Effects of vegetable planting ages on the physical and chemical and biological properties of greenhouse soils in Beijing

Objectives Vegetable planting ages have different impaction on the soil ecological environments, especially inside green houses. The properties of soil physical and chemical, the population of soil microbial and the soil nematode community structures in the soils under different vegetable plantation age were determined in this paper, aiming to provide reference for the scientific management of green house soil.

Methods The open field was taken as control (CK), and the nearby greenhouses with planting ages of 3 years, 5 years, 8 years and 12 years were chosen for the research in Yanqing, Beijing. The soil samples at depth of 0−30 cm were collected with four replicates. The physical and chemical properties were analyzed using conventional chemical methods. The population of bacteria and fungi and the composition of soil nematode communities were measured using fluorescence quantitative method and nematode morphological identification methods, respectively.

Results With the increase of vegetable plantation age, soil bulk density and pH value were decreased, while soil total porosity, EC, SO₄^2–, Ca²⁺ and organic carbon (SOC), NH₄⁺-N, NO₃^–-N content were increased continuously. The number of both the soil bacteria and fungi showed trend of increasing firstly and then decreasing, and all significantly higher than the CK (P < 0.05). The abundance of Meloidogyne, Helicotylenchus and Heterodera were increased steadily with the planting ages, and the density of soil nematode and the abundance of plant-parasites nematode were increased significantly (P < 0.05), while the abundance of bacterivores, fungivores, predators/omnivores were gradually decreased. The diversity index of H′, SR and stability index of J′ in nematode communities were increased firstly and then decreased, compared with CK, the indexes in planting ages 12 year were decreased significantly (P < 0.05). In all the tested fields, the NCR > 0.5, which indicated the soil food web was dominated by bacterial channels, and the decomposition of organic matter depended mainly on bacteria in the study. The WI and MI were decreased gradually, while the PPI showed the opposite trend, the WI < 1 in planting ages of 12 years, which showed that the soil mineralization pathway changed into the main participant from plant to plant-parasites nematode, the soil ecosystem was disturbed gradually and the soil health was worse. The redundancy correlation analysis of soil environmental factors and the number of soil organisms showed that soil pH, soil bulk density, total porosity, EC, organic matter, SO₄^2–, NH₄⁺-N and NO₃^–-N were the key influencing factors on the number of bacteria, fungi and nematode. Therefore, the composition of soil organisms was influenced by the change of these environmental factors with different vegetable planting ages.

Conclusions The continuous vegetable cultivation has significantly increased the soil salt contents, led to nutrient unbalance and soil acidification. The changed soil properties have caused the variation of soil bacteria and fungi population, and consequently caused the gradual increase in total soil nematodes and the ratio of plant parasite nematode to predator nematodes, especially the significant increase in the ratio of Meloidogyne. In the tested suburbs of Beijing, the highest degree of soil disturbance and the weakest soil micro-ecology is in the field under 12 years’ vegetable production in the suburb of Beijing.