Regulatory effects of root-zone targeting irrigation on root anatomy and soil water and fertilizer transport in Nantaihutezao grapes

【Objective】Grape, as an important cash crop widely cultivated in the world, is not only the core raw material for winemaking and the fresh food industry, but also one of the key pillars of China’s agricultural industrial structure upgrading and rural revitalization strategy. Northwest China has become a core production area for high-quality grapes by virtue of its unique climatic conditions, with abundant light, significant temperature differences between day and night, and dry air. However, the frequent occurrence of extreme drought events in the region and the extremely serious problem of water shortage have exacerbated the contradiction between water supply and demand in grape growing. In order to efficiently utilize water resources, many different irrigation methods have emerged, and the main irrigation methods currently used for crops are diffuse, furrow, sprinkler, drip and seepage irrigation. Different irrigation methods have a great impact on viticulture. For this reason, it is important to study the effects of different irrigation methods on grapevines under different irrigation levels to provide theoretical support for viticulture and water- saving irrigation models in the arid regions of Northwest China.【Methods】 Two-year old Nantaihutezao grapes were used as experimental materials, four treatments were set up, namely, conventional drip irrigation (DI) (30 min, 3.6 L), 100% RTI (30 min, 3.6 L), 75% RTI (22.5 min, 2.7 L), and 50% RTI (15 min, 1.8 L), to study the water movement pattern, root vigor, root anatomy, and soil alkaline nitrogen, effective phosphorus, quick phosphorus, and soil water content of the soil in different soil layers (0-60 cm) of the different irrigation treatments. The effects of different irrigation treatments on water movement, root vigor, root anatomical structure and soil content of different soil layers (0-60 cm) were investigated.【Results】(1) The results of water movement pattern showed that under DI treatment, water was mainly concentrated in the soil surface layer (0-20 cm), while the RTI treatment led to better distribution of soil moisture content in the deeper layer than DI by directly transporting water to the distribution area of grapevine root system (near the soil layer of 20 cm), and then rapidly infiltrating downward with the water. (2) The results of root vigor showed that the root vigor under different irrigation treatments was significantly different. There was a significant difference, in which the root vigor under 100% RTI was significantly higher than that of DI, which was 1.23 times higher than that of DI; the root vigor under 75% RTI was much similar to the results of DI. (3) The results on root anatomical structure showed that the root xylem conduit density and conduit diameter produced significant changes under different irrigation treatments, in which the conduit density under 75% RTI and 50% RTI was 25% and 100% higher than that of DI, respectively, while the average conduit diameter showed the opposite trend, with the mean conduit diameters under 75% RTI and 50% RTI being 19% and 97% lower than that of DI, respectively; (4) The results on soil nutrients showed that there were significant differences in the vertical distribution of soil nutrients under different irrigation treatments. The DI treatment resulted in significant enrichment of nutrients in the 0-20 cm surface layer of the soil, where alkaline dissolved nitrogen, effective phosphorus, quick potassium, and organic matter contents were 1.54-3.10 times higher than those of the RTI treatment, but the deeper layers (30-60 cm) had lower nutrient contents than those of the RTI treatment as a whole. The RTI drove nutrients through directional water transport, and the RTI drove the nutrients to the intensive root distribution area (20- 40 cm) through directional water transport, in which the contents of alkaline dissolved nitrogen, effective phosphorus, quick-acting potassium and organic matter in the 20-60 cm soil layer under the 100% RTI treatment were 1.19-1.34 times higher than those in the DI treatment, and the contents of alkaline dissolved nitrogen, effective phosphorus and organic matter in the 20-60 cm soil layer under the 75% RTI treatment were much similar to those in the DI treatment.【Conclusion】The RTI improved the plant water and fertilizer utilization by changing the water movement pattern, affecting root vigor, optimizing root conduit structure and improving the vertical distribution of nutrients in the deep soil layer, and the mode of“reducing depletion in the surface layer and increasing storage in the deep layer”of RTI reduced the loss of nutrients caused by evaporation and runoff, and strengthened the drought-resistant ability of the plant and improved water utilization efficiency. The RTI model of“surface reduction and deep storage”could reduce the nutrient loss caused by evaporation and runoff, enhance the drought resistance of plants and improve the water utilization efficiency, which would provide a theoretical basis for the precision irrigation technology of grapevine in arid areas.