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Disturbance Ecology

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Master Thesis

Können Düngung und Mahdzeitpunkt die negativen Auswirkungen erhöhter Niederschlagsvariabilität auf Biomasse und Futterqualität eines extensiv genutzten Grünlandes kompensieren?

Laura Dienstbach (05/2011-05/2011)

Support: Jürgen Kreyling, Anke Jentsch


Climate change is predicted to alter rainfall variability and will likely increase the occurrence of droughts. This might lead to a decrease of yield and quality of crops in German agriculture. It is assumed that adapted land management strategies could mitigate negative effects of increased rainfall variability on yield and forage quality of grassland.

The aim of this study is to examine the compensatory effect of two land management strategies, namely fertilization during drought and a ten day shift of the harvest date, on negative impact of increased rainfall variability.

The multifactorial field experiment EVENT II was conducted in a semi-natural grassland community (Gallio molliginis-Allopecurus pratensis) to analyse the effect of land management strategies interacting with different rainfall variabilities (low - weekly average precipitation, mid - natural rainfall and roof artefact control, high - drought of 42 days; with equal sum of annual rainfall amount) as well as different timing of drought (spring drought and summer drought). The parameters measured were aboveground biomass and forage quality. Forage quality was evaluated analysing the nutritive value by near-infrared reflectance spectroscopy. Significant differences were determined by analyses of variance of a linear mixed models followed by a post-hoc test (Tukey HSD).

Increased rainfall variability decreased aboveground biomass from 697 g m-2 by 110 g m-2 and yield of metabolizable energy. Higher rainfall variability increased crude protein content from 83 g kg-1 by about 10 g kg-1 and content of metabolizable energy and decreased crude fibre content and therefore led to enhanced forage quality. The roof artefact control of the natural rainfall variability showed, that the rainout shelters influenced biomass and forage quality by decreasing the effects between low and high rainfall variability. Quality and aboveground biomass remained unaffected by the applied land management strategies and their combination at higher rainfall variability. Summer drought decreased forage quality in comparison to spring drought by reducing crude protein content by about 15 g kg-1 and aboveground biomass from 590 g m-2 by about 100 g m-2. The applied land management strategies or their combination did therefore not mitigate the negative effects of summer drought on aboveground biomass and forage quality. A higher content of crude protein in forage was however achieved by a delayed harvest date (increase by about 15 g kg-1) and by fertilization during spring drought.

The findings of this study highlight the negative effects of increased rainfall variability and severe drought on yield and forage quality and demonstrate that fertilization or a ten day shift of harvest date did not buffer these effects.

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