[Influence of straw manuring on the qualitative properties of the organic soil substances of a Lehm-Braunschwarzerde (author's transl)].

It is reported on the influence of a long-term field trial with straw manuring at different terms and different nitrogen fertilization steps on the qualitative properties of the organic soil substance. Straw manuring in autumn increased the carbon content in the soil. Increasing amounts of nitrogen intensified this effect. Straw manuring in spring only with simultaneously applied quantities of 100 and 200 kg N/ha, respectively, brought about an increased content of organic substances in soil. With straw manuring in autumn, fractionation of the organic substance in soil showed a smaller amount of humic acids. Increasing nitrogen addition reduced this amount still more than in the plots with straw manuring in spring. The quota of fulvic acids increased. Therefore, the higher content of organic substances, obtained with straw manuring in autumn, is based on an increase of the pre-stages of humic acids and non-humic matter.