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The goal of this research was to study the impact of cut plant residues, returned to or removed from the grassland sward, on the dry-matter yield of swards and on the organic carbon (Corg) concentration of soil. The experiment was carried out during 2004–2008. The variables of the experiment were (i) sward type: turfgrass sward (Festuca rubra rubraandPoa pratensis) and grass–clover sward (Phleum pratense,Lolium perenne, andTrifolium repens) and (ii) treatment of residues: the cut plant residues were returned (RRT) to the plots or removed (RRM) from the plots after the mowing. The fertilizer treatments were as follows: N0P0K0, N80P11K48, N160P22K96, and N400P56K240kg ha−1for the turfgrass sward and N0P0K0and N80P26K50kg ha−1for the grass–clover sward. The Corg and Ntot concentrations in the 20-cm soil layer were measured at the beginning and at the end of the experiment at depths of 0–5 cm and 5–20 cm. Nitrogen was returned as plant residues to the grass–clover sward in treatment N0P0K0at 190 kg ha−1and N80P26K50at 204 kg ha−1and consequently the returned cut plant residues increased the yield by 31% and 22%, respectively. The amount of N returned as residues to turfgrass sward was 31–236 kg ha−1but it had no significant influence on the sward dry-matter yield. During the 5 years of the experiment the Corg content in 0- to 5-cm soil layer of grass–clover sward in treatment RRT increased by 42.9% and in RRM by 32.0% as an average of both fertilization treatments. At the depth 5–20 cm the Corg concentration did not change in treatment RRT, but in treatment RRM with fertilization the Corg concentration decreased by 8.2%. In turfgrass soil the Corg concentration increased in RRT treatment by 21.6% and in treatment RRM by 7.2% during 5 years. In the lower soil layer the concentration of Corg decreased with removal and return of plant residues. The fertilization did not influence the changes of Corg concentration in turfgrass swards soil. [ABSTRACT FROM AUTHOR]

About 60% (678,000 ha) of Estonian arable soils have a deficiency of plant-available magnesium (Mg). The soils formed from dolostone (or dolomite rock) till are considerably richer in Mg than those formed from limestone-rich and noncalcareous tills. Formerly, ground dolostone rock with a high content of mineral dolomite was used only as a soil liming material. Later, dolostone powder (DSP), received in the course of industrial manufacturing of dolostone rubble, was also applied for the mitigation of Mg deficiency in soil. The easily accessible resources of DSP as an industrial waste may also qualify as an Mg fertilizer. It soon became apparent, however, that with the application of DSP to the soil, an excessive quantity of Mg could be accumulated. This Mg surplus in soil destroys the equilibrium in plants' assimilation of nutrition elements and inhibits the normal development of agricultural crops. In our research, the influence of different DSP doses on the yield of red clover (Trifolium pratense L.), lucerne (Medicago sativa L.), barley (Hordeum vulgare L.), wheat (Triticum aestivum L.), and oil rape (Brassica napus L. var. Oleifera subvar. Annua) was studied on arable soils formed from different parent materials. We elucidated from the 2-year experiment the high efficiency of DSP application in increasing the yields of Mg-philic crops such as clover, lucerne, and oil rape. The negative influence of excessive Mg application on crop yields, especially in the first year of DSP application, is more clearly visible on soils that are calcium deficient for plant production. For the amendment of deficiency in Mg acid arable soils, 1-1.5 t ha-1 of DSP should be used every 2 to 3 years. The broad application of industrial-origin DSP is useful from at least three points of view: (1) industrially produced Mg fertilizers may be replaced by a readily available local industrial (mining) by-product, (2) managing costs and territories for the disposal of industrial wastes will be reduced, and (3) it will be possible to attain complex and environmentally friendly utilization of local mineral resources. [ABSTRACT FROM AUTHOR]