Abstract:
Abstract: The objective of the study was to explore the effects of seeding date and variety on the growth characteristics of mechanical transplanted rice in the rice-wheat cropping system in the rice area of southern Henan. Taking 5 rice varieties i.e. conventional medium-maturing medium japonica rice variety, conventional and hybrid late-maturing medium japonica rice varieties, conventional early-maturing late japonica rice variety and hybrid late-maturing medium indica rice variety as experimental materials, sowing experiments were carried out. The effects of different seeding dates on grain yield and yield components, number of stems and tillers, dry matter weight and population growth rate of mechanical planted rice were comparatively analyzed. The results showed that: 1) Within the set range of seeding date in the experiment, average yield of mechanical planted rice showed very significant difference among different sowing dates and varieties (P<0.01), but no significant difference between different years. This was particularly evident for the yield of hybrid late-maturing medium japonica rice variety (10.44 t/hm2) that was 9.20%-17.53% higher than the other 4 varieties (P<0.01). The output of conventional medium-maturing medium japonica rice variety was the highest in the second sowing period (on May 16) and subsequently showed a gradual decrease. The yields of other rice varieties were all the highest in the first seeding period (on May 11), and showed a trend of gradual decline with the delayed seeding date (P<0.01), but the decrease amplitudes were different among different rice varieties and sites. 2) In different yield components of mechanical planted rice, the difference of seed setting rate was not significant between the years but very significant for different sowing dates and varieties, while the differences of other yield components were all very significant for different years, sowing dates and varieties (P<0.01). The seed setting rate of conventional medium-maturing medium japonica rice variety slowly increased at first and then decreased significantly since the second sowing data, but the yield components of other rice varieties such as panicle number, number of spikelets per panicle, total spikelets, seed setting rate, 1000-grain weight all showed a significant (P<0.05) or extremely significant (P<0.01) declining trend. Different seeding dates had a significant influence on number of spikelets per panicle and seed setting rate, but less significant influence on 1000-grain weight and panicle number. Correlation analysis showed that the effects of yield components on the yield from high to low were as follows: number of spikelets per panicle > seed setting rate > panicle number > 1000-grain weight, and grain yield showed significant or extremely significant positive correlation with number of spikelets per panicle, total spikelets and seed setting rate, but showed negative correlation with panicle number and 1000-grain weight. Total spikelets showed an extremely significant positive correlation with number of spikelets per panicle, but showed a negative correlation with panicle number. Further path analysis showed that the rate of contribution to rice yield was total spikelets > seed setting rate > 1000-grain weight, and the rate of contribution to total spikelets was number of spikelets per panicle > panicle number. 3) With the delaying of seeding date, the number of stems and tillers showed an obvious increase at jointing stage and decreased at heading and maturity stage. Dry matter weight per stem and population, and population growth rate showed a gradual decline at jointing, heading and maturity stage depending on different rice varieties and seeding dates, but spike rate and harvest index had significant difference between rice varieties and seeding dates. Overall considering high yield and growth safety for mechanical transplanted rice, the preferred choice should be hybrid late-maturing medium indica rice variety for southern Henan, and the suitable seeding date may be delayed to May 25. The results will provide a reference for the high-yield and efficient production of different rice varieties under mechanical planting and for the choice of best possible varieties in southern Henan Province.