Effect of root refuse of liquorice on different characteristics of soil from southern regions of Iran. I. Microbial characteristics

Population increase and increasing demand for food have extended agriculture to troublesome areas such as arid and semi-arid regions in which their soils faced with different problems, e.g., deficiency of organic matter, which has great effects on microbial, chemical, and physical soil properties. Attempts to improve the properties of such soils through soil management practices based on organic residue incorporation and build up of soil organic matter. Root refuse of liquorice is added to soils as a soil amendment in some parts of Iran, but its effects on microbial activities of soils has not been studied yet. The present experiment was conducted to study: a) the decomposition rate of root refuse of liquorice in comparison with those of wheat straw and alfalfa in different soils as a function of incubation time, and b) the effect of application of root refuse of liquorice on bacterial and fungal population of the studies soils. In the first series of experiments, in 24 soil samples of Kerman and Fars provinces from southern region of Iran, the decomposition rate of root refuse of liquorice in comparison with those of wheat straw and alfalfa was investigated by determining the evolved CO2 during an eight-week incubation period. And, in the second series, six soil samples were chosen and root refuse of liquorice was applied at the equivalent rates of 0,10, 20, and 30 tons ha(-1), the samples were incubated under room temperature and moisture content of field capacity for 50 days, and the numbers of bacteria and fungi were counted. The decomposition rate of different organic matters (root refuse of liquorice, wheat straw, and alfalfa) was different in various soils with that of root refuse of liquorice being the slowest. The rate of decomposition of root refuse of liquorice was affected by C:N ratio of the tested soils, and lower C:N ratio was associated with higher microbial activity and population of the soil. Decomposition rate was the highest in first and second weeks, and gradually slowed down and finally became steady. The bacteria and fungi populations increased as the amount of applied root refuse increased.