Improving biological traits by soda alkali-saline land diking for fish

Abstract: Soda saline-alkali land is one of the main types of salinized land resources in China. Due to the influence of semi-arid monsoon climate, groundwater condition and geochemical process of element migration in Tongliao City of Inner Mongolia, a large area of saline-alkali soil has been formed. The low-lying saline-alkali land in the West Liaohe River Basin belongs to the soda alkaline soil with high alkalinity. And for most of the barren bare alkaline soil, soil productivity was very low. Planting rice after embankment and fish culture in saline-alkali soil was one of the effective ways of improving saline-alkali soil. In order to investigate the improvement effect of embankment and fish culture on saline-alkali soil, the biological traits and respiration of various soil samples were tested in 2016. The pH value of soil samples was 9.52, and soil respiration was 1.10 mg/g. The activity of soil enzyme and the amount of soil microorganism were the important indices to indicate the soil fertility level. The biological traits included the numbers of microorganisms (nitrite bacteria, cellulose decomposing bacteria, phosphorus bacteria), which were counted with dilution flat plate coating method, and the soil enzyme activity included phosphatase, urease, cellulase, polyphenol oxidase, and catalase, which were determined by colorimetric method and titration method. Additionally, the soil respiration was measured by alkali absorption titration method. The soil samples were taken from the ponds in Horqin Left Middle Banner, Tongliao City, where fish culture lasted for 3, 5 and 8 years, respectively, and rice was planted after 5-year fish culture and bare alkaline soil was taken as the control. The results showed that among the fish culture of different years, planting rice after 5-year fish culture had the most obvious improvement effect on the microorganism. Compared with the bare saline soil, the numbers of soil bacteria, cellulose decomposing bacteria, rice nitrite bacteria, and phosphorus bacteria were increased respectively by 2.60×106, 0.66×104, 7.84×105, and 0.55×105 cfu/g. It was not that the longer the fish culture time, the better the improvement effect on the soda saline-alkali land. Except the activity of polyphenol oxidase that was the highest in the bare alkaline soil, all the other enzyme activities had the most obvious improvement in the soil of fish culture for 5 years. The activities of urease, phosphatase, catalase and cellulase were increased respectively by 0.008 mg/g every 24 h, 0.153 mg/g every 24 h, 2.035 mg/g every 20 min and 0.399 mg/g every 72 h. The release amount of CO2 was the highest in the soil of fish culture for 8 years, 7.41 mg/g higher than that in the bare alkaline soil. Only bacteria number was positively correlated with soil respiration (P<0.05). There was no correlation between soil biological properties and soil respiration. The research has a certain reference value to the regional follow-up use of the saline-alkali land. In the early stage of utilization, we should pay attention to the improvement of fertilizer, increase the application of organic manure, rationally arrange irrigation, and make the utilization of soda salinized soil develop in a benign direction. We will study the effect of different ages on the nitrogen, phosphorus and potassium of the soda saline-alkali soil after embankment and fish culture. It will provide a reliable basis for the protection and utilization of soda saline-alkali land resources.