Effects Of Multiple Cropping Patterns And Nitrogenapplication On Changing Characteristics Of Soil Organic Carbon

The dynamic changes of particulate organic carbon, easily oxidized organic carbon, soil humus carbon( humic acid carbon and fulvic acid carbon) were measured based on field experiments and laboratory analysis. The field experiment was implemented under different multiple cropping patterns taking three types of crops( soybean、potato、maize) as materials in three levels of farmland topsoils: 0~10cm, 10~20cm and 20~30cm respectively in semiarid and humid-prone regions of loess plateau. In order to provide the rationale for establishing an optimized multiple cropping patterns in arid crop area, the topsoil organic carbon fractions and their relationships, and their fertility effects and yield effects were measured, then the contribution of different level of nitrogen application to the transformation and accumulation under different multiple cropping patterns was measured, and correlations between organic carbon fractions and yield were analyzed. Meanwhile the dynamic changes of key factors affecting carbon metabolism including chlorophyll, saccharose, SS and SPS etc of different Plants,and the correlations between these factors and yield were analyzed. Influential mechanism about nitrogen application levels and different multiple cropping patterns to carbon metabolism were certain, these findings provided rationale for the balanced development of yield effect and ecological effect within agricultural ecological system. The main results were as follows:1. Effects of multiple cropping patterns and nitrogen application on soil particles organic carbon.The contents of particu1 ate organic carbon had an obvious fluctuation during the growth period of crops in winter rape crops and wheat crops rotation, and the POC showed different trends because of different crops. The accumulation of POC was 1.83~2.16g/kg, 1.31~2.80g/kg and 1.47~2.23g/kg in soybean, potato and maize farmland. The POC presented a trend of first decreasing and then increasing for soybean and potato farmland, and a change trend of “rise first and then decreased” for corn farmland, the total POC of three kinds of crop farmlands presented an increasing trend during the whole growth period of three crops. The winter rape crops rotation was conductive to the accumulation of POC in soybean and potato farmlands. And winter rape crops rotation helped the accumulation of POC in maize farmland. The POC contents in soybean and potato farmlands under the winter wheat crops rotation were higher 0.02~0.29g/kg and 0.13~0.69g/kg than that under the winter rape crops rotation respectively. However, the POC contents in maize farmlands under winter rape crops rotation was higher 0.01~0.23g/kg than that under the winter wheat crops rotation.Under the winter rape crops rotation, the difference of POC content were not significant(P >0.05) among different nitrogen applications treatments on soybean farmland; on potato farmland, there was significant different in POC content under N0 treatment and N240 treatment on the 60 th day after sowing, with others treatments it was not significant. on maize farmland, the difference of POC content were significant with N120 treatment, N0 treatment and N240 treatment on the 60 th day and 100 th day after sowing(P<0.05)。Under the winter wheat crops rotation, the contents of POC content in soybean farmland with N240 treatment were higher than those with N0 or N120 treatment on the 20 th day or 80 th day after sowing. In Potato farmland, POC of N120 treatment on the 80 th day was lower remarkably than that with N0 treatment and N240 treatment, the difference was not significant for other reproductive phase. In maize farmland the difference of treatments was not significant. Multiple cropping soybean, corn potato is conducive to the accumulation of soil POC. Accumulation of N120 treatment of soybean, potato soil POC under N240 treatment was higher than that of N0, N120; higher accumulation of N240 in soil of Maize under POC treatment. For both Winter rape and winter wheat crops rotation, the POC content and rates of POC/ TOC of different crop farmlands including soybean, Potato and maize decreased in an order, the content of POC and rate of POC/TOC in 0~10cm soil layer were highest then 10~20cm, that in 20~30cm was lowest.2. Effects of multiple cropping patterns and nitrogen application on soil easily oxidized organic carbonThe soil easily oxidized organic carbon contents had different dynamic changes in different crop farmlands. The accumulations of EOOC in soybean, potato and maize farmlands were 0.45~1.06g/kg,0.41~0.98g/kg and 0.44~1.07g/kg respectively. In soybean farmland the EOOC content presented a trend of first increasing then decreasing and last increasing. For both potato and maize farmlands, the change was shown the EOOC content continued to decrease from 20 th day after sowing to 100 th days(maturity). The changes of EOOC contents in soybean, potato and maize farmlands were 43.21~54.50%, 34.87~44.70% and 41.50~57.55% respectively。Under the winter wheat crops rotation, the content of EOOC content in soybean farmland with N240 treatment on the 40 th day after sowing were higher than that with N0 or N120 treatment. And the same variation took place for Potato and maize farmland. Under the winter wheat crops rotation, the difference of EOOC content in soybean farmland were significant with N0 treatment on the 20 th day than N120 and N240 treatment. The difference of other treatments was not significant. on Potato and maize farmlands the EOOC content changed little. Multiple cropping soybean than potato, corn is conducive to the accumulation of soil EOOC. Accumulation of N120 treatment of soybean, potato soil EOOC under N240 treatment was higher than that of N0, N120; higher accumulation of N240 in soil of Maize under EOOC treatment. For both Winter rape and winter wheat crops rotation, the EOOC contents and rate of EOOC /TOC in different treatments of different crop farmlands including soybean, Potato and maize had same change trends, the content of POC and rate of POC/TOC in 0~10cm soil layer were highest then 10~20cm, and in 20~30cm soil layer were lowest.3. Effects of multiple cropping patterns and nitrogen application on soil humus carbonThe contents of soil humus carbon in soybean, potato and maize farmlands presented a trend of first increasing then decreasing and last increasing on two fore-rotating crops farmlands and in three nitrogen application treatments. The soil humus carbon contents were 2.50~4.13g/kg, 1.60~3.85g/kg and 2.25~3.82g/kg, the humic acid carbon were 0.80~1.18g/kg, 0.66~1.57g/kg and 0.73~1.32g/kg, ant the fulvic acid carbon contents were 1.55~2.91g/kg, 0.82~2.35g/kg and 1.45~3.06g/kg for soybean, potato and maize farmlands respectively. On two fore-rotating crops farmlands, the difference of soil humus carbon content in soybean farmland were significant among N0, N120 and N240 treatments on the 80 th day and 100 th day after sowing and other reproductive phase. There was significant difference in soil humus carbon content between the growth periods(on the 80 th day and 100 th day after sowing) and other growth periods on soybean farmland in N0, N120 and N240 treatments, on two fore-rotating crops farmlands. However the difference of soil humus carbon content in potato farmland were significant only under N0 treatment on the 20 th day and 100 th day after sowing and that was non significant during other growth periods. On rape crops farmland, the difference of soil humus carbon content was significant between the growth period(the 100 th day after sowing) and other periods in N0 treatment and N240 treatment(P<0.05).The contents of soil humus carbon, humic acid carbon and fulvic acid carbon in cropping soybean field were higher 0.26~0.48g/kg,-0.07~-0.34g/kg and 0.35~0.62g/kg than those of cropping potato field, and 0.08~0.54g/kg, 0.11~0.33g/kg and 0.15~0.42g/kg than those of cropping maize field。It could be concluded that cropping soybean was conductive to soil humus carbon accumulation. soil humus carbon contents in 10~20cm soil layer on soybean and potato farmlands were higher than those in 0~10cm and 20~30cm soil layer in every nitrogen applications. Accumulation of soil humus carbon in N240 treatment was higher than that in N0 treatment and N120 treatment, and the accumulation was decreasing with the soil layer depth.4. Effects of multiple cropping patterns and nitrogen application on carbon metabolism of plantsThe changes of changes of Chlorophyll a, Chlorophyll b and Chlorophyll a+b of leaves in soybean and potato farmlands were identical and had unimodal curve on two fore-rotating crops farmlands(winter rape and winter wheat), and the amount of them was higher on the 20 th day after sowing than on the 100 th day’. However the dynamic change of carotenoids was irregular and need to be studied further.The contents of Chlorophyll a, Chlorophyll b and Chlorophyll a+b of soybean leaf in soybean in winter wheat farmland were higher 0.01~0.19mg/g, 0.01~0.06mg/g and 0.01~0.25mg/g than in winter rape farmland. And the contents of Chlorophyll a and Chlorophyll a+b of maize leaf in soybean in winter wheat farmland were higher 0.09~0.11mg/g and 0.04~0.14mg/g than in winter rape farmland. So we concluded that winter wheat farmland was conductive to accumulation of Chlorophyll accumulation. During the whole growth period of soybean, potato and maize, leaves had bimodal curves in contents of Sucrose, Sucrose synthase(SS) and Sucrose–phosphate synthase(SPS) with the growth. The demand of nitrogen during the whole growth period of maize was higher than that of potato and soybean. And the sucrose content in N240 treatment was higher N0 and N120 treatments, the difference among the treatments was not significant. Change of SS under Winter wheat crops rotation was higher than that of Winter rape crops rotation for soybean, potato and maize. The activities of Sucrose–phosphate synthase of soybean and potato under Winter rape crops rotation was higher 0.18~2.05(mg Sucrose/g FW/min) and 1.57~3.81(mg Sucrose/g FW/min) than those on fore-rotating crops of wheat.5. Correlations between yield and factors of the composition of organic carbon and carbon metabolismThe differences of contents of organic carbons including TOC, POC, EOOC, Humus carbon etc with treatments of N0, N120, N240 treatments under on two fore-rotating crops were not significant. There was a strong negative correlation between EOOC and POC in potato farmland with N240 treatment(P<0.01), on fore-rotating crops farmlands of rape. And the difference in other treatments was not significant. there was remarkable positive correlation between POC and TOC(P<0.05)in maize farmland with N120, and negative correlation for Humus carbon and TOC with N240 treatment(P<0.05).and the Humus carbon was negatively correlated with EOOC(P<0.05)under winter wheat crops rotation with N120 treatment, it was not significant in other treatments. under winter rape crops rotation, there were strong positive correlations among chlorophyll a and chlorophyl b, carotenoids, chlorophyll a+b, sucrose for soybean, potato and maize crops(P<0.01). and the same correlations for sucrose and SS(P<0.01), also for SS and SPS(P<0.01). under winter wheat crops rotation, the chlorophyll a was very, significantly and positively correlated with the chlorophyl b, chlorophyll a+b and SS for soybean, potato and maize crops(P<0.01). The sucrose was significantly and positive correlated with and SS(P<0.05), the same for SS and SPS(P<0.05).