Kurzbeschreibung
(Englisch)
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The aim of the project is to develop a set of soil, plant and environmental indicators for permanent grasslands to assess the effect of different P inputs on soil P availability, the risk of P losses, herbage production (quantity and quality) and on the fate of P derived from manure in the environment. These indicators will be used to propose strategies to limit P inputs in grasslands and the risks of P losses to water. The project will be divided in 4 outputs addressing the effect of P inputs and soil properties i) on the soil and manure phosphate availability to plants (output 1), ii) on the risks of phosphate losses from grassland soils (output 2), and iii) on the yield, botanical composition of grasslands and plant P status (output 3). In the 4th output a method based on the measurement of the natural abundance of 18O in the PO4 groups ( ) will be proposed to trace the fate of P in the soil/manure/plant/water system. Once this method is developed, it will be used in outputs 1 and 2 to quantify the fraction of P in grassland soils and in water that is derived from animal manures. The work will be carried out in collaboration with the Department of Earth Sciences of the ETH, the Agricultural Research Stations ART Reckenholz and ACW Changins, the canton Luzern and with the Group of Animal Nutrition of the ETH. This project contributes directly to the objectives of the working group 3 'Mitigation options' of the COST Action 869.
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Partner und Internationale Organisationen
(Englisch)
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AT, BE, BG, CH, CZ, DE, DK, EE, ES, FI, FR, GR, HU, IE, IL, IT, LT, LU, LV, NL, NO, PL, PT, RO, SE, SI, SK, UK
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Abstract
(Englisch)
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The initial aim of the project was to develop for permanent grasslands a set of soil, plant and environmental indicators to assess the effect of different phosphorus (P) inputs on soil P availability, the risk of P losses, herbage production (quantity and quality) and the fate of P derived from manure in the environment. This aim was reached by analyzing plant nutrient content and soil phosphate availability in permanent grasslands managed intensively, semi-intensively and at low intensity, by analyzing the seasonal dynamics of soil P in a grassland managed at low intensity and by developing a method to measure the isotopic composition of oxygen associated to phosphate in water, soil, plant, and fertilizers and implementing it in intensively used grasslands. The plant P nutrition status was evaluated in the aboveground biomass of grasses, legumes and forbs and related to nitrogen (N) and potassium (K) using four indicators: N:P and K:P ratios, the P nutrition index (PNI) and the P index derived from the diagnosis recommendation integrated system (DRIS P). All indicators differentiated between P fertilized and non-P fertilized treatments. The PNI showed the clearest differentiation between insufficient, sufficient and excessive fertilizer inputs. Soil P availability was evaluated in different depths with four extraction methods: CO2 saturated water, NH4+ acetate EDTA, NH4+ oxalate, and a HCO3- saturated exchange resin (PCO2, PAAE, Pox, and Pres, respectively) and by isotopic exchange to measure the amount of P isotopically exchangeable within 1 minute (E1min). Pres was measured on moist samples, whereas the other analyses were carried out on dry soils. Soil available P measured in the 0-5 cm depth was positively correlated to relative yield, P concentration in plant biomass and PNI. These relationships were modeled by the Mitscherlich function. The best correlations were found for Pres. Based on these soil and plant analyses it was possible to identify situations where low P availability limits plant growth (class: deficient), where an additional P input does not improve plant growth (class: sufficient) and where soil P availability and P plant status are present in excess to plant needs (class: surplus). The seasonal variation of soil available P (Pres) and microbial P (Pmic) was studied in a grassland managed at low intensity submitted to the following treatments: no P input (P0), mineral P fertilization (Pmin) and organic P fertilization (Porg). Pres was highest in Pmin, Pmic was highest in Porg, while both pools were low in P0. Increased Pres and reduced Pmic were observed after dry periods. Increases in Pmic were observed in the three treatments after summer and autumn harvests when plant growth rate was low. The fluxes of P through the microbial biomass were always higher than P uptake in harvested above ground biomass, underpinning the importance of the microbial biomass for P cycling in permanent grasslands. Finally, we evaluated the use of a novel isotopic tool (the isotopic composition of oxygen in phosphate, delta18O-PO4) to trace P movements in the environment and to understand the dynamics of P in the soil/plant system. During the first part of the project, we developed and optimized a novel protocol for phosphate extraction and purification allowing analysis of oxygen isotopes. Animal manure, soil P, river and lake waters, along with soil leachates from an artificial rainfall experiment were then characterized for their delta18O-PO4. The measured isotopic signatures gave a reliable indication on the provenance of P and on biological processes driving P cycle.
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