The response of roots and the rhizosphere environment to integrative cultivation practices in paddy rice

Integrative cultivation practices (ICPs) are essential for enhancing cereal yield and resource use efficiency. However, the effects of ICP on the rhizosphere environment and roots of paddy rice are still poorly understood. In this study, four rice varieties were produced in the field. Each variety was treated with six different cultivation techniques, including zero nitrogen application (0 N), local farmers' practice (LFP), nitrogen reduction (NR), and three progressive ICP techniques comprised of enhanced fertilizer N practice and increased plant density (ICP1), a treatment similar to ICP1 but with alternate wetting and moderate drying instead of continuous flooding (ICP2), and the same practices as ICP2 with the application of organic fertilizer (ICP3). The ICPs had greater grain production and nitrogen use efficiency than the other three methods. Root length, dry weight, root diameter, activity of root oxidation, root bleeding rate, zeatin and zeatin riboside compositions, and total organic acids in root exudates were elevated with the introduction of the successive cultivation practices. ICPs enhanced nitrate nitrogen, the activities of urease and invertase, and the diversity of microbes (bacteria) in rhizosphere and non-rhizosphere soil, while reducing the ammonium nitrogen content. The nutrient contents (ammonium nitrogen, total nitrogen, total potassium, total phosphorus, nitrate, and available phosphorus) and urease activity in rhizosphere soil were reduced in all treatments in comparison with the non-rhizosphere soil, but the invertase activity and bacterial diversity were greater. The main root morphology and physiology, and the ammonium nitrogen contents in rhizosphere soil at the primary stages were closely correlated with grain yield and internal nitrogen use efficiency. These findings suggest that the coordinated enhancement of the root system and the environment of the rhizosphere under integrative cultivation approaches may lead to higher rice production.