Soil structure and physical state are the basis of the conditions in which the crops grow. Tillage is an important factor affecting soil physical environment. No or reduced tillage under Nordic conditions often causes deterioration of soil physical condition. The aim of the study is to estimate the soil structure and physical state in the seedbed under different tillage and environmental conditions in Estonia and Lithuania. The study involved conventional (ploughing), reduced (ploughless) and no tillage (direct drilling) treatments. The soil structure in the seedbed prepared for spring crops was estimated using the same equipment and the same methods of assessment. The soil structure was estimated by the structure ratio (K str ) and by the structure index (B str ) which were calculated according to the amount of wet-sieved mature soil. In Estonia, the experiments were carried out on different (Fragi-Stagnic Albeluvisol, Endoeutri-Mollic Cambisol, Endoeutri-Haplic Luvisol, Endosceleti-Mollic Gleysol, Gleyc Albeluvisol and Mollic Gleysol) sandy loam soils during the periods 1995-1997 and 2012-2014. The most favourable level of soil structure was determined in the conventionally tilled (ploughed) plots in Gleyic Albeluvisol, Fragi-Stagnic Albeluvisol and in Endoeutri-Haplic Luvisol. Different tillage under conditions of various soils in Estonia also had a significant impact on soil physical properties (bulk density, water content, field capacity) in the seedbed. In heavier soil (clay loam Endocalcari-Endohypogleyic Cambisol) in Lithuania 2011-2014 the most favourable soil structure level in the seedbed was also obtained using conventional ploughing. The worst seedbed structure in clay loam soil was under no tillage in autumn with a cover crop for winter mulch; however, in this treatment the seedbed contained higher soil water content compared to other tillage systems.
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.
The aim of this study was to compare the influence of conventional tillage (CT) and no tillage (NT) on sandy loam and loamy sand soils in three sites of Estonia: 1) Viljandi county (Gleic Albeluvisol), 2) Valga county (FragiStagnic Albeluvisol) and 3) Pärnu county (Mollic Gleysol). The dry bulk density, gravimetric water content and dehydrogenase activity of the soils were determined in the spring of 2013 and 2014. In addition, a soil density index based on soil dry bulk density differences was introduced. Soil samples were collected from 0-10 and 10-20 cm layers in spring. The no tillage treatment had higher soil dry bulk density than the conventional tillage in Gleic Albeluvisol and Mollic Gleysol, where the no tillage fields had not been ploughed for 10 and 2 years, correspondingly. The index of soil density varied between 0.289-0.511, when compared the no tillage and conventional tillage treatments the lowest values were obtained in Gleic Albeluvisol and Mollic Gleysol. Gravimetric water content was significantly lower 2-5% (p < 0.05) in the conventional than in no tillage treatments. No tillage fields showed higher soil dehydrogenase activity in the upper 0-10 cm layer, conventional tillage treatments had no significant differences between the layers. Soil dehydrogenase activity had significant positive correlation (p < 0.01) with soil gravimetric water content and organic carbon, and negative correlation (p < 0.05) with soil dry bulk density and soil density index.
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