The influence of the expansion of winter crop proportion in the rotation structure on soil biological activity

The effect of the expansion of the winter crop proportion in the crop rotation structure under conditions of conventional (ploughing) and sustainable (reduced) soil tillage on soil biological properties was investigated on a clay loam Gleyic Cambisol at the Joniskelis Experimental Station of the Lithuanian Research Centre for Agriculture and Forestry over the period 2004-06. The effect of a different proportion of winter crop in the rotation on microbial populations in soil was influenced primarily by the weather conditions during the growing seasons. In different years, the number of ammonificators ranged from 5.68 to 28.37 mln g-1, the number of mineralizators ranged from 8.23 to 37.01mln g-1, fungi from 28.55 to 101.46 thousand g-1 of soil. The soil microbial amount was higher under wetter conditions. The numbers of microbes differed between soil tillage systems and had diverse impact. The number of ammonificators did not differ markedly between the soil tillage treatments; however, the number of microbes in the conventionally tilled plots exceeded that in the sustainable tillage system by 5.57%. The sustainable tillage system was positive for N assimilators and fungi. Increasing the winter crop in the rotation did not exert any strong positive effect on all microbes. Increasing the winter crop proportion was favourable for micromycetes. More bacteria were found in the rotation with 25% of winter crop, more mineral N assimilators were found in the rotation with 25% and 50% of winter crop, and fungi max under 50%, 75% and 100% of winter crop in the rotation.