Monitoring der Auswirkungen einer Umstellung auf den biologischen Landbau (MUBIL II). Abschlussbericht

Summary

Since 2003, a long-term field monitoring of the development of Organic Farming has been performed at the bio-farm “Rutzendorf“ in the Marchfeld region east of Vienna. The overall project focus includes three topics: (1) effects of organic farming on soil and plant characteristics depending on three organic fertilization systems (variant 1: green manure: mulching lucerne; variant 2: green manure plus communal compost; variant 3: farmyard manure: harvesting and removal of lucerne crop and cereal straw) (2) effects of hedges on micro climate, water capacity of the soils and crop performances, (3) analyses and cultivation of existing biotopes and establishment of new biotope structures, effects of biotopes and organic farming on the biodiversity of the farm. In the current phase of the project (MUBIL II, 2006 to March 2009), first effects of the conversion have been confirmed and new developments have occurred.
(1) Soil monitoring in the period 2003 – 2008 has shown that the concentrations of plant available, CAL-extractable P and K pools remained in the range of “sufficient availability”. An investigation on five additional sites has shown that also for sites with long term organic farming (12 – 18 years) a sufficient or even high availability of P and K can be expected. This assumption is supported by the fact that in all studied soils a very large pool of organically bound phosphorous (which becomes plant available due to microbial degradation) has been detected. Measurements of the soil water balance showed that biologically farmed fields had higher soil water contents than conventional fields, especially in dry years. A significant impact of the kind of fertilization was not observed. Lucerne in the crop rotation had a positive influence on soil physical parameters like bulk density, saturated hydraulic conductivity, aggregate stability and the N mineralization potential. The densities and diversities of the soil fauna (oribatid and gamasid mites and springtails) were very low at the onset of the study in 2003. Except for the conventional site, the abundance and species richness of Collembola and Gamasida considerably increased in all organic land use types after an initial lag phase. Generally, the conversion to organic farming had a positive effect on Collembola and Gamasida; however, there was no discernible difference between three manure treatments. It is not yet clear if the resulting large numbers will sustain in the following years.
Compared to the conventional managed field the number of weed species on the permanent plots is clearly higher but no continuous increase over the investigated years was detected. Under lucerne and under field pea the highest species numbers were found. Due to a decrease in numbers during the following years of the crop rotation, no problems for the practice are assumed. The different fertilizers have neither shown an effect on the emergence of weeds nor on the number of seeds. The yield of winter wheat following lucerne was significantly lower in variant 3 because of the removal of lucerne biomass in this system in contrast to the systems with lucerne mulching. No significantly positive effect of a fertilisation with communal compost and farmyard manure on crop yield has been detected. However, interesting results can be found by analysis of all fertilised trials of the last years. Overall, the fertilisation with farmyard manure (system 3) reached tendentiously the highest crop yields. The communal compost fertilisation did not show so constant results because of the lower nitrogen effect of the compost in contrast to the farmyard manure. The yield development of the three organic fertilization systems was confirmed by the results of nutrient and humus balances calculated with the agro software REPRO. The nutritional value of wheat from organic farms has been examined. Based on these results, it is recommended to conduct regular feed analysis, implying crude protein analysis at least, if home-grown grains are fed to livestock on organic farms. Variant 1 achieved the highest average gross margin during the six years period. The assumed costs for the organic manure in variant 2 and 3 could not be covered by higher revenues. The main influence on the level of the gross margin was, among the climatic conditions, the fluctuating prices of the cash crops during the sample period.
(2) Field studies have shown a total sphere of influence of hedgerows in relation to their orientation, permeability and height of about the 15 to 20 fold of the height. Furthermore, available water resulting from precipitation, reduced evapotranspiration due to wind breaks or dislocation of snow has a high impact on (soil) water balance and hence on agriculture at this relatively dry location in Rutzendorf. The impact of the hedgerow lead to reduced water losses and higher soil water contents within a distance of 3 times the barrier height. These positive effects were higher in years with low precipitation amounts. Furthermore a positive effect of a hedge on crop yield in the adjacent field was shown. Yield increases ranged from 9.5 to 23.7 percent depending on the cultivated crop, the temperature and the amount of rain in the period of growth.
(3) Hedges and tree rows on the farm proved to be species-poor and the structure is more and more degenerating. Therefore cultivation measures have been identified to improve the multi-functionality of landscape elements as well as biodiversity. These measures have been mapped in a preservation concept for the biotope structures. Along hedges and between fields 6 m broad “eco-stripes” were established. An increase in species diversity was achieved by sowing authochthonal wild flowers in one part of the stripes. In the other part of the stripes, which was left to natural succession, low diversity was recorded. A total of 139 species of wild bees was recorded in the project area Rutzendorf. The results show high diversity and rare species in five year old “eco-stripes” in the east. The species richness of two year old “eco-stripes” was also high, but only euryeicous species were found. Carabids and hoover flies were accumulated in and alongside the eco-stripes due to their rich blossom supply. By single-plant countings of pea aphids and their antagonists in three different distances of a flowering strip, lower aphid densities were recorded close to the eco-stripe. These could not be attributed to higher beneficial efficacy there. The spatial distribution of arthropod group numbers emphasizes the significance of hedges and eco-stripes for arthropod biodiversity. In 2006-2008, the territories of breeding birds in the research area Rutzendorf were censused using the mapping method. The impoverished breeding bird community was dominated by skylark and pheasant. Diversity and abundance of breeding birds have clearly increased since the beginning of the project in 2003.