Responses Of Soil Particulate Organic Carbon And Its Activity To Different Tillage Practices

In order to expand understanding of POC and tillage measures interaction, samples ofsoil were taken from9-year experimental fields in Guanzhong Plain to study the impact ofstraw returning or not on the content of POC and MOC in different soil layers in these fieldswhich were treated by four different tillage measures (Sub-soiling, rotary tillage, no-tillageseeding and conventional tillage). Results showed that:1. Effects of different tillage measures on POC and MOCThe content of POC decreased while MOC increased gradually with the increasing depthof the soil layers. In0-10cm layer of soil treated with straw returning，content of POC was5.36g/kg while no straw returning was5.03g/kg in Sub-soiling field. whether returning strawor not, the content of POC reached the highest level in all the tillage measures；Rotary tillagewas good for the accumulation of MOC in0-10cm and10-20cm; according to differentfrequencies, Sub-soiling could be divided into3different pattens(Sub-soiling every year、every two years and every three years),the increase of POC was the largest underevery-three-years Sub-soiling.2. Effects of different tillage measures on PON，POC/PON，TNThe content of PON，POC/PON，TN decreased gradually with the increasing depth of thesoil; in the four different layers, the difference of content of TN was not significant. In strawreturning fields, the increase of PON under sub-soiling was the largest comparing with controlgroup; whether returning straw or not, POC/PON reached the highest in sub-soiling fields.MOC/MON and TC/TN did not change much with the increasing depth of soil.3. Effects of different tillage measures on activity of POCThe content of easy oxidized particulate organic carbon, high active particulate organiccarbon、medium active particulate organic carbon and NaOH-extractible particulate organiccarbon decreased gradually, and change in0-20cm layer was the greatest.In no straw returning group in0-10cm soil layer under Sub-soiling, both the relativecontent of easy oxidized particulate organic carbon and the ratio of easy oxidized particulateorganic carbon to hard oxidized particulate organic carbon reached a maximum. Rate ofincrease of high active particulate organic carbon under rotary tillage was the largest, both the content and relative content of medium active particulate organic carbon were the most insub-soiling, while the content and relative content of NaOH-extractible particulate organiccarbon most in rotary tillage.In the straw returning group, both the content of easy oxidized particulate organic carbonand the proportion of easy oxidized particulate organic carbon to POC reached the highestlevel, while high active particulate organic carbon in sub-soiling，medium active particulateorganic carbon in rotary tillage, the content and relative content of NaOH-extractibleparticulate organic carbon were the most in sub-soiling in all the messures.From the average content of each indicators, whether returning straw or not, all thecontents of easy oxidized particulate organic carbon，high active particulate organic carbon，and NaOH-extractible particulate organic carbon were the most in Sub-soiling soil, thecontent of medium active particulate organic carbon reached the most in Rotary tillage whenreturning straw.4. Relativity among indexesThe indexes became less relevant with the growing depth of soil layer. in0-10，10-20，20-30cm soil layers, POC，TC and TN were significant at the0.05level and at the0.01level.In30-40cm soil layer, there had no significant correlation between POC and other indexes.In all the four soil layers, MOC had significant difference with TC and TN at the0.05or the0.01level, furthermore, with the depth of soil growing, the significant difference changedfrom0.05level to0.01level. In all the soil layers,easy oxidized particulate organic carbonpositively correlated with POC and TC; high active particulate organic carbon and mediumactive particulate organic carbon had significant relationship with TC， TN andNaOH-extractible particulate organic carbon only in the0-10cm soil layer, but not significantwhen the depth of soil increased. PON，TN，MON and medium active particulate organiccarbon mainly correlated significantly in0-10cm layer, but below0-10cm layer only PONand medium active particulate organic carbon significantly correlated.