Effects of mechanical dry direct seeding ways on rice yield and photosynthetic material production characteristics

Mechanical dry direct seeding has gradually been favored, with the continuous advancement of agricultural mechanization. This study aims to explore the impact of different mechanical dry direct seeding on rice yield. Taking 9108 variety as the test material, the rice and wheat crops were collected in the middle and lower reaches of the Yangtze River. The experiment was set the "dual-axis rotary tillage (20 cm tillage depth), controlled depth sowing, and two times of suppression" dry direct seeding (DDS-1), "one-time rotary tillage (tillage depth of 17 cm), and 7.5 cm precision. There were three mechanical dry direct seedings, namely, "uniform sowing" (DDS-2), "one-time rotary tillage (15 cm depth), and one-time suppression" dry direct seeding (DDS-3), with the water direct seeding (WDS) and blanket seedling planting (MT) as the control. The fertilizers used in each treatment were the same, where the pure nitrogen 270 kg/hm2 was applied, and the form of quick-acting urea and controlled-release nitrogen fertilizer was 40 d and 100 d once. The mixing ratio (pure nitrogen) of quick-acting urea and controlled-release nitrogen fertilizer for 40 days and 100 days was 5:1:4, and the phosphate fertilizer and potassium fertilizer were all applied on a one-time basis using a fertilizer thrower before sowing or transplanting, where the application P2O5 was 135 kg/hm2, and K2O was 240 kg/hm2, according to the field operation requirements and agricultural time consumption of various local planting. The appropriate sowing period for each planting was designed, and the water supply was fully provided for the rice yield potential of each planting. A systematic comparison was implemented to clarify the effects of different mechanical dry direct seeding on the rice yield and photosynthetic production characteristics. The results showed that the yield of DDS-1 increased by 3.42%-4.47% and 5.10%-5.45%, respectively, compared with DDS-2 and DDS-3. The yield of mechanical dry direct seeding presented a decreasing trend, compared with the water direct seeding and machine inserting. There was no significant difference between the DDS-1 and WDS. The emergence rate and seedling rate of DDS-1 increased under different mechanical dry direct seeding, indicating the improved quality of seedling emergence. The DDS-1 increased the total dry matter accumulation at the maturity and the dry matter from heading to maturity, compared with the DDS-2 and DDS-3. The cumulative amount increased the leaf area index, population growth rate, photosynthetic potential, and net assimilation rate at the grain-filling stage. The appropriate effective panicle number remained to increase the number of grains per spike, the number of spikelets in the population, and the seed setting rate. To sum up, under the condition of returning the full amount of straw to the field in the rice-wheat double-cropping area, the selection of the appropriate mechanical dry direct seeding was beneficial to the early emergence and seedling formation of rice, thus increasing the number of grains per panicle and the number of spikelets in the population, as well as the growth rate of rice. The late photosynthetic production capacity eventually promoted the increase of the yield of dry direct seeding rice. The production capacity in the middle and late stages of rice growth finally promoted the yield of dry direct seeding rice.