Changes In Soil Organic Matter And Biological Mechanisms Under Conservation Tillage Conditions

The study was carried out on a long-term field experiment set up in 2001 in Dingxi, a typical semiarid rainfed agriculture area on the Western Loess Plateau. The objective of the experiment was to determine the effect of conventional and conservation tillage practices on soil organic carbon(SOM), microbial biomass carbon(MBC),the amounts of microorganism and alkaline phosphatase activities in the soil upper layer of Wheat-Pea double sequence rotation system in 2015 before soewing and after harvest. Research the main biological mechanism of soil organic matter changes in conservation tillage in yellow cotton. Treatments included six types of tillage practices; conventional tillage with straw removed(T), no-till with straw removed(NT), conventional tillage with straw incorporated(TS), no-till with straw retained(NTS), conventional tillage with plastic film mulch(TP) and no-till with plastic mulch(NTP). The main results were as follows:1. The SOM content varied in the 5 types of conservation tillage practices in the 0-30 cm depth. The average SOM content under NTS and TS were significantly higher than T. SOM was significantly increased by 12.02% and 12.01% at sowing and 17.38% and 12.42% at harvest of spring wheat in NTS and TS respectively, compared with T. Similarly, NTS and TS significantly increased SOM by 25.63% and 11.61% at sowing and 30.27%, and 12.61% at harvest of field Pea compared with T. NTS significantly greater than T in all the 3 soil layers measured. However, TS differ significantly compared with T in 0-5cm and 5-10 cm soil layer only. The average SOM content recorded in NT and TP had small effect, which was not significant. The SOM content decreased with increasing depth and between sowing and harvest; NTS and TS were the least.2. MBC results found under NTS and TS was significantly higher than T. MBC increased by 43.23% at sowing and 36.53% at harvest of spring wheat in NTS compared with T. In Pea plots, MBC increased by 66.30% and 44.12% at sowing and harvest, respectively in NTS compared with T. The MBC content in the 0-30 cm decreased with increasing soil depth except T and TS. The content of MBC decreased from sowing to harvest.3. The number of soil bacteria and fungi decreased with increasing soil depth in 0-30 cm soil layer. The soil microbial population in 0-30 cm soil layer found in conservation tillage treatments was greater compare with T; NTS and TS treatments significantly increase the average number of soil bacteria, fungi and actinomycetes in 0-30 cm soil layer compare with T. Average number of bacteria, fungi and actinomycetes under NTS and TS were significantly greater compared with T by 46.51%, 76.01% and 82.16% in NTS and 19.01%, 57.36% and 50.69% in TS at sowing of spring wheat. Total number of bacteria, fungi and actinomycetes were significantly increased by 61.54%, 22.98% and 59.57% in NTS and 52.29%, 16.26% and 28.11% in TS compared with T at harvest of spring wheat.4. Compared with T, straw amendment(NTS and TS) significantly increased the upper layer(0-10cm) soil alkaline phosphatase activity(ALP). The ALP under NTS and TS was significantly higher than T in 0-5cm and 5-10 cm soil layer. The average ALP in 0-30 cm under NTS was increased by 55.62% at sowing and 5.87% at harvest of spring wheat compared with T. The ALP increase in different tillage practices from sowing to harvest.5. Significant positive correlation was observed between the average soil organic matter content and microbial biomass carbon content. The alkaline phosphatase activity, average number of bacteria in 0-30 cm soil layer and number of fungi and actinomycetes had a significant positive correlation with soil organic matter content. In the wheat plots, the correlation coefficient was higher between the number of bacteria and soil organic matter content, and higher in microbial biomass carbon in Pea-plots.The results of this study showed that conservation tillage improved SOM content in 0-30 cm soil layer, microbial biomass carbon content, number of microorganisms and alkaline phosphatase activity; all had significant positive correlation. Therefore, viewing these results from the soil biological point, conservation tillage improved the SOM content in 0-30 cm depth because it enhanced the microbial biomass carbon content, the alkaline phosphatase activity and number of microbes.