Changes in the content of water-soluble sulphur in the soil after an application of straw and elemental sulphur

The changes in the content of water-soluble sulphur in the soil after the application of straw and elemental sulphur (ES) were explored in a 2-year vegetation pot experiment. The following variants were included in the experiment: 1) unfertilised control; 2) wheat straw; 3) rape straw; 4) ES; 5) wheat straw + ES; 6) rape straw + ES. The two types of straw were applied in a dose of 32 g of dry matter and elemental sulphur was applied in a dose of 0.42 g per pot, i.e. 6 kg of soil. The unsatisfactory C:N ratio in the straw was optimised to 25:1 by adding nitrogen in urea. Soil samples were taken prior to sowing of the model plant (spring wheat in 2005 and white mustard in 2006) and then in regular monthly intervals until harvesting (5 times a year). The content of water-soluble sulphur in the soil was evaluated by multifactorial analysis of variance monitoring the effect of the crop, date of soil sampling, application of straw and elemental sulphur.The contents of water-soluble sulphur differed statistically significantly (P > 0.999) when growing the individual model plants. When growing white mustard in 2006 the amount of available sulphur was by 1/5 higher and could have been partly affected by the warm year 2006, as compared to 2005 when spring wheat was grown. Significant differences (P > 0.999) were also discovered among the dates of soil sampling; higher values were detected before the sowing of model plants, i.e. after incubation in the winter, during vegetation the content of water-soluble sulphur decreased and sulphur showed the significantly highest values at the harvest of model plants. When wheat straw was applied the sulphur content did not increase and this may be associated with the wide C:S ratio, whereas after the application of rape straw the content of water-soluble sulphur increased by one third more than in the unfertilised control. The application of elemental sulphur also significantly increased the amount of water-soluble sulphur in the soil, doubling its content.We can conclude that the content of water-soluble sulphur in the soil was strongly affected by the grown crop in combination with the temperatures of the year, it shows considerable dynamics during vegetation culminating at harvest (early August), it was favourably affected by the application of rape straw and it increased considerably after the application of elemental sulphur.