A quantitative study of seasonal foraging by the grass harvesting termite,Trinervitermes geminatus (Wasmann), (Isoptera,Nasutitermitinae) in Southern Guinea savanna,Mokwa, Nigeria

Summary Trinervitermes geminatus (Wasmann) harvests standing grass tussocks which are cut into pieces and carried back to the nest. During this activity a certain proportion is left on the soil surface as litter whilst some is ingested. Foraging is mainly accomplished during the dry season (mid-October to the end of April) for periods of 2–4 h daily, either early in the morning, in the evening, or occasionally during both morning and evening. The duration and daily pattern of foraging is partly dependent on temperature, with a lower temperature threshold of 20° C and an upper threshold of 35° C below or above which foraging is restricted.The quantity of grass cut down and carried back to the nest by a population of 737 m^-2 (3.08 g m^-2) was estimated at 60.3 kg ha^-1a^-1 with approximately 18 kg ha^-1a^-1 cut and left as litter. Estimated consumption whilst foraging was approximately 20.4 kg ha^-1a^-1, giving a total consumption of about 81 kg ha^-1a^-1. Compared with a total estimated grass production of 3157 kg ha^-1a^-1 and consumption by cattle of 1404 kg ha^-1a^-1, the quantity of grass removed by T. geminatus, amounting to only 3.1% of the net primary production, did not appear to be economically significant in this locality.     

Nitrogen transfer from arrowleaf clover to ryegrass in field plantings

Arrowleaf clover (Trifolium vesiculosum Savi) and annual ryegrass Lolium multiflorum Lam.) commonly are overseeded in dormant bermudagrass (Cynodon dactylon L. Pers.) sod on coastal plain soils in the southeastern United States. Two field experiments were conducted in consecutive years at different sites to estimate the amount of N transferred from the clover to the annual grass. Nitrogen treatments included 50 kg N ha^-1 as ¹⁵N depleted ammonium nitrate applied in either February or April, and a check (no N applied). Three clippings were made during the cool-season from March to June. In both experiments, less than 5 kg N ha^-1 were transferred from the clover to the grass. Ryegrass yields of dry matter and total N were not increased by growing with clover. Clover growth was typical for the region; average dry matter yield in pure stand was 2,615 kg ha^-1 over the two-year period. Clover in mixed stand fixed between 20 and 60 kg N/ha. Less than 13% of N contained in ryegrass was transferred from arrowleaf clover to ryegrass at any clipping while clover was actively growing. The quantity of N transferred over the entire season was not statistically significant.     

Long- and short-term effects of crop residues on aluminum toxicity,phosphorus availability and growth of pearl millet in an acid sandy soil

Pasture swards containing perennial ryegrass (Lolium perenne L.) alone or with one of five different white clover (Trifolium repens L.) cultivars were examined for production and transfer of fixed nitrogen (N) to grass under dairy cow grazing. Grass-only swards produced 21% less than mixed clover-grass swards during the second year after sowing. Production from grass-only plots under a mowing and clipping removal regime was 44% less than from grass-only plots under grazing. Much of this difference could be attributed to N transfer. In swards without clover, the ryegrass component also decreased in favour of other grasses.The average amount of fixed N in herbage from all clover cultivars was 269 kg N ha^–1 yr^–1. Above-ground transfer of fixed N to grasses (via cow excreta) was estimated at 60 kg N ha^–1 yr^–1. Below-ground transfer of fixed N to grasses was estimated at 70 kg N ha^–1 yr^–1 by ¹⁵N dilution and was similar for all clover cultivars. Thus, about 50% of grass N was met by transfer of fixed N from white clover during the measurement year. Short-term measurements using a ¹⁵N foliar-labelling method indicated that below-ground N transfer was largest during dry summer conditions.     

Herbage response to tree thinning in a Eucalyptus crebra woodland

The effects of a range of tree densities on native herbage (mainly Aristida ramosa, Bothriochloa decipiens and Themeda australis biomass in a Eucalyptus crebra woodland near Kingaroy, Queensland, were investigated between March 1977 and July 1981. Rainfall in this area averages 750 mm year^?1. Initial tree density was 640 trees ha^?1 and this was manipulated using arboricide chemicals to leave plots containing 640, 320, 160, 80 and nil live trees ha^?1. Fires were excluded from the whole area, and half the plots were grazed by cattle. The largest increase in herbage biomass was recorded in the ‘all trees killed’ treatment (nil trees ha^?1), closely followed by the ‘scattered tree’ treatment (80 trees ha^?1). The relationship between tree density and herbage biomass was linear. Recruitment of grass and forb plants, as reflected by changes in density, varied according to treatment. Increased grass recruitment was correlated with cattle grazing, whilst forb recruitment was influenced mainly by tree density.     

Changes of phosphorous fractions under continuous corn production in a temperate clay soil

Limited efficiency of fertilizer P may be improved through an understanding of soil P fraction changes with time. This study examined sequential changes in soil organic P (Po) and inorganic P (Pi) in a Ste. Rosalie clay (Humic Gleysol; fine, mixed, frigid, Typic Humaquept) under continuous corn with and without P fertilization. Soil P was fractionated into Bicarb-Pi and Po, NaOH-1-Pi and Po, HCl-Pi, NaOH-Pi and Po, and Residue-P. In the non-P fertilized plots, soil total extractable Po declined by 14% of the initial value over five years of corn production, whereas soil Pi fractions were unchanged. The losses of soil Po were mainly from NaOH-1-Po. Added fertilizer P increased NaHCO3-Pi and NaOH-1-Pi in plots receiving 44 and 132 kg P ha^-1 yr^-1 and increased Residue-P in plots receiving 132 kg P ha^-1 yr^-1. Although NaOH-1-Po decreased slightly in the plots receiving 44 kg ha^-1 yr^-1 P fertilizer, total soil extractable Po was maintained in P fertilized plots. Mineralization of from 16 to 29 kg P ha^-1 yr^-1 Po was needed to account for soil Po losses. Bicarb-Pi and NaOH-1-Pi appeared to be most important for assessment of soil P fertility changes in long-term fertilized soils.     

Impact of Embryonopsis halticella eaton larvae (Lepidoptera: Yponomeutidae) feeding in Marion Island tussock grassland

Summary Embryonopsis halticella is a brachypterous moth endemic to the Kerguelen Province of sub-Antarctic islands. Its larvae are strictly host-specific grass-borers of the tussock grass Poa cookii, and are the major herbivores on Marion Island. Monthly sampling over one year (1984) on Marion Island showed that E. halticella larvae reach a biomass of 0.222 g m^-2 (dry mass) in P. cookii grassland in summer. In feeding experiments conducted in the laboratory on Marion Island, larvae consumed 0.3 X their own live mass in leaf material daily. Extrapolated consumption rates in the field range from 1 kg ha^-1 month^-1 in winter to 18 kg ha^-1 month^-1 (dry mass) in summer. Total annual consumption, based on leaf feeding only, amounts to 86 kg ha^-1 (dry mass). Significant shifts in diet from foliage to seeds occur during spring, and larvae also consume their own frass and exuviae. It is calculated that E. halticella larvae remove 2.5% of the annual production of Poa cookii in Marion Island tussock grassland.     

Mutualistic functioning of indigenous arbuscular mycorrhizae in spring barley and winter wheat after cessation of long-term phosphate fertilization

 The influence of 23 years of phosphorus (P) application at three annual rates of 0, 17.5 and 52.5 kg ha^–1 on arbuscular mycorrhizal (AM) fungal colonization was studied 10 years after the fertilization treatment ended. The annual application of 52.5 kg ha^–1 was about twice the annual crop P extraction and after 23 years had resulted in a measured increase of 23% in the soil total-P concentration. After 10 and 11 years without fertilization, the total mycorrhizal and arbuscular colonization of the plots previously fertilized at this high rate were still significantly lower than in the plots subjected to the 0 and 17.5 kg ha^–1 rates. Plots previously fertilized annually at the rate of 52.5 kg ha^–1 also had a lower benefit : cost ratio for the symbiosis between AM fungi and plants. Furthermore, P-use efficiency was lower in these plots, although no decrease in total dry matter production was found. Accepted: 13 October 2000     

Effects of white clover (Trifolium repens L.) on plant and soil nitrogen and soil organic matter in mixtures with perennial ryegrass (Lolium perenne L.)

To increase our insight into the above- and belowground N flows in grass and grass-clover swards relations between crop and soil parameters were studied in a cutting trial with perennial ryegrass (Lolium perenne) monocultures and ryegrass–white clover (Trifolium repens) mixtures. The effects of clover cultivar on herbage yield, the amount of clover-derived nitrogen, apparent N transfer to companion grass, dynamics of N and organic matter in the soil were estimated.The grass monocultures had very low DM yields (<2.1 t ha^-1) and a low N concentration in the harvested herbage. During 1992–1995 the annual herbage DM yield in the mixtures ranged from 7.0 to 14.3 t ha^-1, the white clover DM yield from 2.4 to 11.2 t ha^-1 and the mean annual clover content in the herbage DM harvested from 34 to 78%. Mixtures with the large-leaved clover cv. Alice yielded significantly more herbage and clover DM and had a higher clover content than mixtures with small/medium-leaved cvs. Gwenda and Retor. Grass cultivar did not consistently affect yield, botanical composition or soil characteristics.The apparent N₂ fixation was very high, ranging from 150 to 545 kg N ha^-1 in the different mixtures. For each tonne of clover DM in the harvested herbage 49 to 63 kg N was harvested, while the apparent N transfer from clover to grass varied between 55 and 113 kg N ha^-1 year^-1.The net N mineralization rate was lower under monocultures than under mixtures. The C mineralization and the amounts of C and N in active soil organic matter fractions were similar for monocultures and mixtures, but the C:N ratio of the active soil organic matter fractions were higher under grass than under mixtures. This explains the lower N mineralization under grass.     

Soil properties and crop performance on a kaolinitic Alfisol after 15 years of fallow and continuous cultivation

A long-term field experiment was established on a kaolinitic Alfisol in Ibadan, Nigeria, in 1972. The land was cleared manually from secondary forest and used for (i) continuous no-till cropping with maize (Zea mays L.) and maize/cassava (Manihot esculenta Crantz) intercropping, (ii) planted fallow of guinea grass (Panicum maximum Jacq.), leucaena (Leucaena leucocephala de Wit), and pigeon pea (Cajanus cajan Millsp.), and (iii) natural bush regrowth in a randomized complete block design with three replications. At the end of 15 years, the fallow plots were cleared manually and cropped with maize for three years. The chemical and physical soil properties and crop performance of the newly-cleared plots were compared with those under 15 years of continuous cultivation. A total of 26 woody species were identified on the bush regrowth plots. Above-ground biomass accumulation of the bush plots was 157 Mg ha^-1 containing 1316 kg N ha^-1. Guinea grass, leucaena and natural bush regrowth plots had comparable organic C concentrations (approximately 20 g kg^-1) in the surface soil (0 to 10 cm) after 15 years. The organic C concentration in the surface soil under pigeon pea was the lowest (9.5 g kg^-1) among the four fallow treatments. Soil under 15 years of continuous no-till maize with and without residue mulch, respectively, contained approximately half (10 g kg^-1) and a quarter (5.7 g kg^-1) of the organic C under natural bush or guinea grass fallow. The levels of exchangeable Ca, K, Mg and effective cation exchange capacity (ECEC) were lower in the soils under continuous cultivation than in those under natural bush and planted fallow. Soil acidification occurred in soils under continuous cropping as depicted by the lower pH values and greater exchangeable Al and Mn concentrations compared to the fallow plots. Grain yield of maize (3 to 5 Mg ha^-1) without fertilizer application in the plots newly cleared from natural bush, guinea grass and leucaena fallow was comparable with that of continuous no-till maize with residue mulch and chemical fertilizer (N, P, K, Mg, Zn) applications. Among the four fallow treatments, maize grain and stover yields were the lowest in plots cleared from pigeon pea fallow.     

Andropogon gayanus (Gamba Grass) Invasion Increases Fire-mediated Nitrogen Losses in the Tropical Savannas of Northern Australia

Invasive alien grasses can substantially alter fuel loads and fire regimes which could have significant consequences for fire-mediated nutrient losses. The effects of the alien grass Andropogon gayanus Kunth. (Gamba grass) on fire-mediated nutrient losses was evaluated in Australia’s tropical savannas. Losses of macronutrients during fire were determined by comparing the nutrient pools contained in the fine fuel before fire and in the ash after fire. Pre-fire grass nutrient pools were significantly higher in A. gayanus plots than in native grass plots for all nutrients measured (N, P, K, S, Ca, and Mg). Nutrient losses were substantially higher in A. gayanus plots, with 113% higher losses for N, 80% for P, 56% for K, 63 for S, 355% for Ca, and 345% for Mg. However, only losses of N and Mg varied significantly between grass types. A simplified savanna ecosystem nutrient budget estimated that A. gayanus fires led to the net N loss of 20 kg ha⁻¹ y⁻¹. This is a conservative estimate because total fuel loads were relatively low (7.85 t ha⁻¹) for A. gayanus invaded plots leading to a relatively moderate intensity fire (6,408 kW m⁻¹). Higher A. gayanus fuel loads and fire intensities could potentially lead to losses of up to 61.5 kg N ha⁻¹ from the grass fuel. Over the long term, this is likely to lead to depletion of soil nutrients, particularly N, in the already low-fertility tropical savanna soils.     

Banks grass mite (Oligonychus pratensis) abundance on sorghum cultivars with different levels of nitrogen use and metabolism efficiency

Banks grass mite (Oligonychus pratensis (Banks)), abundance was recorded for three years on sorghum (Sorghum bicolor (L.) Moench) cultivars with different levels of nitrogen (N) use and metabolism efficiency. The cultivars included 77CS1, SC630-11E, R6956, and SC325-12. Nitrogen fertilizer was applied to plots containing each cultivar at 0,45, and 180 kg Na ha^–1. Significantly more mites were on plants at 180 kg N ha^–1 than at 0 or 45 kg N ha^–1. The lowest mite densities were recorded on SC325-12, the N-use-inefficient and N-metabolism-efficient cultivar. In July,O. pratensis abundance was statistically equivalent on SC325-12 and on R6956, the other N-metabolism-efficient cultivar. In August, mite densities on R6956 were as high as on 77CS1 and SC630-11E, which are N-metabolism-ineficient cultivars. Mite densities were lower on N-use-inefficient and N-metabolism-efficient sorghum cultivars than on their respective efficiency counterparts. Physiological differences in N-use and metabolism-inefficient cultivars may influence the amount of leaf N plus the amount and form of amino acids and other N-based chemicals in sorghum leaves. These plant chemicals have been shown to influence mite abundance on several hosts, and may have been key to influencing the results of these experiments.     

Effects of removal of organic matter on the productivity of heathlands

Abstract. Effects of milling, mowing and sod cutting on productivity in a Deschampsia grass heath and a Molinia-Deschampsia grass heath were studied from 1977 to 1986. The sum of above-ground biomass, litter and accumulated humified matter (TOM) in both types was ca. 70 ton/ha and the primary productivity 3–5 ton ha^-1yr^-1. Mulching did not affect the annual production. Sod cutting reduced the productivity to 1–2 ton ha^-1yr^-1; on the Molinia-Deschampsia site this reduction lasted for at least a decade, while the Deschampsia heath started to recover from sod cutting soon and increased in productivity again. Annual mowing both with and without removal of hay reduced the production as well, particularly on the Molinia-Deschampsia heath. Lower production was either the result of phosphorus depletion - Molinia-Deschampsia site - or nitrogen depletion - Deschampsia site. In the mowing treatments there was also a depletion of carbohydrate reserves.     

Seasonal dynamics of above‐ and below‐ground biomass and nitrogen partitioning in Miscanthus × giganteus and Panicum virgatum across three growing seasons

The first replicated productivity trials of the C4 perennial grass Miscanthus × giganteus in the United States showed this emerging ligno‐cellulosic bioenergy feedstock to provide remarkably high annual yields. This covered the 5 years after planting, leaving it uncertain if this high productivity could be maintained in the absence of N fertilization. An expected, but until now unsubstantiated, benefit of both species was investment in roots and perennating rhizomes. This study examines for years 5–7 yields, biomass, C and N in shoots, roots, and rhizomes. The mean peak shoot biomass for M. × giganteus in years 5–7 was 46.5 t ha^?1 in October, declining to 38.1 t ha^?1 on completion of senescence and at harvest in December, and 20.7 t ha^?1 declining to 11.3 t ha^?1 for Panicum virgatum. There was no evidence of decline in annual yield with age. Mean rhizome biomass was significantly higher in M. × giganteus at 21.5 t ha^?1 compared to 7.2 t ha^?1 for P. virgatum, whereas root biomass was similar at 5.6–5.9 t ha^?1. M. × giganteus shoots contained 339 kg ha^?1 N in August, declining to 193 kg ha^?1 in December, compared to 168 and 58 kg ha^?1 for P. virgatum. The results suggest substantial remobilization of N to roots and rhizomes, yet still a substantial loss with December harvests. The shoot and rhizome biomass increase of 33.6 t ha^?1 during the 2‐month period between June and August for M. × giganteus corresponds to a solar energy conversion of 4.4% of solar energy into biomass, one of the highest recorded and confirming the remarkable productivity potential of this plant.     

Interactions between perennial ryegrass ( Lolium perenne L.) and white clover (Trifolium repens L.) under contrasting nitrogen availability: productivity,seasonal patterns of species composition,N2 fixation,N transfer and N recovery

Nitrogen (N) fertiliser and clover cultivar choice affect competition and productivity in grass-clover mixtures. Pure stands and mixtures of perennial ryegrass and white clover cultivars with contrasting growth habits were examined. The aim of this work was to study the effect of repetitive nitrogen (N) application and cultivar combination on competition and productivity, N yield in the harvested herbage, N₂ fixation in mixtures and pure stands, and transfer of N from clover to the companion grass. Large-leaved white clover cultivar Alice and small-leaved cv. Gwenda and perennial ryegrass cvs. Barlet (erect) and Heraut (prostrate) were sown in pure stands and as four binary grass-clover mixtures on a sandy soil in 1995. In the mixtures, two levels of N fertiliser were applied: 0 (-N) and 150 and 180 kg ha^-1 y^-1 N (+N) in 1996 and 1997, respectively, while the grass monocultures received three N levels (0, 140/180 and 280/360 kg ha^-1) in 1996 and 1997, respectively. No N was applied to pure clover. The plots were cut five times during 1996 and six times during 1997. Fertiliser N was applied in early spring and after every harvest. The treatments were continued until the summer of 1999. In pure grass, the applied N was effectively recovered. In mixtures, N application affected competition by enhancing grass growth and the overall effect of N application was 17 kg DM per kg N applied in 1996. However, there was no yield response to N fertilizer in 1997, because this was compensated for by a higher clover production in unfertilised mixtures. In 1997, -N mixtures yielded more N than +N mixtures, owing to the higher clover content and N₂ fixation. Large-leaved clover cv. Alice was better able to withstand the negative effect of repetitive N application on clover production in mixtures and increased its proportion during the growing season of the second harvest year. In 1997, mixtures with Alice yielded more N than mixtures with Gwenda, but in pure clover swards, there was no cultivar effect on N yield. Also, during the autumn of 1998 and the spring of 1999, the clover content was highest in mixtures with Alice. Harvested N and apparent N₂ fixation were almost twice as high in 1997 as in 1996. N yield and apparent N₂ fixation were higher in pure clover than in mixtures. In mixtures, the apparent N₂ fixation in 1996 was 142 kg N ha^-1, irrespective of cultivar or N treatment. In 1997, it was on average 337 kg N ha^-1, and higher in -N mixtures and in mixtures with Alice. For each tonne of clover DM in the harvested herbage, 65 and 57 kg N was harvested in 1996 and 1997 in -N mixtures, respectively. The apparent transfer of clover-derived N to grass was on average 29 and 70 kg N ha^-1 yr^-1 in 1996 and 1997, respectively. It was highest in +N mixtures and highest in mixtures with Gwenda in 1997. In contrast to clover, the grass cultivars were very similar in their productivity and seasonal patterns, despite their contrasting growth habits. Seasonal trends in N yield, N transfer and N recovery are discussed in relation to fertilizer application regimes and variation in production patterns in mixtures and pure stands. This revised version was published online in June 2006 with corrections to the Cover Date.     

Phosphorus purification in buffer zones in cold climates

The retention of agricultural P by 10-m wide grass buffers (GBZ) and buffers under natural vegetation (VBZ) was studied for 10 years in southwestern Finland. The results were compared with those from 70-m long plots without buffers (NBZ). The GBZs were mowed but the VBZs were not managed. Surface waters were directed into a collector trench on each plot. Soil samples were taken from the buffers to determine easily soluble P by a Finnish method (0.5 M NH₄-acetate–0.5 M acetic acid, pH 4.6) and by the Olsen method.The highest losses of all P fractions were measured in spring, when the buffer vegetation had not yet started to grow. The mean annual total phosphorus (TP) loss from the GBZ and VBZ plots (0.7 kg ha⁻¹) was 40% lower than the TP loss from the NBZs (1.2 kg ha⁻¹). However, the loss of molybdate-reactive P (RP) was 70% higher from the VBZs than from the other plots. The concentration of Olsen-P was high (55.9 mg l⁻¹) on the soil surface, 0–2 cm, in the VBZs. The high loss of RP from the VBZs was most likely due to P leaching from the soil surface and decaying grass residue on the VBZs in spring.     

Vegetation and litter production in Southern Guinea savanna,Nigeria

Summary This study examines the woody vegetation, annual leaf-fall and annual wood-fall in Southern Guinea savanna near Mokwa, Nigeria. There were 1425±402 (95% limits) trees ha^-1 of which Caesalpiniaceous legumes made up 53%. Annual leaf-fall was 2.387 t ha^-1 a^-1 equivalent to 11,238,932 kcal ha^-1 a^-1 and was highly seasonal, peaking from November to February, with a maximum in January after the annual bush fires. Annual wood-fall was 1.391 t ha^-1 a^-1 equivalent to 7,598,256 kcal ha^-1 a^-1 and was less seasonal but with two peaks, one from January to March after the fires and another from May to July in the rainy season.The litter-fall data currently available from West Africa are reviewed and indicate a negative correlation between litterfall and latitude (P<0.001). Litter production is found to be positively correlated with rainfall (P<0.001) and it is suggested that seasonal distribution of rainfall may also be a factor contributing to the limits of litter production.     

Variations in 15N abundance in a forest fertilization trial: Critical loads of N,N saturation,contamination and effects of revitalization fertilization

¹⁵N abundances of current needles of Norway spruce collected during 23 yrs of a forest fertilization experiment were studied in order to follow ecosystem gains and losses of N. Unlabelled ammonium nitrate at four rates (N0–N3), phosphorus at three rates (P0–P2), and potassium plus other elements including micronutrients at two rates (K0–K1), had been applied to plots in a complete factorial design. Nitrogen had been applied annually at average rates of 0, 34, 68 and 102 kg N ha^-1 yr^-1. Tree growth had responded positively to additions of N, but the response was remarkably more positive to the N2P2K1 treatment. In N1 treatments, δ¹⁵N (‰) declined over time. This was consistent with an earlier study, and should reflect a change in ¹⁵N abundance towards that of fertilizer N (minus discrimination during uptake), which in turn means accretion of most of the N added. As in the earlier study, in which N3 plots lost most of the N added, the present N3 plots showed an increasing δ¹⁵N (‰). This pattern was not significantly affected by additions of P and K plus other elements, although a weak negative effect of P on N accretion was indicated, i.e. there was a tendency δ¹⁵N (‰) to be higher when P was added. This, and another recent result based on an N budget, shows that so-called revitalization fertilization may well increase growth of trees, but also promotes losses of N from the ecosystem. As in the previous study, a decline in δ¹⁵N (‰) on control plots provided evidence of contamination. Given a removal of 100 kg N ha^-1 at stem harvest and a leaching of 2 kg N ha^-1 yr^-1, our data on ¹⁵N suggest that a load of 9 kg N ha^-1 yr^-1 would saturate the ecosystem after 100 years. This load is only about twice the annual deposition at the site.     

Symbiotically fixed nitrogen from field- grown white and red clover mixed with ryegrasses at low levels of15N-fertilization

A field study was carried out near Zürich (Switzerland) to determine the yield of symbiotically fixed nitrogen (¹⁵N dilution) from white clover (Trifolium repens L.) grown with perennial ryegrass (Lolium perenne L) and from red clover (Trifolium pratense L.) grown with Italian ryegrass (Lolium multiflorum Lam.). A zero N fertilizer treatment was compared to a 30 kg N/ha per cut regime (90 to 150 kg ha⁻¹ annually). The annual yield of clover N derived from symbiosis averaged 131 kg ha⁻¹ (49 to 227 kg) without N fertilization and 83 kg ha⁻¹ (21 to 173 kg) with 30 kg of fertilizer N ha⁻¹ per cut in the seeding year. Values for the first production year were 308 kg ha⁻¹ (268 to 373 kg) without N fertilization and 232 kg ha⁻¹ (165 to 305 kg) with 30 kg fertilizer N ha⁻¹ per cut. The variation between years was associated mainly with the proportion of clover in the mixtures. Apparent clover-to-grass transfer of fixed N contributed up to 52 kg N ha⁻¹ per year (17 kg N ha⁻¹ on average) to the N yield of the mixtures. Percentage N derived from symbiosis averaged 75% for white and 86% for red clover. These percentages were affected only slightly by supplemental nitrogen, but declined markedly during late summer for white clover. It is concluded that the annual yield of symbiotically fixed N from clover/grass mixtures can be very high, provided that the proportion of clover in the mixtures exceeds 50% of total dry mass yield.     

Effect of typhoon disturbance on fine litterfall and related nutrient input in a subtropical forest on Okinawa Island, Japan

Typhoons are frequent on Okinawa Island, southwestern Japan. The effects of typhoon disturbance on the patterns of fine litterfall and related nutrient inputs in a subtropical evergreen broad-leaved forest were studied over 5 years from May 1996 to April 2001. Annual fine litterfall averaged 7558 kg ha⁻¹ (range from 6188 to 9439 kg ha⁻¹) for six sampling plots over 5 years, which differed significantly among years (p<0.001) but not among plots (p=0.122). A seasonal maximum was most evident for leaf litter component. Woody litter fell more irregularly through the year, and peak fall varied with typhoon and windstorm. The mean ratio of annual litterfall mass of sexual organs to leaves was 0.06, much lower than that in other tropical and subtropical rain forests. Nutrient concentrations varied in litterfall components, but were not significantly different among plots. The lowest concentrations of N and P in leaf litter were observed in March, which is also the month with the greatest leaf fall. However, the highest concentrations were recorded in typhoon season. Nitrogen and P concentrations were 34% and 106% greater in the green leaves that fell during typhoons than in senescent leaves. Mean nutrient inputs by litterfall were: N 83, P 3.2, K 25, Ca 71, Mg 19, Al 12, Na 10, Fe 0.86 and Mn 3.9 kg ha⁻¹ yr⁻¹, and differed significantly among years for all elements (p<0.0005) and among plots only for K (p<0.05) and Mn (p<0.0001). Typhoon disturbance strongly affected annual fine litterfall and related nutrient inputs, which contributed an average of 30% of the annual litterfall mass, and from 30% to 39% (for different nutrient elements) of annual total nutrient inputs. The results from this study suggest that typhoon-driven maintenance of rapid cycling of P and N and their high availability in soil appears to be an important mechanism to maintain productivity in the subtropical forest on Okinawa Island.     

Nitrogen uptake in a Norway spruce stand following ammonium sulphate application,fertigation, irrigation,drought and nitrogen-free-fertilisation

The above-ground accumulation of N,N uptake and litter quality resulting from improved or deteriorated availability of water and nutrients in a 25 year old Norway spruce stand in SW Sweden (as part of the Skogaby project) is presented. Treatment include irrigation; artificial drought; ammonium sulphate addition; N-free-fertilisation and irrigation with liquid fertilisers including a complete set of nutrients according to the Ingested principle (fertigation). At start of the experiment the stand contained 86.5 t dry mass and 352 kg N ha⁻¹. The following three years the annual N uptake in untreated trees was 32 kg N ha⁻¹ to be compared with the annual N throughfall of 17 kg ha⁻¹. Simultaneously, the treatment with ammonium sulphate and liquid fertilisation resulted in 48 and 56 kg ha⁻¹ y⁻¹, respectively, in treatment specific N-uptake following an application of 100 kg N ha⁻¹ y⁻¹. Addition of a N-free fertiliser resulted in improved N-uptake by 19 kg N ha⁻¹ y⁻¹ and irrigation by 10 kg N ha⁻¹ y⁻¹, compared to control. A linear relation between total above-ground dry mass production and N-uptake was found for trees growing with similar water availability. Dry mass production increased with increased water availability given the same N-uptake. It is concluded that the studied stand this far is not N saturated', as N fertilisation resulted in both increased N uptake and increased growth. Addition of a N-free-fertiliser resulted in increased uptake of N compared to the control, indicating an increased mineralisation rate or uptake capacity of the root system. The linear relation between N uptake and biomass production shows that at this study site N is a highly limiting factor for growth.