不同措施对滨海盐渍土壤呼吸、电导率和有机碳的影响

在苏北滩涂围垦区的轻度和中度盐渍土上,通过田间试验,研究了不同农田管理措施(传统耕作、施用有机肥、氮肥增施、秸秆还田和免耕)对土壤盐分、呼吸和有机碳等的影响。结果表明,0~40cm土层平均电导率在玉米种植季明显升高,小麦种植季出现小幅降低,轻度盐渍土的电导率为4.57~8.20 d S m~(~(-1)) ,中度盐渍土为4.89~10.13 d S m~(~(-1)) ,处理之间秸秆还田最低,免耕最高,秸秆还田和施用有机肥有效减少了土壤盐分含量。与中度盐渍土相比,轻度盐渍土的呼吸强度较高,在夏玉米和冬小麦种植季节分别高约16%和18%。有机肥、氮肥增施、秸秆还田处理的土壤呼吸均高于对照,而免耕较低。两组试验的土壤有机碳和微生物生物量碳均有缓慢增加,其中施用有机肥和秸秆还田可以大幅提高其含量。轻度盐渍土壤代谢熵高于中度盐渍土,总体上对照最高,免耕最低。

Effects of Farming Practice on Soil Respiration, ECe and Organic Carbon in Coastal Saline Soil

In China, the pressure of the shortage of land resources is getting more and more intense gradually, so it is very important to develop sustainable utilization and optimal management of the coastal saline soil resources. On the other hand, climate change is intensifying salinization of the inshore saline soil, thus causing a series of ecological environment problems. However, soil, as an important component of the global carbon pool, plays an important role in regulating the carbon cycle. A field experiment was carried out to study effects of various farming practices on electrical conductivity (ECe), total respiration, organic carbon (OC), microbial biomass C (MBC), and metabolic quotient (qCO2) in coastal saline soil. In the experiments, maize was cultivated in rotation with wheat in two tracts of saline soil different in salinity, Soil A (slightly salinized soil) and Soil B (moderately salinized soil), and both tracts were subjected to five different treatments or farming practices, that is (1) CK, conventional farming; (2) OF, application of organic fertilizer at a rate of 1.5 T hm-2; (3) NF, application of a higher rate of nitrogen fertilizer, about 150% of that in CK; (4) S, incorporation of straw at a rate of 5 T hm-2; and (5) NT, no tillage. It was found that after two crops were harvested, ECe varied in the range from 4.57 to 8.20 dS m-1 in Soil A, and from 4.89 to 10.13 dS m-1 in Soil B, and was the lowest in Treatment S and the highest in Treatment NT, which indicates that in corporation of straw and application of organic fertilizer effectively reduced salt content in the surface soil. Compared to Soil B, Soil A was higher in mean soil respiration intensity, 16% higher during the summer maize season and 18% higher during the wheat season. Treatments OF, NF and S were all higher than CK in soil respiration in comparison with CK, and only Treatment NT was a bit lower. In terms of soil respiration intensity measured in the end of the experiment, the treatments followed an order of S > OF > NF > CK > NT, regardless of soil salinity. When soil ECe got higher than the critical value, soil respiration rate began to slow down. After the corps were harvested, SOC and MBC tended to increase, especially in Treatment OF and S. The treatments varied sharply in SOC and MBC content, Which were significantly and positively related to soil respiration. That is to say, with increase SOC content, content of the matrix which soil microbes can decompose into organic carbon increased, thus releasing more CO2. However, organic carbon did not have any linear relationship with ECe. Soil A was slightly higher than Soil B in qCO2 and among the treatments, CK was the highest and NT was the lowest. Comparison of the two groups of treatments in the experiment indicates that the soil electrical conductivity and organic carbon content were the two main factors affecting CO2 release. All in all, though Treatment NT lowers soil respiration intensity and, increases organic carbon and microbial biomass carbon contents, it increases soil salinity too. This study holds that incorporation of straw and application of organic fertilizer are two optimal farming practices that can be adopted to ameliorate coastal tidal flats, improve soil fertility, promote crop growth, alleviate soil salinity and increase crop yield. Therefore, the practices of organic fertilizer application and straw incorporation have a great potential for extension in coastal polders.