Effects of straw mulching in autumn and reducing nitrogen application on dry matter accumulation, seed-setting characteristics and yield of dryland winter wheat

Objectives We studied the effects of maize straw mulching and reducing nitrogen application rate on soil moisture before wheat sowing and the growth of wheat to provide a theoretical basis for efficient wheat production in dry farming area of Sichuan.

Methods Field positioning experiment was carried out at Renshou Experiment Station of Sichuan Agricultural University from 2016 to 2018. The spilt plot design was employed, the main plot was maize straw mulching and no straw mulching after harvest of maize, and the sub-plot was N application rates of 0, 120 and 180 kg/hm². The soil water storage in 0–100 cm and that in every 10 cm layer were measured before wheat sowing. The leaf area index (LAI), dry matter accumulation and translocation, chlorophyll content in wheat leaves were measured at the main growth stages after anthesis, and the yield and yield components were analyzed.

Results Compared with no straw mulching, straw mulching increased water storage in 0–100 cm deep of soil, especially in higher rainfall season. In each 10 cm layer, straw mulching increased the 0–10 cm water storage by 8.0 mm in 2016–2017 and 6.7 mm in 2017–2018, but did not increase the water storage below 10 cm layers significantly and stably. Compared to no straw mulching, straw mulching significantly improved LAI at all growth stages, and significantly slowed down the degradation of chlorophyll by improving the chlorophyll content of flag leaf, inverted second leaf and inverted third leaf of wheat plant after anthesis, as a result, significantly increased the dry matter accumulation at anthesis stage and total dry matter translocation to grain. The number of total and fertile florets, the seed-setting rate in fertile florets and total florets were significantly improved under straw mulching in both experimental years. The yield increase (92.9%) was mainly due to the increased average spike number (31.8%) and grains per spike (44.4%), respectively. Compared with N180 treatment, N120 treatment decreased the LAI, chlorophyll content of upper leaves after anthesis, and dry matter accumulation, decreased grain number per spike and grain yield of winter wheat, however, the effect of straw mulching was greater than that of N application, and the interaction of straw mulching with N120 treatment resulted in similar wheat yield with N180 treatment.

Conclusions Straw mulching after maize harvest could improve the water storage in 0–10 cm soil, which is beneficial to the vegetative growth and keeps long leaf vigor after anthesis stage, so stimulates the dry matter accumulation and seed-setting characteristics. Although reducing N input would lead to decreased growth and dry matter accumulation, the good effect of water by autumn mulching offsets the adverse impact of reducing N input on wheat growth. Therefore, the combination of straw mulching and N application rate of 120 kg/hm² should be recommended for the efficient wheat production in dryland winter wheat production areas in Sichuan.