Effects of intercropping patterns on rhizosphere soil nutrients and microecological environment of walnut in karst area

Abstract

To study the effects of intercropping walnut in karst area on rhizosphere soil nutrients and microecological environment, four different planting modes of walnut in the northwest Guangxi karst area were selected as experimental subjects. The modes included intercropping walnut with mulberry (H-SS), walnut with Mahonia fortunei (H-SD), walnut with corn (H-YM), and monoculture walnuts (H-D). The physicochemical properties and microbial characteristics of the walnut rhizosphere and non-rhizosphere soils under different planting modes were analyzed using laboratory chemical experiments and Illumina Miseq PE300 high-throughput sequencing technology. The results were as follows: (1) The walnut rhizosphere soils of different modes exhibited different degrees of enrichment in total nitrogen (TN), total phosphorus (TP), total potassium (TK), available phosphorus (AP), soil organic carbon (SOC), and exchangeable calcium, while available nitrogen (AN) showed a deficiency. Among them, H-SS showed significant enrichment effects on TN, TP, and SOC, while H-YM demonstrated the best enrichment effects on AP, AK, and exchangeable calcium. (2) Sucrase activity, microbial biomass carbon and nitrogen, and bacteria all exhibited significant rhizosphere effects, with H-YM showing the highest sucrase activity, phosphatase activity, and microbial biomass carbon. However, intercropping modes reduced the rhizosphere effects of microbial biomass nitrogen and bacteria. (3) Under the three intercropping modes, the Shannon index of rhizosphere soil bacteria was higher than that of monoculture walnuts. (4) Intercropping could enhance the diversity of rhizosphere soil bacteria. Moreover, the diversity of rhizosphere soil microorganisms was mainly influenced by nutrients, while non-rhizosphere soil was primarily affected by enzyme activities. In conclusion, intercropping can increase the enrichment ratio of rhizosphere nutrients, enhance soil enzyme activities, and promote microbial proliferation. Among the four different planting modes, H-SS shows significant enrichment effects on TN, TP, and SOC in rhizosphere soil, and it also has the highest soil bacterial content. H-YM exhibits better enrichment effects on AP, AK, and exchangeable calcium in rhizosphere soil. Therefore, in practical production, intercropping with mulberry or corn can be chosen based on local farming practices to optimize land use and improve ecological benefits. This study is of great significance for the development of sustainable agriculture in the northwest Guangxi karst area and provides a scientific basis for agricultural production and ecological conservation in similar ecological environments. Additionally, this research offers new ideas and methods for promoting agricultural modernization and facilitating the rational utilization of land resources and improvements in the ecological environment in karst area.

Keywords

• karst area
• walnut
• intercropping
• soil nutrients
• microbial characteristics
• rhizosphere effect