus atlantica trees in the N'Fis valley (Haut Atlas, Morocco). AM spores were extracted from the soil, identified and this mixture of native AM fungi was propagated on maize for 12 weeks on a sterilized soil to enrich the fungal inoculum. Then C. atlantica seedlings were inoculated with and without (control) mycorrhizal maize roots, cultured in glasshouse conditions and further, transplanted into the field. The experiment was a randomized block design with one factor and three replication blocks. The results showed that a high AM fungal diversity was associated with C. atlantica; native AM fungi inoculation was very effective on the growth of C. atlantica seedlings in glasshouse conditions and this plant growth stimulation was maintained for 1 year after outplanting. Conclusions: Inoculation of C. atlantica with AM fungi increased growth and survival in greenhouse and field. Significance and Impact of the Study: The data indicate that use of native species of AM fungi may accelerate reforestation of degraded soils. Further studies have to be performed to determine the persistence of these mycorrhizae for a longer period of plantation and to measure the effects of this microbial inoculation on soil biofunctioning. [source] Impact of different sized catheters on pressure-flow studies in women with lower urinary tract symptomsNEUROUROLOGY AND URODYNAMICS, Issue 2 2005Elisabetta Costantini Abstract Aims This study assessed the impact of two catheters on urinary flow in women undergoing a pressure/flow (P/F) study for lower urinary tract symptoms (LUTS). Materials and Methods Women who agreed to undergo urodynamic testing were assigned prospectively to a 7 or 9 Fr catheter in P/F study according to a balanced randomized block design. Exclusion criteria: urinary tract infection, bladder stone or tumor, neuropathy, complete urinary retention, inability to void with catheter in place, free flowmetry volume below 150 ml, and urine volume varying by more than 20% on both free and P/F studies. We compared free flowmetry and P/F flowmetry with a 9 Fr catheter in 126/239 patients (Group A) and with a 7 Fr catheter in 113/239 (Group B). We determined the differences in the P/F results in terms of pre-voided bladder volume, clinical and urodynamic categories, and age groups in the two groups. We compared the diagnosis of obstruction based on Qmax during the P/F study and on Qmax in free uroflowmetry. Results In Groups A and B, the Qmax rate was significantly less (P,<,0.001) in P/F studies. Catheter size did not impact significantly. In patients with cystocele, post-void residue or obstruction flow was reduced more than in the other categories. Qmax diminished with age, by about 15% in women aged 50,60 and by 21% in women over 70 years old. Conclusions Qmax in P/F studies is always reduced independently of catheter size, volume of urine, age, and clinical or urodynamic category. This may have clinical implications when interpreting P/F results and in accurately diagnosing obstruction. © 2004 Wiley-Liss, Inc. [source] Spontaneous recovery of an intensively used grassland after cessation of fertilizingAPPLIED VEGETATION SCIENCE, Issue 4 2009Josef Královec Abstract Questions: (1) Does a fertilized grassland recover in terms of species composition and species richness after stopping the treatment? (2) Which species contributed most to the changes? (3) Is it realistic to rely upon spontaneous recovery in this and similar cases? Location: A large grassland, located in the western part of the Czech Republic in central Europe, latitude 49° 59,, longitude 12° 45,, altitude 750 m a.s.l. Methods: Experimental plots of 2.5 m × 6.0 m were established in the central part of the grassland in 1968 using a randomized block design with the following variants: unfertilized controls, 80, 160, 240 and 320 kg ha,1 of nitrogen, in four or eight (320 kg) replicates. The fertilization regime was stopped in 1989. Phytosociological relevés of 2 m × 4 m in size were made in 1990, 1994, 1996, 1997, 1999, 2003 and 2006. The data were processed by multivariate ordination methods (DCA, CCA). Differences in the number of species per plot were tested by repeated measures anova and Tukey's HSD test. Results: All plots, including controls, exhibited a distinct trajectory through time, reflecting the rates of fertilizer used and generally changing in the same direction. Both time and nutrients significantly influenced the vegetation pattern. Treatments differed significantly in species richness, especially at the beginning of the observation. Differences in later years were less pronounced, thus a convergence between the treatments was evident. Conclusions: During the 16 years after fertilization ceased, the number of species substantially increased not only in the fertilized plots but also in the controls. Species typical of semi-natural grasslands predominantly contributed to the increase. Spontaneous recovery after cessation of fertilizing was relatively efficient, but the fertilized plots were small in size and thus rather easily colonized from outside. For interpretation and extrapolation of results from small experimental plots, it is necessary to consider changes in the broader surroundings. [source] Comparisons of growth and economic performance among monosex and mixed-sex culture of red mud crab (Scylla olivacea Herbst, 1796) in bamboo pens in the tidal flats of mangrove forests, BangladeshAQUACULTURE RESEARCH, Issue 4 2009Mst. Muslima Khatun Abstract An experiment was conducted in a randomized block design to compare growth and economic performance between monosex and mixed-sex culture of red mud crab (Scylla olivacea Herbst, 1796) fed with trash fish at 5,10% body weight per day in the mangrove tidal flat at Burigoaliny Union of Satkhira District, Bangladesh. The experiment had three treatments in triplicate each: (a) all-male culture, (b) all-female culture and (c) mixed-sex culture. Crabs of 80,120 g in size were stocked at a density of 0.5 crab m,2 and cultured for 100 days. Specific growth rates (SGRs) by weight and internal carapace width (ICW) in the all-male culture were significantly higher than those in the all-female culture (P<0.05), while SGRs in the mixed-sex culture showed no significant differences from those in the all-male and all-female culture (P>0.05). No significant differences in final mean body weight, ICW, daily weight gain, survival rate, gross and net yields were found among all the treatments (P>0.05). The area of high water level with mangroves gave significantly better results in terms of feed conversion ratio, survival rate, gross and net yields than the area of low water level (P>0.05). The experiment suggests that the all-female culture in the area of high water level with mangroves could be suitable in developing commercial pen culture of red mud crabs in Bangladesh. [source] | |||||||||||||