Long-term management impacts on soil C, N and physical fertility: Part II: Bad Lauchstadt static and extreme FYM experiments

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Abstract

Manure is a source of plant nutrients and can make a valuable contribution to soil organic matter (SOM). Two experimental sites were studied on a Halpic Phaeozem soil near Bad Lauchstadt in Germany. The first experiment, called the static experiment, commenced in 1902. The impact of fresh farmyard manure (FYM) (0, 20 and 30 t ha−1 2 year−1) combined with P, K and N fertiliser application on total organic C (CT), labile C (CL), non-labile C (CNL), total N (NT), mean weight diameter (MWD) and unsaturated hydraulic conductivity (Kunsat) was investigated. The second experiment commenced in 1984 and investigated the effect of extreme rates of fresh FYM applications (0, 50, 100 and 200 t ha−1 year−1) and cropping, or a continuous tilled fallow on the same soil properties. At both sites a nearby grassland site served as a reference. On the static experiment, FYM application increased all C fractions, particularly CL, where application of 30 t ha−1 2 year−1 increased CL by 70% compared with no FYM application. Fertiliser additions to the static experiment had a positive influence on C fractions while NT increased from both FYM and fertiliser application. MWD increased as a result of FYM application, but did not reach that of the grassland site. Both fertiliser and FYM application increased Kunsat (10 mm tension) on the static experiment. In the second experiment application of 200 t ha−1 year−1 of FYM increased concentrations of CL by 173% and of CNL by 80%, compared with no FYM application to make them equivalent to, or greater than the grassland site. A continuously tilled fallow resulted in significant decreases in all C fractions, NT and MWD compared with the cropped site, while Kunsat (10 mm tension) was increased on the 0 and 50 t ha−1 year−1 treatments as a result of a recent tillage. There was no difference in Kunsat between the cropped and the continuous tilled fallow at FYM applications of 100 and 200 t ha−1 year−1. There were similar significant positive correlations of all C fractions and NT with MWD on both experimental sites but the relationships were much stronger on the extreme FYM experiment. Weaker relationships of C fractions and NT with Kunsat (10 mm tension) occurred for the static experimental site but these were not significant for the extreme FYM experimental site. The strongest relationship between C fractions and Kunsat was with CL. This research has shown that applications of FYM can increase SOM and improve soil physical fertility. However, the potential risk of very high rates of FYM on the environment need to be taken into consideration, especially since the application of organic materials to soils is likely to increase in the future.

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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