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Rice–crayfish continuous production system offers high economic and ecology benefits, which developed rapidly in China. To investigate the effects of different mechanical transplanting methods and planting densities on rice yield and quality, Nanjing 2728 was used to determine rice growth performance under mechanically transplanted carpet seedling (MTCS) with equal row spacing (30 cm) at five spacings and mechanically transplanted pot seedling (MTPS) with wide and narrow rows (23 + 33 cm) at five spacings. The results showed that MTPS presented significantly higher rice yields than MTCS as more spikelets per panicle. Rice yields of both mechanical transplanting methods first increased and then reduced with decreasing planting density, and its highest value was obtained at 77.9 × 104 seedlings ha−1. Compared with MTCS at the same stage, rice tiller dynamics of MTPS first increased and then decreased. Additionally, its dry matter accumulation per stem at jointing, heading, and maturity stages, leaf area index, photosynthetic potential, crop growth rate, and net assimilation rate were all significantly higher relative to MTCS. For each mechanical transplanting method, dry matter accumulation per panicle, leaf area index, photosynthetic potential, crop growth rate, and net assimilation rate from the sowing to jointing stages declined with decreasing planting density, while dry matter accumulation per stem and net assimilation rate from the heading to maturity stages increased. Compared with MTCS, MTPS significantly improved rice milling and appearance quality, decreasing density was also beneficial to rice milling and appearance quality, while grain content of amylose and protein were not sensitive to both transplanting method and planting density. Consequently, MTPS with 13.8 cm plant spacing is a suitable mechanical transplanting method for Nanjing 2728 to obtain better yield and quality under rice–crayfish continuous production system.

Rice–crayfish rotation expanded rapidly in China, as it provides considerable profit and reduces pesticide application. This study investigated the impact of different mechanical transplanting methods and planting geometry on the yield and lodging resistance of an indica rice variety under a rice–crayfish rotation system in 2018 and 2019 in Hongze Lake district, using an excellent-quality variety Taoyouxiangzhan. Seedlings were mechanically transplanted using two mechanically transplanted carpet seedling (MTCS) with equal spacing (30 cm) at five spacings and mechanically transplanted pot seedling (MTPS) with wide and narrow rows (23 cm + 33 cm) at five spacings. The yield of MTPS was 8.3% higher across 2 years under the most optimum density than MTCS using the same density, mainly due to a significantly increased number of spikelets per panicle. Accompanied by the decrease in planting density, rice yield first increased and then decreased under each mechanically transplanting method, and reached the maximum in the A4 and B4 treatments (63.9 × 104 seedlings ha−1), respectively. Compared with MTCS, MTPS significantly increased the fresh weight of single stem, plant height, gravity center height, ear weight, length and area of the upper three leaves, so as to increase the bending moment at basal internodes by whole plant (WP), while it also increased the stem diameter, wall thickness and stem and leaf sheath dry weight per unit length of the second internode at the base, resulting in a significant increase in the force applied to break the base segment (F) and the bending moment of whole plant (M). The higher increase percentage in M than WP led to a decreased lodging index. The lodging index of both mechanically transplanting methods reduced with declined planting density in virtue of the improved breaking load of the basal internode, and it was primarily a result of increased stem diameter, wall thickness and plumpness of basal internode. The balance between the high yield and lodging resistance of Taoyouxiangzhan under a rice–crayfish rotation system can be realized at 63.9 × 104 seedlings ha−1, with MTCS at 15.7 cm plant spacing and MTPS at 16.8 cm. Generally, MTPS showed obvious advantages in yield and lodging resistance than MTCS.

The rice–crayfish continuous production system developed rapidly due to its high economic benefits and eco-friendly nature in China. This study explored the effects of mechanically transplanted methods and planting geometry on the relationship between rice yield and canopy structure, under rice-crayfish rotation using excellent-quality indica rice, and carried out in 2018 and 2019. Three mechanical transplantation methods were set as follows: carpet seedlings mechanically transplanted with 30 cm equal row spacing (CMTE), pot seedlings mechanically transplanted with narrow row spacing with alternating 23 cm/33 cm wide row spacing (PMTWN), and equal row spacing at 28 cm (PMTE). Different plant spacings (CMTE1-CMTE6, PMTWN1-PMTWN6, PMTE3, and PMTE4) were set in accordance with different mechanical transplanting methods. CMTE and PMTWN both included six transplanting densities, while PMTE included 2 transplanting densities. Results showed that rice yield was improved by 2.87–6.59% under PMTWN when compared to CMTE, which was mainly due to the increase in spikelets per panicle and filled-grain percentage. Dry matter accumulation was increased and larger leaf area indexes were observed under PMTWN than CMTE at the rice main growth stage. Yield of CMTE and PMTWN treatments increased at first and then declined with decreased planting density. Under suitable planting density, PMTWN could optimize rice population structure and increase rice yield compared with PMTE. For tested rice variety, pot seedlings were mechanically transplanted alternating alternating 23 cm/33 cm wide row spacing, combined with a plant spacing of 16.8 cm, was proper for its yield improvement under rice-crayfish rotation.