Role of phosphorus as a key component for managing grasslands N-yield and phytodiversity in organic farming
Rolle des Phosphors als Steuerungsgröße des Stickstoffertrages und der Phytodiversität ökologisch bewirtschafteter Dauergrünlandbestände
Autor: Mahnke, B.; Korpat, D.; Erlinghagen, R.; Wrage-Mönnig, N.; Müller, J.
Seite: 1 - 104
Jahr: 2017

Einordung:
Institut: Professur Grünland- und Futterbauwissenschaften

Abstract:
The influence of different soil phosphorus levels on grassland legumes’ presence and performance
was investigated within a study framework consisting of field surveys, field experiments, pot experiments and laboratory analyses at different organic grassland sites. The aim was to achieve a better knowledge about the bivalent nature of phosphorus; a plant macronutrient that is able to promote legumes and thus the nitrogen yield, but may concurrently reduce phytodiversity.
Neither plant available phosphorus contents in the topsoil nor different P fractions could satisfactorily explain presence and distribution patterns of legumes in organically farmed grasslands. We concluded that other erratic factors or uncontrolled environmental conditions besides phosphorus nutrition must be responsible for the small scale spatial distribution of grassland legumes. We could confirm that an increase in plant available topsoil P-content tended to reduce phytodiversity. However, this relationship was weaker than in previous international studies that were not restricted to organically farmed grassland. We attributed this finding to the co-limitation of nitrogen as a characteristic of organic farming, which obviously prevented phosphorus from acting as a strong promotor of competitive species responsible for strong declines in phytodiversity. Thus,
fostering grassland legumes on organic grasslands by moderate P fertilization and preserving phytodiversity must not necessarily be a contradiction. Some P fertilizers were found to be useful to facilitate grassland legumes development and performance. As a result of our field plot experiments, the standard fertilizer “Physalg” can be recommended for a fast resolution of P deficiencies and promotion of legume establishment. The bone char fertilizer supplemented with elemental sulphur
was especially suitable for the long-term stabilisation of grassland legumes in the sward without tending to cause soil P-eutrophication. This property predestines bone char for applications in floristically valuable grasslands with a high biodiversity. The alternative recycling fertilizers “Leachphos” and “AshDec” reached levels of nutritional P efficiency comparable to approved standard fertilizers. However, P effects on dry matter yield of grass/legume mixtures were generally
limited. The interaction of fertilizer x kind of legume sometimes observed can be attributed to the
specific root morphology of the different legume species and the associated P uptake capabilities.

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