| Soil organic matter (SOM) is an important indicator of soil fertility, it is of great significance to study its temporal-spatial evolution in order to ensure stable or higher crop yields as well as improve soil fertility.Based on the data of five long-term experiment sites (Hengshui, Changping, Xinji, Zhengzhou and Quzhou) in the NCP, this thesis assesses the applicability of DNDC model and analyzes the impact of different fertilization regimes, tillage and straw management modes on crop yields and topsoil soil organic carbon (SOC). For the modes of combining fertilizers with manures or straw at each site, scenario analysis was conducted to optimize the combining ratios. Besides, we simulated the future trends of crop yields and SOC from present to 2099, based on the future climate datasets under the RCP4.5 and present climate scenario. Moreover, we conducted the regional calibration and validation by utilizing the data of 9 monitoring sites in the Beijing-Tianjin-Hebei Plain (BTH), and then simulated the temporal and spatial variation of SOC and crop yields during 1980-2014 at regional scale. The main results of our study were as follows:Performance of DNDC model in simulating crop yields and topsoil SOC were overally good except that it performed relatively poorly in simulating winter wheat yield of treatment A1B1 in Hengshui site with EF being-0.11 and summer maize yield of treatment M in Changping site with EF of-0.25. And the evaluation statistical indices for winter wheat yields of 5 experiment sites were: modeling efficiency (EF) ranging 0.07-0.94, normalized root mean square error (NRMSE) ranging 8.8%-66.4% and index of agreement (d) ranging 0.66-0.98; and the evaluation statistical indices for summer maize yields were EF ranging 0.24-0.96, NRMSE ranging 2.6%-40.1% and d ranging 0.56-0.99; three valuation statistics for SOC were EF within 0.09-0.98, NRMSE within 2.9%-24.2% and d within 0.45-0.98. The determination coefficients (R2) between simulated and measured values of the winter wheat yields, summer maize yields and SOC contents were 0.741-0.973,0.721-0.973 and 0.308-0.763 respectively (P<0.05) and reached a significant level.In Hengshui, the optimal ratio of maize straw surrogating fertilizer was 40% when the total fertilizer rate was 180 kg N ha-1; in Changping, the optimal ratio of chicken manure surrogating fertilizer was 30% with total fertilizer rate being 270 kg N ha-1; in Xinji, the optimal ratio of compost surrogating fertilizer was 40% with total fertilizer rate being 180 kg N ha-1; Zhengzhou, the optimal ratio of bean cake surrogating fertilizer was 10% with total fertilizer rate being 150 kg N ha-1; in Quzhou, under conventional tillage and no-tillage practice, the optimal ratios of wheat straw surrogating fertilizer were 40% and 10% with total fertilizer rate being 150 kg N ha-1. And the results of scenario analysis of changing manure(or straw) ratio with fixed fertilizer rates were as follows:the ratio between fertilizer and maize straw was 1:2 (120 kg N ha-1 with 23726 kg straw ha-1) in Hengshui; the ratio between fertilizer and chicken manure was 1:0.33 (150 kg N ha-1 with 4000 kg ha-1) in Changping; the ratio between fertilizer and compost was 1:1.33 (120 kg N ha-1 with 32000 kg ha-1) in Xinji; the ratio between fertilizer and bean cake was 1:1.67 (120 kg N ha-1 with 2587 kg ha-1) in Zhengzhou; the ratio between fertilizer and wheat straw was 1:0.4(120 kg N ha-1 with 8727 kg ha-1) in Quzhou.Except treatment CK, future crop yields (2011-2099) of other fertilization regimes in Hengshui under RCP4.5 scenario was 1.2%-3.3% higher than those under present scenario. In Changping, future crop yields (2000-2099) under RCP4.5 scenario was 0.7%-15.6% higher than those under present scenario. The increasing rate under scenario 4.5 in Xinji was 0.4%-10.5%; and in Zhengzhou, the crop yields under scenario RCP4.5 were 4.2%-6.0% higher than those under present scenario; while in Quzhou, future crop yields of treatments CK and F under scenario RCP4.5 decreased compared with those under present Scenario, yet those of treatments M and FM increased by 3.7% and 3.9% respectively. In terms of the future trend of SOC, for treatment CK without fertilization, SOC contents in Hengshui and Changping showed a decreasing trend under both RCP4.5 and present scenarios while SOC contents in Zhengzhou and Quzhou showed an increasing trend under both scenarios, moreover, SOC content in Xinji showed a rising trend under RCP4.5 yet a declining trend under present scenario. And both under RCP4.5 and present scenarios, the highest annual increasing rate of SOC contents occurred in treatments combining fertilizers with manure (or straw), i.e., treatment FM, exceptionally in Quzhou the highest increasing rate occurred in treatment F which was due to the no-tillage practice. In addition, in the 5 experiment sites, the increasing rate of SOC contents under RCP4.5 were higher than that under present scenario.During 35 years(1980-2014), overally SOC content in the BTH plain was higher in the north part and lower in the southern part. And SOC content in the middle of Hebei province (e.g. Bazhou city) showed a gradual decreasing trend which became more evident after 2000, in addition, the area with higher SOC content in this region decreased. However, the SOC content of Wuqing in Tianjin gradually increased and the area with higher SOC content also expanded. Without straw retention, area with declining SOC content accounted for 10.7% of the BTH plain, which is located in the middle of Hebei. Besides, area with SOC increase of 0.4-0.8 g kg-1 accounted the largest area (60.3%) including the central, south-central and eastern part of Hebei province, Tianjin and eastern part of Beijing. The highest SOC increase (1.5-2 g kg-1) occurred in the southernmost part of Hebei which only accounting for 3.5% of the total area. However, under straw retention since 1999, the greatest SOC increase during 35 years was 5-8 g kg-1 and the least increase was 1.5-2 g kg-1, which was higher than that without straw retention, indicating that straw retention can significantly increase SOC content. During 1980-2014, crop yields in the BHT plain presented a trend of higher in the northeastern part and lower in the southwestern part, and the area with higher crop yields was basically consistent with area with relatively higher SOC content. |
PDF Full Text Request