Effects Of Different Conservation Tillage Measures On Soil Organic Carbon Pool And Soil Nutrient In Condition Of P-W Rotation

Long—term field experiments on the responses of soil organic carbon(SOC) andactive organic carbon(AOC) to different tillage patterns in rainfed farming systemswere conducted in Ding Xi on the western Loess Plateau．The experiment wasfully-phased with two rotation sequences．Phase1started with field pea (Pisumsativum) followed by spring wheat (Triticum aestivum)(P→W)whereas phase2started with spring wheat followed by field pea(W→P). The effects of conventionaltillage and three conservation agriculture patterns[conventional tillage(T)，conventional tillage with stubble incorporation(TS)，no till with no stubble(NT)，notill with stubble retention(NTS)]were studied. Readily oxidizable carbon (ROC)、microbial biomass carbon(MBC) and water-soluble organic carbon(WSOC) wereconsidered as indicators of AOC with total nitrogen and available nitrogen，and weremeasured together with SOC contents in soil layers of0-5cm、5-10cm、10-30cm、30-50cm and50-80cm.Total phosphorus、total potassium、available P and available Kcontents were studied at0-30cm soil layer. Main results are as follows:(1)In comparison with T,3conservation tillages can be increased SOC、ROC、MBC and WSOC contents, the treatment of no till with stubble retention wereespecially the best. This conclusion illustrated that conservation tillages such asrotation、no-tillage and stubble incorporation benefited the carbon sink of farmlandand it was the key approaches to sustainable agriculture and environment. The SOCand AOC contents were decreased with the increase of soil depth and between theconservation tillages, NTS decreased in large amplitude. Correlation analysis showedthat, the AOC indicators had a significant positive relationship(p＜0.05) with the soilorganic carbon. It can be summarized that different tillage treatments had the sameeffect on the tendency of change of the content of SOC and AOC indicators.(2)Compared to the T treatment,3conservation tillages treatments cansignificantly add the SOC and total N contents in surface layer (0-30cm) but reduce inthe deep layer (30-80cm). Conservation tillages treatments added SOC and total Ncontents in the whole profile (0-80cm), but not significantly. It can be learned that3 conservation tillages were beneficial to accumulate the contents of SOC and total N insurface layer but were not in the deep layer. Available N and total N contents in soilprofile were decreased with the increase of soil depth.(3)In comparison with T, NTS and TS treatments increased the stock of SOC andtotal N, while NTS and NT treatments decreased the stock of them. Compared to theT, no tillage and stubble incorporation enhanced the SOC and total N stocks in thesurface layer. It means that no tillage and stubble incorporation treatments werebeneficial to accumulate the stocks of SOC and total N in the surface layer, but the notillage had no benefits for the stocks of them in the deep layer. No tillage treatmenthad slightly reduced the stocks of them in whole profile. The numerical value of soilC/N in differently layers ranged10.04from11.55. It was so relatively low thatenhanced the corrupt degree of organic matter.(4)The total P and available P contents in each treatment had the same tendencyof change and decreased with the increase of soil depth. The contents of total P andavailable P in the whole deep layer (0-30cm) were sorting for NTS＞TS＞NT＞T.Compared to the T,3conservation tillage treatments can obviously enrich thecontents of total P and available P in the surface layer. It produced stratification ofsoil nutrients. While the total K and available K contents in each treatment had thesame tendency of change and added with the increase of soil depth. The contents oftotal K and available K in the whole deep layer (0-30cm) were sorting for NTS＞TS＞NT＞T.(5) In two sequence rotation systems, the contents of total N、total P、available Nand available P had a significant positive relationship with the soil organic carbon,while the contents of total K and available K had a significant negative relationshipwith the soil organic carbon.