Soil Management,Soil Functions and Soil Fertility. - Results and Recommendations of an Interdisciplinary Workshop Sponsored by the Robert Bosch Foundation,Stuttgart -

The Robert Bosch Foundation, a non-profit organization for public interests and welfare, has sponsored a series of scientific workshops dealing with modern agriculture and its impacts on soil functions and soil fertility. Most of the participants are experts in their fields and members of the German Soil Science Society. The group after a critical analysis of the present situation made conclusions and recommendations, which have been summarized in seven publications and a special memorandum. This article describes the main topics of these documents and summarizes the recommendations.     

Der Umsatz von Pflanzenwurzeln im Laufe der Vegetationsperiode und dessen Beitrag zur „Bodenatmung”︁

The Turnover of Plant Roots during the Growth Period and its Influence on “Soll Respiration” Mustard and wheat plants were grown under ¹⁴CO₂, their roots being tightly separated from the shoot sphere. Root formation, root respiration, and root decomposition could thus be followed during the plant development by radiometric methods. The total quantity of organic root matter in soil at harvest time turned out to be 20–50% larger than the amount of root residues as determined by ordinary washing procedures. Depending on the plant and duration of the experiment, an additional amount of up to three times more than this remaining root carbon was already mineralized during the vegetation period. Only one fifth of this ¹⁴CO₂-production could be attributed to the respiration of living root tissue, all the remainder seemed to be due to the microbial decomposition of dead roots, root residues and root excretions. Root respiration and root decomposition together produced almost four fifths of the total evolving CO₂-quantity, whilst the contribution from soil organic matter breakdown did not exceed one fourth of it. According to these data, the total rhizo-deposition amounts to 3–4 times as much organic substance than what can be found as root residues at harvest time. This rich supply of readily decomposable organic matter leads to a most intensive turnover in the rhizosphere, which should be of considerable influence on the dynamic processes in soil.     

Denitrification losses from an Inceptisol field treated with mineral fertilizer or sewage sludge

In order to evaluate the climatic and soil variables which control the denitrification processes in the field, measurements of N₂O-losses using the C₂H₂ inhibition technique were carried out in an Inceptisol cropped with spring wheat. The silty sand was amended with mineral fertilizer (120 kg N ha^?1) or additionally with sewage sludge (620 kg total N ha^?1). Soil temperature, moisture, nitrate and available carbon, the release of nitrous oxide (N₂O) from the soil surface as well as the N₂O concentrations along the soil profile were measured from March until November 1985 The N₂O surface fluxes from the inorganically fertilized field were well correlated with those from the sewage sludge amended plots (r = 0.76). Multivariate correlation analyses show that particularly soil moisture and nitrate content had a significant effect on the nitrate respiration. The correlation with the soil water content was more clearly expressed by the N₂O surface fluxes than by the N₂O concentrations of the soil air. The N₂O surface fluxes during 1985 totalled about 3 kg N ha^?1 in the minerally fertilized field. Sewage sludge amendments increased the N₂O evolution by 5 times. Spatial variability was high and the N₂O surface fluxes were not well correlated (r = 0.4) with the N₂O concentrations in the soil atmosphere. These experiments provide the background data for a denitrification model and better knowledge about the variables which have to be considered for its validation.     

The nickel uptake from different soils and its prediction by chemical extractions

The uptake of Ni by 13 plant species was investigated from two soil types containing Ni in different concentrations and forms. Absorption was highest from Nicl₂, less from Ni containing sewage sludge or industrial filter dust, and least from a soil containing geogcnic Ni. The 13 species grown can be classified into four groups differing in Ni uptake and toxicity. The Ni contents in grain and in storage organs were larger than in the vegetative plant parts. The highest Ni contents were found in the roots. Plants grown in pots absorbed more Ni than from the same soils in the field. During consecutive years the Ni availability did not decrease. Only soil extractions with unbuffered salt solutions reflected the availability of pollution-derived Ni sufficiently well.