[Soil nitrogen content and enzyme activities in rhizosphere and non-rhizosphere of summer maize under different nitrogen application rates.] / æ–½æ°®é‡å¯¹å¤çŽ‰ç±³æ ¹é™ å’Œéžæ ¹é™ åœŸå£¤é ¶æ´»æ€§åŠæ°®å«é‡çš„å½±å“.

A field experiment was conducted on fluvo-aquic soil in the North China Plain to study the effects of nitrogen application rate on soil nitrogen contents and enzyme activities in rhizosphere and non-rhizosphere of summer maize. The results showed that the soil enzyme activities under different nitrogen application rates showed similar seasonal patterns. In comparison to no nitrogen ferti-lizer treatment, all nitrogen application treatments significantly increased NO3--N contents in rhizosphere and non-rhizosphere soils, NH4+-N content in rhizosphere soil and the activities of ß-N-acetylglucosaminidase, ß-glucosidase, ß-xylosidase and Cellobiohyrolase. During the whole summer maize growing season, the NO3--N content in non-rhizosphere soil was significantly higher than that in rhizosphere soil. The NH4+-N content in non-rhizosphere soil was also significantly higher than that in rhizosphere soil at filling stage but significantly lower at seedling and maturity stages. Furthermore, soil enzyme activities in rhizosphere soil were significantly higher than those in non-rhizosphere soil. Effect of nitrogen application on soil organic carbon content was not significant. Soil total nitrogen content increased significantly when the nitrogen application rate was 0-180 kg·hm-2 but decreased significantly when the rate was higher than 180 kg·hm-2. Generally, a proper rate of nitrogen fertilizer application could significantly increase soil enzyme activities and total nitrogen content, and then improve soil biochemistry properties.

[Effects of long-term tillage measurements on soil aggregate characteristic and microbial diversity].

Soil aggregate stability and microbial diversity play important roles in nutrient recycling in soil-crop systems. This study investigated the impacts of different soil tillage systems on soil aggregation and soil microbial diversity based on a 15-year long-term experiment on loess soil in Henan Province of China. Treatments included reduced tillage (RT), no-tillage (NT), sub-soiling with mulch (SM), wheat-peanut two crops (TC), and conventional tillage (CT). Soil aggregates were separated by wet sieving method, and soil microbial (bacterial, archaeal and fungal) diversity was examined by using the techniques of denaturing gradient gel electrophoresis (PCR-DGGE) analysis. The results showed that water-stable macroaggregates concent (R0.25) and the mean mass diameter (MWD) in the surface soil significantly increased under NT, SM and TC, R0.25 increased by 21.5%, 29.5% and 69.2%, and MWD increased by 18.0%, 12.2% and 50.4%, respectively, as compared with CT. Tillage practices caused changes in bacterial, archaeal and fungal community compositions. With NT, SM and TC, the bacterial, archaeal and fungal Shannon indices increased by 0.3%, 0.3%, and 0.6%, and 20.2%, 40.5%, and 49.1%, and 23.7%, 19.5%, and 25.8%, respectively, as compared with CT. Both bacterial and archaeal Shannon indices were significantly correlated with the indices of R0.25 and MWD, while the fungal Shannon index was not significantly correlated with these two indices. In conclusion, conservation tillage, including NT and SM, and crop rotation, including TC, improved soil aggregation and soil microbial diversity.

[Effects of tillage pattern on the flag leaf senescence and grain yield of winter wheat under dry farming].

A field experiment was conducted to study the effects of different tillage patterns, i.e., deep plowing once, no-tillage, subsoiling, and conventional tillage, on the flag leaf senescence and grain yield of winter wheat, as well as the soil moisture and nutrient status under dry farming. No-tillage and subsoiling increased the SOD and POD activities and the chlorophyll and soluble protein contents, decreased the MDA and O2(-.) contents, and postponed the senescence of flag leaf. Under non-tillage and subsoiling, the moisture content in 0-40 cm soil layer at anthesis and grain-filling stages was decreased by 4.13% and 6.23% and by 5.50% and 9.27%, respectively, and the contents of alkali-hydrolysable N, available P, and available K in this soil layer also increased significantly, compared with those under conventional tillage. Deep plowing once decreased the moisture content and increased the nutrients contents in 0-40 cm soil layer, but the decrement and increment were not significant. The post-anthesis biomass, post-anthesis dry matter translocation rate, and grain yield under no-tillage and subsoiling were 4.34% and 4.76%, 15.56% and 13.51%, and 10.22% and 9.26% higher than those under conventional tillage, respectively. It could be concluded that no-tillage and subsoiling provided better soil conditions for the post-anthesis growth of winter wheat, under which, the flag leaf senescence postponed, post-anthesis dry matter accumulation and translocation accelerated, and grain yield increased significantly, being the feasible tillage practices in dry farming winter wheat areas.

[Spatial autocorrelation analysis on soil organic carbon distribution in Henan Province].

With spatial autocorrelation analysis, this paper studied the temporal and spatial variations of soil organic carbon (SOC) storage in Henan Province during the period from the 1st national soil survey (1958) to the 2nd national soil survey (1985). The results showed that spatial auto-correlation indices could better describe the spatiotemporal variation of the SOC storage between the two soil surveys. The total SOC storage was 54.93 x 10(8) t in 1958 and 69.65 x 10(8) t in 1985, with an annual increase of 1%, and the SOC density had a trend of higher in southeast and west Henan, followed by north and central Henan, and east Henan. The SOC storage per unit area decreased more quickly in southeast Henan, with the maximum of 1.57% per year, while increased greater in east Henan, with an average rate of 5.27% per year. The spatiotemporal variation of SOC storage had a close correlation with the original SOC content, i. e., the higher the original SOC content, the more greatly the SOC storage decreased.