| Continuous monoculture can negatively affect crop yields and soil quality, which is an important issue in agriculture. In order to solve the broccoli and cucumber continuous cropping obstacle, this paper puts forward two kinds of different cultivation measures. Soil biological activity, the quality and production of vegetable were analyzed. The specific objective is to explore efficient and environmentally friendly technologies that can alleviate continuous cropping obstacles and improve the microenvironment of cropland soil.1. Remission effects of broccoli continuous obstacle in intercropping waxy maize and maize straw returningThree treatments were assessed: relay intercropping of broccoli and waxy maize(B/M-B); relay intercropping of broccoli and waxy maize with residues retention(B/MR-B);and broccoli monoculture(B-B).1.1 Intercropping waxy maize and maize straw returning contribute the functional diversity of the soil microbial communityThe "average well color development"(AWCD) curve values followed the order B/MR-B > B/M-B > B-B. The diversity of the microbial community, including Shannon index, Simpson index, and Mc Intosh index was also higher under the B/MR-B treatment than that under monoculture. A principal component analysis(PCA) showed that the microbial communities from B/MR-B soils differed from those of control soils. The carbon(C) source utilization by the soil microbial community differed between intercropping and monoculture,and the main C sources were carbohydrates, carboxylic acid, amino acids and polymers.Furthermore, the communities from B/MR-B mainly revealed a preference for amino acids and polymers. That suggests the microbes degrading amino acids and polymers were mainly affected by broccoli continuous cropping in bulk soil. The available nitrogen(N), potassium(K) and phosphorus(P) had an obvious impact on the functional diversity of the soil microbial community. In addition, the C-source utilization by microorganisms were significantly impacted by p H and available K and P.1.2 Intercropping waxy maize and maize straw returning contribute the soil biological activity and the quality of vegetableSoil microbial biomass carbon(SMBC), soil microbial biomass nitrogen(SMBN)increased effectively under intercropping and straw returning. B/MR-B is beneficial to improving the activity of soil urease, sucrase and neutral phosphatase and promoting soil organic transformation and nutrient availability. The secretion of hydrogen peroxide by rootsduring the earlier stage of straw returning led to the increased activity of soil catalase.However, intercropping had improved the nutritional status of the rhizosphere and reduced the toxicity of the hydrogen peroxide. Soil enzyme activity changes were correlated with SMBC and SMBN. Soil urease activity, sucrase activity, neutral phosphatase activity and catalase activity had significantly positive correlations with SMBC. Soil urease activity,sucrase activity, neutral phosphatase activity had significantly positive correlations with SMBN. The nitrate of broccoli was moderate. Intercropping reduced nitrate content, straw retention significantly increased nitrate content, but the content was within the scope of security. Although the vitamin C, soluble suger and free amino acid of the spring broccoli were reduced, the intercropping and straw returning system could improve soil improvement which could lay a good foundation to improving the quality of the autumn broccoli. At the same time, intercropping and straw retention significantly increased the yield of broccoli.2. Remission effects of cucumber continuous obstacle in different application rates of calcium cyanamideCalcium cyanamide(Ca CN2) has efficient impacts not only on nutrition supplies but on suppressing soil pathogens. With soil of cucumber continuous cropping system, the effect of Ca CN2 co-applied with cucumber straw retention on soil microbial should be concerned. Four treatments were set in the pot experiment, as follows: CK(null Ca CN2), Ca CN2-90(1350 kg ha-1), Ca CN2-60(900 kg ha-1), Ca CN2-30(450 kg ha-1).The results indicate that, SMBC and SMBN were improved with the increase of Ca CN2.In the seeding stage, the treatments with Ca CN2-60 and Ca CN2-90 did not increase SMBC in0~10 cm soil layer. In the primary fruit stage, SMBN was significantly decreased with Ca CN2 application. Calcium cyanamide was favorable to decaying straw and releasing nutrients,contributing to increasing soil organic matter. Moreover, the higher Ca CN2 application rates could accelerate straw decomposition. Soil urease activity was significantly increased with Ca CN2-90. Calcium cyanamide effectively increased soil catalase activity and polyphenol oxidase activity. The appropriate application rate of Ca CN2 could improve catalase activity,while catalase activity and polyphenol oxidase activity decreased with excessive use of Ca CN2. Soil organic matter and soil enzyme activity changes were correlated with SMBC and SMBN. Soil organic matter, urease activity and catalase activity had significantly positive correlations with SMBC and SMBN. However, polyphenol oxidase activity was negatively correlated to SMBC and SMBN. The average single fruit weight of per plant, yield per plant and total outpu of cucumber were highest on the Ca CN2-60. However, the excessive use of Ca CN2 reduced the cucumber production. With the increase of Ca CN2, the nitrate ofcucumber increased gradually, and compared with CK, Ca CN2-30 treatment significantly reduce the nitrate content. While with the increase of Ca CN2, the vitamin c, free amino acid,soluble suger and soluble protein content would increase, then the four indicators above would decrease, the treatment Ca CN2-60 was the best. |
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