Seasonal drought during winter and spring is a significant factor limiting the number of fertile spike and grain yield of wheat in Southwest China. This study investigated the combined effects of straw mulching and 16, 17-Dihydro gibberellin on tillering in wheat, spike formation, and grain yield of dryland wheat, which would enrich the theoretical framework of tillering and spike formation regulation, and provide a theoretical basis for stable and high yield of wheat in the dryland farming system.

The experiment was conducted from 2022 to 2024 at the Renshou experimental station, which is a typical hilly dryland farming system in Southwest China. The straw mulching (SM, straw mulching with no-tillage; NSM, no straw mulching) and 16, 17-Dihydro gibberellin (DHGA₁₀₀, spraying exogenous 16, 17-Dihydro gibberellin A₅ at the three-leaf stage; DHGA₀, spraying water at the three-leaf stage)，In view of the current situation that soil drought in the hilly and dryland of Southwest China inhibits wheat tillering and spike formation, resulting in insufficient fertile spikes of wheat, the effects of straw mulching and 16, 17-Dihydro gibberellin A₅ on wheat tillering, matter accumulation and endogenous hormone content were analyzed, exploration treatments were employed to evaluated their combined effects on the tillering and grain yield of dryland wheat.

Compared with no mulching, straw mulching increased the fertile spikes and grain yield of wheat by 13.16% and 20.64%, respectively; DHGA₁₀₀ applicated at the three-leaf stage increased the fertile spikes and grain yield of wheat by 9.7% and 14.37%, respectively, compared with no DHGA₀ application. Straw mulching combined with DHGA₁₀₀ extended the effective tillering period, promoted the occurrence of the first tiller (T1 tillers), and increased the tillering capability and tillering emerging rate of T1 tillers, ultimately increasing fertile spikes and grain yield. Compared with NSM, SM increased the tillering ability, tiller emerging rate, and fertile spikes by 46.02%, 21.21%, and 13.41%, respectively; DHGA₁₀₀ increased these parameters by 22.56%, 16.18%, and 9.72%, respectively, compared with DHGA₀. For every 0.1 increase in tillering ability per plant, the number of fertile spikes increased by 2.84%; for every 0.1 increase in tillering survival rate of tillers after stem extension, the fertile spikes increased by 19.3%; for every 10% increase in tiller emerging rate of T1 tillers, the fertile spikes increased by 14%. Both straw mulching and DHGA could regulate the endogenous hormone levels in tillers and increase the proportion of tiller dry matter to total plant dry matter. Compared with NSM, SM increased the ratios of ZR/ABA and GA₃/ABA in tillers by 52.66% and 38.68% and decreased the ratio of IAA/ABA by 11.10%. Under SM treatment, DHGA₁₀₀ increased these ratios by 14.06%, 21.67%, and 31.67%, respectively, compared with DHGA₀.

Exogenous 16, 17-Dihydro gibberellin A₅ applicated to straw mulching at the three-leaf stage promoted the occurrence and spike formation of T1 tillers via ABA/GA signaling, thereby increasing fertile spikes and grain yield of wheat. Therefore, the combination of straw mulching (8 000 kg·hm^-2) with the application of 16, 17-Dihydro gibberellin (100 mg·L^-1) at the three-leaf stage was a promising approach for high and stable grain yield of wheat in the dryland farming system.

Frequent drought in winter and spring as well as excessive application of nitrogen limited wheat yield and sustainable development in rainfed farming areas of dryland in southwest China. The objective of this study was to clarify the effects of straw mulching from autumn fallow and reducing nitrogen application on root distribution, wheat yield, water and nitrogen utilization of dryland winter wheat, so as to provide a basis for optimizing wheat tillage system and green, high quality and efficient production of winter wheat in dryland of Sichuan province.

The experiment was carried out at Renshou experiment station of Sichuan Agricultural University in Sichuan province from 2016 to 2018. The spilt plot design was employed with main plot of maize straw mulching (mulching from autumn fallow to wheat harvesting: SM) and no mulching (NM), and sub-plot of different nitrogen application rates (N₀: 0; reducing nitrogen rate (RN): 120 kg N·hm^-2, and conventional nitrogen rate (CN): 180 kg N·hm^-2). Soil moisture, root length, root distribution, wheat yield, water consumption (ET), water and nitrogen use efficiencies were investigated.

Compared with NM, SM significantly increased the soil water content in 0-10 cm and 10-20 cm layers from sowing to booting stage and the soil water storage in 0-100 cm layer at sowing and jointing, and the soil water retention effect of straw mulching lasted until booting and anthesis stage. SM also promoted the wheat root growth at jointing and anthesis stage with higher root diameter and significantly higher root length density in 0-10 cm layer. The mean values of total ET, WUE (water use efficiency), nitrogen accumulation amount of wheat plant, nitrogen accumulation rate from sowing to jointing, nitrogen accumulation rate from jointing to anthesis, nitrogen use efficiency for grain production (NUEg), agronomic efficiency of nitrogen fertilizer (AEN), nitrogen fertilizer partial factor productivity (NPFP) and wheat yield under SM increased by 11.4%, 71.8%, 73.1%, 119.0%, 100.0%, 3.6%, 264.7%, 78.2% than that under NM, respectively, and the recovery efficiency of nitrogen fertilizer (REN) under SM increased by 44.4 percentage points compared with NM. The wheat yield under SM increased by 92.9% because of the significantly increased average spike number (31.8%) and grains per spike (44.4%). The effect of straw mulching was greater than that of nitrogen application. Compared with CN, RN did not significantly decrease the wheat root length density, ET, WUE and wheat yield. Combining with SM, RN significantly improved the NUEg, physiological efficiency of nitrogen (PEN), AEN, NPFP, and REN.

Straw mulching from autumn fallow improved soil water content and storage and optimized root distribution in 0-10 cm layer with higher root length density and root diameter, thus to increase the nitrogen absorption and utilization, wheat yield, and the utilization of water and fertilizer. Straw mulching combined with 120 kg N·hm^-2 was a high yield cultivation mode with reducing nitrogen application and high water and nitrogen use efficiency for dryland winter wheat in Sichuan province, China.

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.