Trend Of Soil Organic Matter And Influencing Factors In Different Cropping Systems In Huanghuaihai Plain

Soil organic matter plays a crucial role in soil fertility, environmental protection and sustainable development of agriculture. Establishing inventory of soil organic carbon is thus necessary for the development of strategic policies regarding the global agricultural production and environmental changes. Carbon sequestration is very important not only to improve soil quality and increase economic crop production, but also to increase soil carbon storage for carbon trading and mitigating CO2 emissions from soil profile. Thus, increasing soil organic matter content is of importance to the sustainable development in China and the whole world. Therefore, by using statistical data, literatures and the principle of soil organic matter balance, this paper preliminarily investigated the manure application rates and utilization status, trend of soil organic matter and the relationship between the manure application rates and the magnitude of soil organic matter change in Huanghuaihai Plain.1. Analysis on long-term trials of 5 to 15 years in the Huanghuaihai plain showed that: the change of SOM was positively correlated to the amount of straw stubble amendment and negatively correlated to N application rate. Further analysis was performed after dividing the data into two classes which the N rate was either > 330 kg/hm2 (HNPK) or < 330 kg/hm2 (NPK), results indicated that positive linear relationship between the change of SOM and the amount of straw bubble return at extremely significant level was obtained, which demonstrated a relatively large impact on soil organic matter. Model results showed that, the loss of SOC was much stronger at HNPK level than NPK level and an amount of straw-stubble amendment of 7254 kg/hm2 was required to maintain soil organic carbon (MSC) at HNPK level and 1297 kg/hm2 at NPK level respectively.2. During 1980 to 2005, the average production and return of straw stubble and root were increased in HuangHuaiHai region, while these values decreased since 1995 in Beijng. In addition, the average content of soil organic matter in this region increased, which indicated a steadily low increase before 1995 and then a relatively large variation afterwards. It should be noted that there was a declining trend in soil organic matter content in Bejing area. There was no significant relation between soil organic matter and the amount of straw stubble return. While during in 1980s which was associated with relatively low fertilization rate, extremely significant relationship between the organic matter change and the straw stubble return was observed; however, such relationship was only found in Tianjin, Shandong and Henan. It was concluded that high fertilization rate was taken from early 1990s, where Shandong was the earliest and Henan was the latest province. It was also indicated that the impacts of root exudates must be taken into account when evaluating the change of soil organic carbon because it was a non-negligible part of carbon input.3. The total production of human and livestock manure in Huanghuaihai plain was increased during 1980 to 2005, where human was the major contributor (about 50%) in Beijing and Tianjin and the livestock (about 80%) in Henan and Hebei provinces. During 2000 to 2005, the soil organic matter in vegetable soils decreased in Beijing and Tianjin but increased in Hebei and Henan provinces, significant positive relation between SOM and the straw stubble return was found in Tianjin, Beijng and Hebei, and the respective MSC for these three regions were 3737.4 kg/hm2,2937.6 kg/hm2 and 4765.4 kg/hm2.4. From 2000 to 2005, in orchard system, the lowest amount of fecaluria application per unit area was in Tianjin, and the greatest was in Hebei which was about 3.3 times of Tianjin. The return of fecaluria was increased in Beijing, Tianjin and Hebei except in Henan province. In addition, the soil organic matter in Beijing, Hebei and Henan was slightly increased but decreased in Tianjin. Significant relationship between fecaluria return and soil organic matter was only found in Hebei and Tianjin but no such relationship was found in Beijing and Henan.5. The SOM contents of these three planting systems were in an order of vegetable fields>wheat-corn rotation system>orchard. From 1980 to 2005, the SOM of wheat-corn rotation system was associated with a slow but steady increase; the orchard system was with higher increase rate of soil organic matter than vegetable lands during 1999-2005; for vegetable lands, two out of four regions were with a decrease of soil organic matter; while for orchard system, the declining trend was only found in Tianjin where the declining rate was less than vegetable land.