Long-term management impacts on soil C, N and physical fertility: Part II: Bad Lauchstadt static and extreme FYM experiments
Introduction
Manures have traditionally been accepted as a source of plant nutrients; however, the beneficial soil physical effects have received little attention. The maintenance of optimum soil physical fertility is an important component of soil management, which has only recently been accepted (Haynes and Naidu, 1998). This, combined with the need for disposal of large amounts of organic materials such as manure from intensive livestock industries and sewage sludge, along with the potential for sequestering C in soil, means increased emphasis is being placed on effects of manure and sewage sludge application. Application of manure at agronomic rates has traditionally been used but the need for disposal of large quantities in areas close to intensive livestock industries has meant that, in some places, application rates have increased dramatically. In other areas, where manure is not available, or where only small quantities are available, fertilisers are used to increase crop yields in intensive farming systems.
Increased awareness of greenhouse gas emissions and concerns about global warming has led to increased emphasis on sequestering C in the soil (Follett, 2001). The addition of large amounts of organic materials to the soil, such as manures or sewage sludge, could potentially increase soil C concentrations while the increased yields resulting from fertiliser application can result in increased residue and root additions to the soil organic matter (SOM) pool. Swift (2001) suggested that increased soil C concentration was necessary not only for soil C sequestration, but also to alleviate soil degradation by improving soil structure, nutrient cycling and soil fertility to ensure elevated sustainable agriculture production to feed an increasing world population.
It is critical to maintain and/or improve soil quality to sustain agricultural productivity while ensuring environmental quality for future generations (Reeves, 1997). However, to be able to effectively determine the impacts of manure and fertiliser application, particularly at very high rates, on soil properties, requires experiments where treatments have been carried out over long periods to determine both the agronomic and environmental impact.
This study was undertaken on two different experimental sites at Bad Lauchstadt in Germany. One was the Bad Lauchstatd static experiment, which was established in 1902 and the other site was the extreme farmyard manure (FYM) experiment, which was established in 1984. On the static experiment impact of long-term FYM and fertiliser application on soil C fractions, total N, aggregation and unsaturated hydraulic conductivity were investigated, while on the extreme FYM experiment the effect of very high rates of FYM application and tilled, continuous fallows or crop production on these parameters were also studied. These results were compared with a mown grassland pathway adjacent to the experiments, which had been grassland since at least the commencement of the static experiment in 1902. Correlations of soil C fractions with aggregation and unsaturated hydraulic conductivity, and of NT with aggregation and unsaturated hydraulic conductivity were also investigated.
Section snippets
Materials and methods
The Bad Lauchstatd experiments are located in Germany at longitude 11°53′E and latitude 51°24′N. The soil is a Haplic Phaeozem (USDA classification) consisting of 210 g clay kg−1, 678 g silt kg−1 and 112 g sand kg−1 (British International System). The area has a cool temperate climate with a mean annual temperature of 8.7 °C and an annual rainfall of 484 mm (EuroSOMNET, 2001).
Bad Lauchstadt static experiment
Following 96 years of FYM application CT, CL and CNL increased with increasing FYM application rate (Table 1). Even with 96 years of FYM application CT, CL and CNL were still lower than the grassland reference site. CT, CL and CNL were greater with NPK fertiliser than without (Table 2). The CMI also increased with increasing FYM application and with NPK fertiliser compared to without fertiliser.
There was an increase in NT with application of FYM and with NPK fertiliser application (Table 1,
Soil C fractions
The 47% increase in CT as a result of the highest FYM applications compared with the control during the 96 years of the static experiment was lower than expected. Kirchmann and Gerzabek (1999) reported a 75% increase in CT with 9.5 t ha−1 2 year−1 animal manure for 41 years compared with no fertiliser for the Ultano, long-term experiment in Sweden. Colder climatic conditions in Sweden could have reduced organic matter decomposition resulting in larger increases even though the application rates
Conclusions
Significant impacts of fertiliser additions, FYM application and fallow were observed on soil C fractions, NT, MWD and Kunsat in the 0–100 mm soil layer. FYM application increased all C fractions, particularly the labile fraction, with extreme rates increasing C fractions to the equivalent of, or greater than, the reference grassland site. Fertiliser additions also had a positive influence on C fractions and NT most likely due to the increased crop yields returning more organic materials to the
Acknowledgements
This study would not have been possible without the support and funding supplied by postgraduate scholarships from the Grains Research and Development Corporation and the Australian Institute of Nuclear Science and Engineering. We are particularly grateful for assistance provided by technical staff from Agronomy and Soil Science and Environmental Engineering. We especially acknowledge technical help provided by Leanne Lisle and Judi Kenny.
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