1,720,991 research outputs found
Establishment and Early Yield Development of Five Possible Alternatives to Trifolium repens as a Grassland Legume
No full textThe performance of Trifolium repens as the main grassland legume in temperate climates may decrease under climate change due to more frequent water shortages. This calls for alternative legumes with agronomic potential. We examined germination rates, establishment, winter tolerance and yield potential of Medicago lupulina, Medicago falcata, Lotus corniculatus, Lotus uliginosus and Onobrychis viciifolia both in monoculture and in mixture with Lolium perenne in a two-year container experiment. Germination and establishment of all alternative legumes were comparable to T. repens except of M. falcata with a retarded initial development. L. uliginosus was the only species with an insufficient winter tolerance. In pure stands M. lupulina and L. corniculatus showed a yield potential almost as high as of T. repens. However, their performance in mixture with L. perenne was lower than T. repens. This has to be considered with the choice of less competitive grass partner species when designing seed mixtures
Diversity and functional groups
No full textIn productive agricultural grasslands the relative importance of species identity, species richness and functional group composition for production and yield stability is not clear. We, therefore, tested diversity effects in mixtures of five productive species common in temperate agricultural grasslands in a greenhouse study: Trifolium repens (legume), Lolium perenne, Dactylis glomerata (grasses) and Plantago lanceolata, Taraxacum officinale agg. (forbs). Diversity levels were (i) monoculture; (ii) all possible three‐species mixtures; and (iii) five‐species mixture. Biomass production increased with greater species richness, an effect that was interpreted as a functional response to a higher proportion of legumes in the mixtures. Species identity and functional composition influenced yield and yield stability in different ways. Larger contents of the legume in mixtures increased yield but decreased yield stability while grasses showed the opposite effect in mixtures. The biomass production of forbs was mostly small in mixtures and yield stability decreased with increasing presence of forbs. In productive agricultural grassland, functional group composition, especially the presence of legumes and grasses, seems to be more important for productivity and yield stability than diversity
Phosphorus, Plant Biodiversity and Climate Change
No full textPhosphorus (P) is a major plant nutrient. Its increasing use as a fertilizer has helped to raise crop and fodder production. However, the global reserves and resources of P are finite, demanding an efficient use of P. Under natural conditions, it is often in limited supply. Plants have developed adaptations to small soil P concentrations. Increased P levels can have unwanted side effects like eutrophication and algal blooms. Besides, P concentrations in the soil have often been found to be negatively correlated with plant diversity. For sustainable agriculture, it is essential to understand 1) adaptations of plants to small P concentrations in soils to maintain production with decreasing P reserves, 2) influences of P on phytodiversity to minimize unwanted effects, and 3) future developments of P and phytodiversity in relation to climate change to adjust agricultural practices. P is essential for the energy and sugar metabolism of plants. As it moves in soils by diffusion only, the geometry of the root system is essential for its uptake. Plants have developed different adaptations for P uptake: e.g., localized or overall increases in the number of roots, the development of cluster roots that increase the root surface area by up to 140 times, exudation of different phosphatases and organic acids in reaction to specific forms of P, or symbiosis with mycorrhiza that may be responsible for up to 75% of the P acquired by plants. Gradual differences in these adaptations decrease interspecific competition and facilitate coexistence. Low P concen trations increase plant diversity by favoring stress-tolerant rather than ruderal species or by restricting the growth of competitive grasses more than that of forbs. According to the niche dimension hypothesis, more limiting resources lead to more coexisting species. Worldwide, P limitation is as relevant for plant production as nitrogen (N) limitation. Thus, P could regulate the size of ecological niches by being the main growth-limiting factor or by being coupled to other limiting resources. Global climate change influences soil P availability. Increasing temperatures tend to increase P mineralization of litter. Furthermore, temperature increases by 5 _ºC have been found to double the colonization of roots by mycorrhiza. Nitrogen mineralization was enhanced by on average 48% by temperature increases of between 0.3 and 6.0 _C. Larger amounts of N stimulate phosphatase exudation and plant P uptake. This could result in increased soil P availability, which is further enhanced by increased P mobilization due to human activities. Such a development would reduce phytodiversity and promote the growth of ruderal, fast-growing species. In the long run, this could cause mining of soil P, which would then again increase plant diversity. However, diversity needs a long time to recover from P additions. Therefore, in sustainable agriculture, increases in soil P relative to other factors limiting plant growth have to be prevented to guarantee large phytodiversity
Response of nitrogen oxide emissions to grazer species and plant species composition in temperate agricultural grassland
No full textAgriculture is an important source of the greenhouse gas nitrous oxide (N2O) and the atmospherically important nitric oxide (NO). We evaluated the effects of different grazers and plant species composition on N2O and NO emissions in temperate grassland. Paddocks were grazed rotationally by either cattle or sheep. Mean N2O emissions were 38.7 μg N2O-N m−2 h−1, mean NO emissions 2.4 μg NO-N m−2 h−1. Cumulative NO-N emissions were larger for sheep- than for cattle-grazed paddocks. Plant species composition was insignificant compared to the effect of grazers on N oxide emissions. In a controlled application experiment, plots with cattle excreta showed larger N2O emissions than plots with sheep excreta, reaching peak emissions of 1921 μg N2O-N m−2 h−1 on cattle urine patches compared to 556 μg N2O-N m−2 h−1 on sheep urine patches, related to different N-inputs per excretion. Peak emissions of dung-treated plots were much smaller. The N2O emission factors were 0.4% for cattle urine, 0.5% for sheep urine, 0.05% for cattle dung and 0.09% for sheep dung. N oxide emissions on the paddock scale were larger for sheep- compared to cattle-grazing, despite larger emissions per cattle excretion. We attributed this to the more even spread of sheep excreta compared to cattle excreta
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