The re-cultivation of abandoned areas creates weed control problems. The main problems in these areas are perennial weeds, such as Cirsium arvense L. but this perennial deep-rooted plant may have a beneficial effect on the physical properties of compacted soil. In order to study the effect of C. arvense's root system on soil properties, the field experiment and a survey of arable fields were conducted in Estonia. The soil bulk density and penetration resistance were measured from soils covered by C. arvense or spring barley (Hordeum vulgare L.) on compacted and un-compacted soil. The results showed significantly lower penetration resistance and bulk density underneath C. arvense than under barley in both the field experiment and a field survey on arable soils. The shoot mass of C. arvense was less affected than the shoot mass of barley by soil compaction and was caused by C. arvense's better ability to develop its root system in compacted soil. Wheat yield, on soils affected by C. arvense, was increased by 28% on loose soil and 37% on compacted soil. It may be concluded that in areas affected by deep-rooted weed species, such C. arvense, the soil's physical properties will improve at least in the first two years.

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In unserem Internationalen Organischen Stickstoffdauerdüngungsversuch (Anlage 1989) auf einer Fahlerde wurde der Einfluß der verschiedenen Stickstoffdüngungsstufen bei unterschiedlicher organischer Düngung auf den Ertrag und die Qualitätsmerkmale von Kartoffeln, Sommerweizen und Sommergerste untersucht. Die 5-jährigen Resultate des IOSDV zeigen, daß die effektivste Stickstoffdüngung für Kartoffeln bei 120 kg N/ha und für Sommerweizen sowie Sommergerste bei 80 kg N/ha lag. Der Stallmist hatte eine gute direkte aber nur bescheidene Nachwirkung auf Getreide, insbesondere im zweiten Jahr. Die Düngerwirkung durch Rübenblätter und Stroh war deutlich besser im Vergleich zu Stallmist.Die Düngung sowohl mit Mineralstickstoff als auch mit Stroh und Rübenblättern verminderte den Stärkegehalt der Kartoffel, erhöhte aber den Rohprotein-und Nitratgehalt. Der Nitratgehalt in den Knollen hing auch von der Knollengröße ab, wobei er in den großen Knollen kleiner war. Zusammenfassend wurde festgestellt, daß auf den Stärkegehalt der Kartoffeln am stärksten die Jahreswitterung gewirkt hat, dagegen auf die Brauqualität der Gerste die Stickstoffdüngung.Die Stickstoffbilanzen weisen in verschiedenen Düngungsvarianten deutliche Unterschiede auf. In Varianten mit organischer Düngung wurde eine positive N-Bilanz festgestellt, dagegen in den Varianten ohne organische Düngung mit mineralischen Stickstoffgaben bis zu 80 kg N/ha abnehmend negative Stickstoffbilanzen.The field experiment of IOSDV (set up in Tartu in 1989) with the application of mineral nitrogen fertilizer in combination with different forms of organic fertilizer (manure, straw, beet-leaves) during 5 years has yield results about the influence of fertilizers on the yield and its quality for potato, spring wheat and spring barley. The optimum norm of nitrogen fertilizers for potato was 120 kg N/ha, for cereals 80 kg N/ha. It was also found that manure can be replace in the crop rotation by ploughed-in-beet-leaves and straw, since the yield thus obtained exceeded that obtained with the application of manure.Mineral nitrogen fertilizer as well as straw and beet-leaves decreased the potato starch content but increased the content of raw protein and nitrates. The nitrate content of potato depended also on the size of potato tubers, being lower in larger tubers. Summing up, the starch content of potato depended considerably on weather conditions of the year of experiment, while the quality of barley depended mainly on the norm of nitrogen fertilizer. Downloaded by [University North Carolina -Chapel Hill] at 05:58 15 December 2014 98 P. KULDKEPPefa/.---The nitrogen balance of the soil is highly different in various fertilization variants. In all variants of organic fertilizers it is strongly positive. In the variant without organic fertilizer, however, it is negative down on the level of 80 kg N/ha.

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