Effects of mechanical tillage and sowing methods on photosynthetic production and yield of wheat in rice stubble

The heavy and sticky soil after rice planting and the increasing rice straws returned into field have restricted subsequent wheat growth in the region along the Huai River. An effective way is to combine the tillage and seeding operation. This study aims to propose the optimal combination of mechanical tillage and seeding for wheat following rice. A field experiment was conducted from 2017 to 2019 in Sihong County, Jiangsu Province, China, in order to investigate the effects of tillage and seeding mode on the formation of spike number and single spike weight, photosynthetic production, and yield of wheat. The tillage included the plow tillage followed by rotary tillage (PR) and the no-tillage (NT). The seeding included medium-size strip seeding, medium-size drill seeding, small-size strip seeding, and small-size drill seeding. The measurement indexes were the number of stem and tiller, leaf area and dry matter accumulation at the main stages, the net photosynthetic rate at the anthesis and milk-ripe stage, tiller fertility, and grain yield. The results showed that: 1) The number of stem and tiller, as well as leaf area index during the whole growth stages, and the leaf area of single stem and net photosynthetic rate of flag leaf at the anthesis and milk-ripe stages were higher under the NT treatment than those under the PR treatment. The weight of a single spike increased by 17.2% and 15.5% in the two seasons under the NT, compared with the PR. 2) The tillage significantly (P<0.01) affected tiller fertility. Compared with the PR, the accumulation of dry matter during maturity and post-anthesis stages under the NT treatment were higher by 34.2%, and 42% in 2018, while 23.3%, and 75.3% in 2019, respectively. The grain yield under NT was higher than that under PR by 25.4% in 2018, and 15.2% in 2019. 3) In medium-sized mechanical seeding, the crop was facilitated to well use the nutrient and solar-thermal resources during the whole reproductive period, indicating a high photosynthetic capacity of flag leaf and strong material production. The application of medium-size seeders achieved a much higher grain yield in 2018 and 2019, compared with small-size seeders, without significant difference (P>0.05) under the NT treatment in 2018. Compared with the drill seeding, strip seeding improved the individual growth space of wheat, the leaf area, as well as the capacity production and transformation of dry matter. Moreover, the increase of spike number and total biomass was attributed to the strong vigor seedlings before the overwintering stage, early emergence with the rapid growth of tillers, and tiller fertility. A large photosynthetic area of individual leaf and canopy leaves with slowly decreasing leaf area index and improved photosynthetic capacity after the anthesis promoted the rapid accumulation of post-anthesis dry matter, the single spike weight, and grain yield. In the NT condition, the medium-size strip seeding was expected as a sustainable and effective practice to improve the growth and grain yield of wheat following rice in the Huai River plain. The findings can provide a further theoretical basis for the optimal selection of combined tillage and seeding in wheat production following rice.