Mown Grassland Research Articles

Nitrous Oxide Concentrations in the Soil of a Mown Grassland: Comparison of Model Results with Soil Profile Measurements

Nitrous oxide (N2O) concentrations in the soilprofile of a fertilized grassland on the Swiss plateauwere measured at irregular intervals during one year.Air samples were taken from air-permeable tubesinstalled at depths between 2 and 100 cm belowthe surface. Highest concentrations in thetopsoil were observed following precipitationafter fertilization. In the subsoil,concentrations were highest when the soil watercontent fell below about 92% after a wet periodand mineral nitrogen was available from priorfertilization. N2O concentrations in thetopsoil were simulated with the process-basedgrassland ecosystem model PaSim 2.5 (PastureSimulation Model) and compared with measured soilN2O concentrations. The model simulated wellthe concentration peaks after fertilizeradditions and the concentrations in winter. Butthe simulated baseline concentrations during thegrowing season were overestimated. Possiblecauses for this discrepancy are discussed andsuggestions are made to improve the model.

Dispersal and microsite limitation in an abandoned calcareous grassland of the southern prealps

Dispersal limitation is often involved when the species composition of a dry abandoned grassland shows a slow response to resumed regular mowing. A seed-addition experiment, using 32 species which do not belong to the local species pool, was performed on Monte San Giorgio (southern Switzerland) to test whether the low recruitment success was due to dispersal limitation or due to unfavourable microsite conditions. In October 1997, 20 species were individually sown in six 3 × 4 m blocks of a 2 × 2 factorial “partial” split-plot design with treatments of abandonment vs. mowing and undisturbed vs. root-removed soil, this last being applied in small naturally-degradable pots. Moreover, 12 species were sown only in the treatments on undisturbed soil. Seedlings of sown and spontaneously germinating seeds were observed on 16 occasions over one 12-month period. Seeds of 31 out of the 32 species germinated. Twenty-four species showed germination rates higher than 5% and different seasonal germination patterns. Established vegetation, especially the tussocks ofMolinia arundinacea, reduced the quality of microsites for germination. Whereas a few species germinated better under the litter ofMolinia arundinacea, many more germinated better under the more variable microsite conditions of a mown grassland. Only a few seedlings of 25 species out of the 31 germinated species survived until October 1998. Seedling survival was negatively affected by litter, unfavourable weather conditions (frost and dry periods followed by heavy rains) and herbivory (slugs and grasshoppers). Tussocks ofMolinia arundinacea, however, tended to protect seedlings. The poor establishment success of “new” species observed in abandoned meadows on Monte San Giorgio after resumed mowing is due to dispersal and microsite limitations.

Adaptive and inevitable morphological plasticity of three herbaceous species in a multi-species community: field experiment with manipulated nutrients and light

Abstract The knowledge on plant species' morphological plasticity has mostly been gained in laboratory and greenhouse studies, and has hardly ever been verified in the field, where the interactive effects of light and nutrient availability operate in combination with biotic interactions. We studied morphological plasticity of shoot in three herbaceous species with different growth-forms and requirements – Hepatica nobilis, Lathyrus vernus, Sesleria caerulea – in a field experiment, established in an annually mown species-rich grassland. Above- and below-ground resource availability was manipulated by fertilization and additional illumination (using mirrors) in a two-factorial randomized design. The main hypothesis was that fertilization of the presumably non-light-limited grassland community would cause light deficit in the canopy, indicated by adaptive plastic responses in shade tolerant species and inevitable plastic responses in light-demanding species. Plants did not respond to additional illumination in non-fertilized plots, showing that the growth of the studied species in this grassland canopy is rather nutrient than light limited. The three species showed strikingly different patterns of response to manipulation of light availability in fertilized treatment. There, the shade-tolerant Hepatica showed an adaptive plasticity by adjusting its morphology to shadier conditions (e.g. by producing shorter petioles). The light-demanding Sesleria could not make use of the extra nutrients without the additional light resource (its growth being light limited in fertilized plots) and produced more shoot biomass and leaf area only with below-ground as well as above-ground resource addition (inevitable plastic response). In Lathyrus, only the main effects of fertilization and illumination were significant.

Satellite monitoring of changes in improved grassland management

In this study, the satellite monitoring of improved grassland management is discussed. In the satellite images acquired during the grass cutting season, mown grasslands show distinctive reflectance characteristics. Using these characteristics, we have analysed changes in grassland use and grass mowing strategies in a dairy farming region of Japan during the past decade. Our analysis shows that the amount of grazing pasture has decreased in the study site, while the timing of mowing the grass has improved. A ground survey of grassland use and grass mowing time in the study site shows the same tendencies. This agreement indicates that satellite remote sensing is an effective tool for monitoring the status of grassland management.

Effects of cattle slurry and mineral N fertilizer applications on various components of the nitrogen balance of mown grassland

It is essential to establish more accurate N balances for different soil-plant systems in order to improve N use efficiency. In this study the N balance was studied in a poorly drained clayey loam soil under natural grassland supplied with either calcium ammonium nitrate or cattle slurry at two application rates. The aim was to determine the efficiency of the N applied and the factors which affect this efficiency. Mineralization-immobilization of N was calculated by balance between the quantified inputs and outputs of N. As N inputs increased, output via herbage yield was accompanied by an increase in apparent immobilization of N in the soil and by larger losses of N by denitrification. The difference between cattle slurry and N fertilizer was that the slurry behaved as a slow release fertilizer, its supply of mineral N being greater in the periods of time when fertilizer was applied a long time ago. Denitrification losses (up to 17% of the N applied) are suggested to be the main factor to mitigate in order to increase N use efficiency. A decrease in net mineralization (up to 136 kg N ha-1 year-1) was observed which was related to the mineral N application rate. There was evidence to suggest that this decrease was due both to the immobilization of the N applied and to a decrease in the rate of gross mineralization when mineral N was applied. Microbial biomass determinations could not explain the changes in the mineralization-immobilization equilibrium of N because of the great coefficients of variation for this determination (mean value of 18%). Nevertheless, it contributed to verify and explain some of the changes observed in this equilibrium.

Spatial variability of nitrous oxide fluxes in mown and grazed grasslands on a poorly drained clay soil

Fluxes of nitrous oxide (N 2O) were measured in mown and intensively-grazed plots on a slightly-sloping, poorly-drained clay soil, using 144 flux chambers on four consecutive days. We tested the hypotheses that (i) spatial variability of N 2O fluxes is larger in grazed than in mown grassland and (ii) spatial dependency is larger in mown than in grazed grassland. Distributions were approximately log-normal. Fluxes from grazed grassland were larger than those from mown grassland. Multiple linear regression analyses showed weak relationships between N 2O flux and moisture, NH 4 +, NO 3 − and C contents, with less than 15% of the variance in N 2O flux accounted for. Spatial variability was large both on a relatively small scale (less than 6 m) and on a larger scale (10–100 m) and was larger on mown grassland than on grazed grassland. Geostatistics showed that N 2O fluxes were spatially dependent for a lag distance of less than 6 m on mown grassland. On grazed grassland fluxes were spatially independent on a scale of < 6 m. The large spatial variability of N 2O fluxes suggests that even measurement techniques that integrate N 2O fluxes over a large area may be hampered by the large spatial variability of N 2O fluxes.

Nitrous oxide fluxes from grassland in the Netherlands: II. Effects of soil type, nitrogen fertilizer application and grazing

SummaryIntensively managed grasslands are potentially a large source of nitrous oxide (N2O) in the Netherlands because of the large nitrogen (N) input and the fairly wet soil conditions. To quantify the effects of soil type, N‐fertilizer application and grazing on total N2O losses from grassland, fluxes of N2O were measured weekly from unfertilized and mown, N fertilized and mown, and N fertilized and predominantly grazed grassland on a sand soil, a clay soil, and two peat soils during the growing season of 1992.Total N2O losses from unfertilized grassland were 2.5–13.5 times more from the peat soils than from the sand and clay soils. Application of calcium ammonium nitrate fertilizer significantly increased N2O flux on all sites, especially when the soil was wet. The percentage of fertilizer N applied lost to the atmosphere as N2O during the season ranged from 0.5 on the sand soil to 3.9 on one of the peat soils. Total N2O losses were 1.5–2.5 times more from grazed grassland than from mown grassland, probably because of the extra N input from urine and dung. From 1.0 to 7.7% of the calculated total amount of N excreted in urine and dung was emitted as N2O on grazed grassland. The large N2O losses measured from the peat soils, combined with the large proportion of grassland on peat in the Netherlands, mean that these grasslands contribute significantly to the total emission from the country.

Vertical canopy structure of Dutch chalk grasslands in relation to their management

Analysis of leaf canopy overtopping relationships was carried out using a non-destructive point quadrat method followed by a destructive stratified harvest of the above-ground phytomass in Dutch chalk grasslands with different management: summer sheep grazing and annual autumn mowing. The two methods of analysis are compared: e.g. relative leaf overtopping can be recorded by the point quadrat method but it is obscured in vertical vegetation profiles based on stratified phytomass distribution. However the stratified harvest method describes the relationship between canopy phytomass and light microclimate, recorded by measuring Photosynthetically Active Radiation (PAR) at different heights in the vegetation. Plant growth form during peak standing crop is of greater significance than Raunkiaerian life form in determining structure of chalk grassland vegetation. In annually mown grasslands, the tall graminoid growth form, shown by Brachypodium pinnatum, reduces PAR in the lower canopy and suppresses most other growth forms except those which can reach the higher canopy levels, e.g. clumped herbs such as Origanum vulgare. In contrast, grazing can result in a reduction of dominance from the tall graminoids and reduction of the abundance of taller, grazing-sensitive herbs, e.g. clumped and climbing herbs such as Origanum and Lathyrus pratensis, and an increase in grazing-tolerant species, e.g. smaller rosette herb growth forms, e.g. Leontodon hispidus and shorter rhizomatous or stoloniferous graminoids, e.g. Carex flacca and Briza media. Changes in both the overtopping hierarchy at the peak of the growing season and the intensity of overtopping in the course of a growing season are of conclusive importance in determining the relative abundance of species in the vegetation.

Changes in Nitrogen Mineralization, Tissue Nutrient Concentrations and Biomass Compartmentation after Cessation of Fertilizer Application to Mown Grassland

1 Nitrogen mineralization was studied in four grasslands (fields A-D), which had not been fertilized for 2, 6, 19 and 45 years, respectively, thereby forming a chronosequence. Fertilizer application was stopped in these fields in order to restore former species-rich communities characteristic of nutrient-poor conditions. 2 The annual nitrogen mineralization rate was unexpectedly low in field A (124 kg ha(-1) year(-1)) because of the absence of net mineralization during the winter period. This may have been due to high nitrification and subsequent denitrification rates. Winter mineralization was observed in fields B-D where annual mineralization rates were 176, 140 and 61 kg ha(-1) year(-1). The soil total N and C pool sizes (0-10cm) decreased over the chronosequence (from 5110 to 2460 kg ha(-1) and from 71 800 to 29 400 kg ha(-1) for N and C, respectively). The relative nitrification rate (nitrate as a fraction of total mineral N) strongly decreased during the chronosequence (88, 75 54 and 51%, respectively). 3 The seasonal dynamics of the compartmentation of biomass and of tissue nitrogen, phosphorus and potassium concentrations were studied in order to obtain insight into some of the causes and consequences of these changes in nitrogen mineralization. Field B had a high shoot and root production, with high turnover of both fractions. Field C had a low shoot production, but a high root production with high turnover. Field D had a high shoot and rhizome biomass, but within-season turnover was probably low. The peak standing crop in field A was unexpectedly low, but was consistent with the low annual mineralization rate measured in this field. 4 Fine root turnover is assumed to be the main source of the organic material which plants add to the soil in these grasslands. The N concentration of the fine roots generally decreased over the chronosequence, suggesting a decreasing quality of the dead organic matter which the plants added to the soil. There were also clear decreases in shoot phosphorus and potassium concentration during the chronosequence. 5 The amount of regrowth immediately after cutting showed a good correspondence with the nitrogen mineralization rate over the same period, with highest regrowth and mineralization rates observed in the most recently fertilized fields. However, peak standing crop prior to cutting did not correspond to the annual nitrogen mineralization rate. It is suggested that the dominant plant species in field D had more below-ground storage and remobilization and had longer-lived tissues (especially below-ground). This enables the species dominating this field to form a high biomass, despite a very low N mineralization rate.

Long-Term Dynamics of Standing Crop and Species Composition After the Cessation of Fertilizer Application to Mown Grassland

(1) Current agricultural overproduction in Western Europe has led to an increase in the area of unfertilized grassland. This paper reports an experiment where fertilizer application was stopped to try to restore former species-rich vegetation. (2) Standing crop and species composition of three different fields were studied during the first 14 years after cessation of fertilizer application. In two fields on peaty soil a strong decrease in standing crop (from 800 to 300g m-2) was observed but in a field on sandy soil, the initial production of 300g m-2 did not decrease. The deviations from the mean between years were significantly correlated to the potential water surplus in the growing season in this latter field, but not for the two fields on peaty soil. The species composition changed gradually in all fields. (3) In the two fields with decreasing standing crop, species-richness per field and per 4-m2 plot increased markedly during the 14 years. A maximum of forty species was observed after 8 years in the field on sandy soil. (4) Several species reached their maximum cover during these successions. The dynamics of species replacement was described using a Gaussian response model for each species. Species indicating nutrient-poor conditions entered earlier in the successional sequence with cutting twice a year and in the field on sandy soil. The results are discussed with regard to diversity-productivity relationships, nutrient cycling and adaptations of species to nutrient-poor conditions.

A field study of the pattern of local spread of ryegrass mosaic virus in mown grassland

SUMMARYIn a field experiment at Hurley, small areas of old ryegrass sward, known to be infected with ryegrass mosaic virus (RMV) were partially surrounded by newly‐sown Italian ryegrass. The experiment was harvested by mowing on five occasions. Samples of Italian ryegrass taken when it was 11 months old showed a very marked increase in the levels of RMV close to the areas of old sward. Thus, 84% of the Italian ryegrass plants bordering the old sward to the north contained RMV, compared with 63% of plants only 2.7 m away. The corresponding values to the south were 68% and 39%. The much higher values encountered to the north are presumed to be caused by the movement of the mite vector of RMV (Abacarus hystrix) in relation to the prevailing wind.Two different mowers were used, a rotary mower and a reciprocating knife mower. We could demonstrate no increase in the level of RMV as a result of mowing from the infected sward and on to the new sowing and could demonstrate no difference in the infection levels as a result of using the different mowers.We conclude that in mown swards migration by the mite is responsible for all or nearly all of very local spread of RMV.

The Fate of Scabiosa columbaria (Dipsacaceae) Seeds in a Chalk Grassland

Factors reducing the seed population of the facultatively polycarpic perennial small scabious, Scabiosa columbaria L., were studied in a mown Dutch chalk grassland. A major proportion of the seeds produced did not germinate. Pre-dispersal predation in the flower heads caused a decrease of 7% of the seed population. Half of the post-dispersal losses were probably due to seed predation by large herbivores, e.g. mice like long-tailed field mouse, Apodemus sylvaticus L. The other losses may be mainly caused by predation by small invertebrates. The post-dispersal losses were highest in open micro-habitats. but after mowing such differences between micro-habitats abruptly disappeared. The resulting 81% reduction in the seed population agrees with figures found in demographic studies. Therefore, and on the basis of earlier germination experiments, we conclude that the influence of abiotic factors in seed population reduction is limited and that predation is more important.

The productivity of grasslands in England for Oscinella frit (L.) (Chloropidae) and other stem-boring Diptera

Dissections of over 93,000 grass stems obtained by random core-sampling of natural grasslands at a site in Berkshire largely confirm earlier conclusions regarding the associations of different species of dipterous stem borers and grasses. Allowing for the number of stems of each grass species per unit area, the densities of larvae were greatest in Anthoxanum odoratum, Poa and Lolium and lowest in Dactylis glomerata. Oscinella frit (L.) was less abundant than Cetema spp. and Opomyza germinationis (L.); it was not found in D. glomerata but was most abundant in Lolium and Festuca. Sampling showed that overwintering larvae of O. frit suffer at least 50 per cent, mortality between September–December and January–March.Previous studies have largely concentrated on populations in different species of grasses, but it is advantageous to consider the production of O. frit in terms of short (grazed or regularly mown) grasslands and long grasslands (hay fields, uncut commons and rough grazing); comparisons of figures obtained by core-sampling for larvae and emergence traps for adults indicate a production from short grassland and long grassland of about 11 and under 1 overwintered adult per sq. yd., respectively. Having regard to the greater productivity of common leys, dominated by Lolium and Poa, a national average for the first figure would be 15. There is little increase from generation to generation in grassland populations during the year, in contrast with the situation in oats.From tentative estimates of the acreages and productivities of the different sources of O. frit in England and Wales as a whole, it is clear that the majority of the adults of O. frit are produced by grasslands in the spring and summer and by the oat panicles in the autumn, the latter population being much the greater. As O. frit is a migratory insect, such a conclusion is especially significant and indicates that during the autumn the ‘ population pressure ’ in the grasslands will be very different to that during other seasons.