Objectives Continuous planting of cowpea would cause reduced yield, deteriorated quality and low economic benefit. Effects of growth and rhizosphere soil properties by celery and gynura bicolor as companioncrops of continuous cropping cowpea were studied to provide a theoretical basis for alleviating continuouscropping obstacles of cowpea.
Methods A pot experiment was conducted using the cowpea continuous cropping soil. There were three treatments, cowpea monoculture (control), celery and cowpea intercropping, and gynura bicolor and cowpea intercropping. Growth index, soil microbial quantity, soil physical and chemical property, chlorophyll content, antioxidant enzyme activity and yields in different treatments were investigated.
Results Compared with the monoculture control, the plant heights, stem diameters, fresh and dry weights of cowpea were significantly increased by 23.98%, 9.07%, 16.14% and 16.00% in the celery treatment, respectively; while the plant height and stem diameter were not increased significantly, and the shoot fresh and dry weights were significantly decreased in the bicolor treatment. The actinomyces population was significantly increased by 10.06%, but the fungi population was significantly decreased by 41.51% in the soils of celery treatment. There was no significant difference in the population of bacteria between celery treatment and control, nor in the population of actinomycetes, fungi and bacteria between the bicolor treatment and the control. The activities of soil urease, invertase, polyphenol oxidase and acid phosphatase were the highest, and were increased by 7.07%, 381.00%, 21.63% and 42.79% in bicolor treatment, and the activities of invertase, polyphenol oxidase and acid phosphatase and acid phosphatase were significantly increased by 162.48%, 30.75% and 35.27% in the celery treatment, respectively, while the urease activity had not been impacted significantly. The soil pH were significantly increased 0.98% and 1.23% of the accompanied celery and gynura bicolor treatments, while the soil conductivity were prominently decreased by 9.48%, 8.34% in the treatment of celery and biocolor, respectively. The contents of chlorophyll a, chlorophyll b and chlorophyll a+b of cowpea in celery treatment were significantly higher than in the other ones, and there were no significant differences between the later treatments. The activities of peroxidase (POD), glutathione reductase (GR) and dehydroascorbate reductase (DHAR) of cowpea in the celery treatment were the highest, and were significantly increased by 16.20%, 73.49% and 17.76%, respectively, while the catalase (CAT) activity was slightly affected in the celery treatment. The activities of CAT and GR of cowpea in the bicolor treatment were significantly higher than those in control, which were increased by 97.12% and 58.79%, while the activities of POD and DHAR were not be affected significantly. The celery and bicolor treatment significantly improved the yield of cowpea, with increment of 19.87% and 19.61% at the early stage, 18.22% and 15.33% at the middle stage and 8.44% and 12.70% at the later stage.
Conclusions The accompanied growth of celery and gynura bicolor with continuous cropping cowpea could improve leaf antioxidant enzyme activities and rhizosphere soil enzyme activities, improve the rhizosphere environment and microbial structure, as a result, alleviate the effect of continuous cropping obstacle. Celery performs better than gynura bicolor, so should be recommonded.
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