Phosphor im Grünland – Antrieb der Leguminosen, aber Bremse der Phytodiversität?

In our study we investigated the effect of soil phosphorus (P) status on legume occurrence and on phytodiversity of organically managed permanent grassland sites. Therefore, we realized screenings on 2 m x 2 m plots with a clear spatial differentiation between the functional groups ‘legumes’ and ‘non-legumes’ on five mown pasture sites under organic management in north-eastern Germany. We found no significant difference between the phosphorus content of aboveground biomass of legumes and the associated non-legume group. However, we detected a significant difference between the soil PDL contents of these two groups with lower contents in soils of the legume patches whereas the different P fractions and thus different P availability on the mineral site could not explain the occurrence of legumes. Contrary to reports by many ecologists, we could not confirm a clear relationship between soil phosphorus and species number

Cover crops grown in monoculture and mixed cropping affect soils differently

Cover crops provide various benefits to agricultural soils. The legumes among cover crops may provide fixed nitrogen as nutrient. Other species show high uptake and storage capacity for nitrogen, thus preventing losses as water polluting nitrate or greenhouse effective nitrous oxide. The input of carbon by shoot and root biomass, as well as rhizodeposition and root decay after harvest or mulching increases soil quality e.g. in form of nutrient supply and organic matter buildup. Brassicaceae lack mutualism with mycorrhizal fungi and some species can reduce the number of phytopathogenic nematodes, thus affecting food web structures. However, many benefits provided by single plant species may be affected when these species grow under mixed cropping. In a pot experiment ten typical cover crop species were grown in monoculture: Phacelia tanacetifolia, Brassica rapa var. rapa, Raphanus sativus var. oleiformis, Sinapis alba, Trifolium incarnatum, Vicia villosa, Avena strigosa, Lolium multiforum, Sorghum bicolor x S. sudanense, and Fagopyrum esculentum. These were compared to six mixtures ranging in complexity from two to six species including the classics R. sativus/S. alba, R. sativus/A. strigosa, and the “Landsberger Gemenge”. Six plants per pot grew in two differently textured soils (silty loam, loamy sand) in a greenhouse for 60 days. Plant parameters measured, included shoot and root dry matter, their C and N content, root morphology, plant height as well as chlorophyll content. In the soil, the pH, C-to-N-ratio, inorganic nitrogen, microbial biomass, and abundance of microbial domains were measured. Already plant parameters indicated effects caused by mixed cropping. Height and chlorophyll content of P. tanacetifolia, S. alba, and S. bicolor were higher in monocultures than in mixtures indicating interspecific competition. Furthermore, below-ground biomass of two-species-mixtures containing R. sativus appeared to be higher than those of the corresponding monocultures. While monocultures increased soil pH differently, mixtures showed no significant difference between each other. This study aims to show that the impact on soil by different cover crop species are not necessarily realised the same way under mixed cropping

Nitrogen fixation of selected forage legumes for smallholder farmers in Uganda

Poster for the 18th Nitrogen workshop held in Lisbon, June 30 - July 3, 201

Application methods of tracers for N₂O source determination lead to inhomogeneous distribution in field plots

Source determination of N₂O has often been performed using stable isotope incubation experiments. In situ experiments with isotopic tracers are an important next step. However, the challenge is to distribute the tracers in the field as homogeneously as possible. To examine this, a bromide solution was applied as a stand-in tracer using either a watering can, a sprayer, or syringes to a relatively dry (25% gravimetric moisture content) or wet (30%) silt loam. After 1 h, samples were taken from three soil depths (0-10 cm), and analyzed for their water content and bromide concentration. The application with syringes was unsuccessful due to blocked cannulas. Therefore, further laboratory experiments were conducted with side-port cannulas. Despite a larger calculated gravimetric soil moisture difference with watering can application, more Br- tracer was recovered in the sprayer treatment, probably due to faster transport of Br- through macropore flow in the wetter conditions caused by the watering can treatment. The losses of Br- (33% for the watering can, 28% for the sprayer treatment) are equivalent to potential losses of isotopic tracer solutions. For application of 60 at% ¹⁵NHΚ₄+, this resulted in theoretical enrichments of 44-53 at% in the upper 2.5 cm and 7-48 at% in 5-10 cm. As there was hardly any NO₃- in the soil, extrapolations for ¹⁵NO₃- calculated enrichments were 57-59 at% in the upper 2.5 cm and 26-57 at% in 5-10 cm. Overall, no method, including the side-port cannulas, was able to achieve a homogeneous distribution of the tracer. Future search for optimal tracer application should therefore investigate methods that utilize capillary forces and avoid overhead pressure. We recommend working on rather dry soil when applying tracers, as tracer recovery was larger here. Furthermore, larger amounts of tracer lead to more uniform distributions. Further studies should also investigate the importance of plant surfaces

Trends in global nitrous oxide emissions from animal production systems

Wastes from animal production systems contribute as much as 30-50% to the global N2O emissions from agriculture, but relatively little attention has been given on improving the accuracy of the estimates and on developing mitigation options. This paper discusses trends and uncertainties in global N2O emission from animal waste and discusses possible mitigation strategies, on the basis of literature data and results of simple calculations. Total N2O emissions from animal production systems are estimated at 1.5 Tg. Dung and urine from grazing animals deposited in pastures (41%), indirect sources (27%), animal wastes in stables and storages (19%), application of animal wastes to land (10%) and burning of dung (3%) are the five sources distinguished. Most sensitive factors are N excretion per animal head, the emission factor for grazing animals and that for indirect emissions. Total N2O emissions are related to type and number of animals, N excretion per animal, and the management of animal wastes. Projections by FAO suggest that animal numbers will increase by 40% between 2000 and 2030. Mean N excretion per animal head will probably also increase. These trends combined suggest a strong increase in total N2O emission from animal production systems in the near future, which is opposite to the objectives of the Kyoto Protocol. Improving N use efficiency, combined with anaerobic digestion of animal wastes for bio fuel generation are the most feasible options for mitigation, but these options seem insufficient to reverse the trend of increasing N2O emission. In conclusion, animal production systems are a major and increasing source of N2O in agriculture. The uncertainties in the emission estimates are large, due to the many complexities involved and the lack of accurate data, especially about N excretion and the management of animal wastes in practice. Suggestions are made how to increase the accuracy of the emission estimates and to mitigate N2O emission from animal production systems

Biochar reduces the efficiency of nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) mitigating N2O emissions

Among strategies suggested to decrease agricultural soil N2O losses, the use of nitrification inhibitors such as DMPP (3,4-dimethylpyrazole phosphate) has been proposed. However, the efficiency of DMPP might be affected by soil amendments, such as biochar, which has been shown to reduce N2O emissions. This study evaluated the synergic effect of a woody biochar applied with DMPP on soil N2O emissions. A incubation study was conducted with a silt loam soil and a biochar obtained from Pinus taeda at 500 degrees C. Two biochar rates (0 and 2% (w/w)) and three different nitrogen treatments (unfertilized, fertilized and fertilized + DMPP) were assayed under two contrasting soil water content levels (40% and 80% of water filled pore space (WFPS)) over a 163 day incubation period. Results showed that DMPP reduced N2O emissions by reducing ammonia-oxidizing bacteria (AOB) populations and promoting the last step of denitrification (measured by the ratio nosZI + nosZII/nirS + nirK genes). Biochar mitigated N2O emissions only at 40% WFPS due to a reduction in AOB population. However, when DMPP was applied to the biochar amended soil, a counteracting effect was observed, since the N2O mitigation induced by DMPP was lower than in control soil, demonstrating that this biochar diminishes the efficiency of the DMPP both at low and high soil water contents.This work was funded by the Spanish Government (AGL2015-64582-C3-2-R MINECO/FEDER), by the Basque Government (IT-932-16) and by the European Union (FACCE-CSA no 276610/MIT04-DESIGN-UPVASC, FACCE-CSA no 2814ERA01A and 2814ERA02A). This work is also supported by the USDA/NIFA Interagency Climate Change Grant Proposal number 2014-02114 [Project number 6657-12130-002-08I, Accession number 1003011] under the Multi-Partner Call on Agricultural Greenhouse Gas Research of the FACCE-Joint Program Initiative. Any opinions, findings, or recommendation expressed in this publication are those of the authors and do not necessarily reflect the view of the USDA. MLC was supported by a Ramon y Cajal contract from the Spanish Ministry of Economy and Competitiveness and thanks Fundacion Seneca for financing the project 19281/PI/14

a review

It is well documented that global warming is unequivocal. Dairy production systems are considered as important sources of greenhouse gas emissions; however, little is known about the sensitivity and vulnerability of these production systems themselves to climate warming. This review brings different aspects of dairy cow production in Central Europe into focus, with a holistic approach to emphasize potential future consequences and challenges arising from climate change. With the current understanding of the effects of climate change, it is expected that yield of forage per hectare will be influenced positively, whereas quality will mainly depend on water availability and soil characteristics. Thus, the botanical composition of future grassland should include species that are able to withstand the changing conditions (e.g. lucerne and bird's foot trefoil). Changes in nutrient concentration of forage plants, elevated heat loads and altered feeding patterns of animals may influence rumen physiology. Several promising nutritional strategies are available to lower potential negative impacts of climate change on dairy cow nutrition and performance. Adjustment of feeding and drinking regimes, diet composition and additive supplementation can contribute to the maintenance of adequate dairy cow nutrition and performance. Provision of adequate shade and cooling will reduce the direct effects of heat stress. As estimated genetic parameters are promising, heat stress tolerance as a functional trait may be included into breeding programmes. Indirect effects of global warming on the health and welfare of animals seem to be more complicated and thus are less predictable. As the epidemiology of certain gastrointestinal nematodes and liver fluke is favourably influenced by increased temperature and humidity, relations between climate change and disease dynamics should be followed closely. Under current conditions, climate change associated economic impacts are estimated to be neutral if some form of adaptation is integrated. Therefore, it is essential to establish and adopt mitigation strategies covering available tools from management, nutrition, health and plant and animal breeding to cope with the future consequences of climate change on dairy farming