Effects of Straw Mulching and Nitrogen Application on the Improvement of Wheat Root Architecture and the Absorption and Utilization of H⁺ and NO₃^- in Hilly Dry Land

In order to further study the root architecture and root tip nitrogen transport process of wheat after straw mulching in the wheat-maize rotation system in the dry land of southwest China, and to elucidate the physiological basis of straw mulching and nitrogen application to promote the efficient absorption and utilization of wheat nitrogen.

The experiment was a two-factor split plot experiment of straw mulching (SM: straw mulching; NSM: no straw mulching) and nitrogen application (N0: 0; N1: 120 kg·hm^-2), which was conducted at Sichuan Renshou Modern Agricultural Test Station from 2020-2022. The effects of straw mulching and nitrogen application on soil physicochemical properties, wheat root architecture, nitrogen absorption in root tips, plant biomass and aboveground nitrogen accumulation and utilization were analyzed according to the current situation that soil drought inhibited root elongation in dry land of southwest hills, resulting in low wheat biomass and nutrient use efficiency.

The soil nitrate nitrogen content of straw mulching treatment increased by 43.1% and 30.8%, and the ammonium nitrogen content increased by 21.8% and 18.8%, respectively, in 2020-2021 and 2021-2022 compared with the no straw mulching treatment. Straw mulching increased the root length, root surface area, and root volume of the 0-10 cm soil layer at jointing stage, booting stage and anthesis stage of wheat, and nitrogen application significantly increased the 0-10 cm soil root length, root surface area and root volume. In addition, straw mulching and nitrogen application could significantly increase the absorption rate and net absorption rate of H⁺ and NO₃^- at the root tips of wheat, and reduce the H⁺ efflux rate at the root tips of 0-20 cm soil layer. Straw mulching and nitrogen application significantly increased the activities of nitrate reductase and glutamine synthetase in roots, and the nitrogen accumulation and biomass in the aboveground part of wheat increased by 25.8% and 35.8% on average, respectively, in two years. H⁺ absorption rate, NO₃^- absorption rate, nitrate reductase activity, glutamine synthetase activity, and nitrogen accumulation were positively correlated with root length, root surface area and root volume of 0-10 cm soil layer (P<0.05).

In the southwest hilly dry land wheat-maize rotation system, maize straw mulching and nitrogen application can increase the content of inorganic nitrogen in the soil during the wheat season, the root distribution in the soil surface and the absorption rate of H⁺ and NO₃^- at the root tips, promote nitrogen uptake and root tip nitrogen transport, and then promote aboveground nitrogen assimilation and accumulation; Under the conditions of this experiment, straw mulching combined with 120 kg N·hm^-2 is a green production mode suitable for high yield and high nitrogen use efficiency in Sichuan hilly dry land.