Effects of wheat straw returning and land preparation on rice yield and quality under mechanical transplanting

Mechanical transplanting has been the largest planting mode of rice production, particularly in the rice-wheat double cropping area. But the soil preparation of rotary tillage (ploughing) cannot fully meet the requirements of machine planting in recent years, due to the single function, high failure rate, and low tillage quality. Flat, clean and solid can be expected for the high quality of rice planting and yield. The main purpose of this study is to explore the tillage and soil preparation for the high yield and quality of machine-transplanted rice under the total wheat straw returning. The experiment was carried out in the rice growing season of 2021 and 2022. The rice variety was taken as Nanjing 5718. The straw treatment was selected as the main area, whereas, the tillage was as the sub-area. Among them, the yield of previous wheat was about 7.2 and 8.3 t/hm² in the experimental field in 2021 and 2022, respectively, where the amount values of straw were 12.9 and 15.4 t/hm², respectively. Two straw treatments were set: straw without returning to the field (S1) and straw full returning to the field (S2). The straw was removed from the field in the S1 treatment using manual harrowing. The straw was returned to the field in the S2 treatment using rotary tillage. Three tillage modes and land preparation were: integrated dryland biaxial rotary tillage (T1), dryland uniaxial rotary tillage + paddy field uniaxial rotary tillage (T2), and paddy field uniaxial rotary tillage (T3). Some parameters were then determined, including the tiller number, leaf area index, dry matter, grain yield, as well as the processing, appearance and eating quality of rice. The results showed that the rice yield increased by 4.54% to 5.45% (P<0.05) under S2+T1 treatment, compared with the S1, whereas, the rice yield decreased by 1.77% to 2.41% and 4.11% to 6.48% (P<0.05) under T2 and T3, respectively. The rice yield was ranked in the descending order of T2>T1>T3 under the S1 treatment, whereas, the order of T1>T2>T3 was found under the S2 treatment. The rice yield in T1 treatment was depended mainly on the panicles, dry matter accumulation, and harvest index. The total returning of wheat straw was reduced the amylose content, the area and degree of chalkiness for the better appearance quality, protein content, and taste value, compared with the S1. In addition, there was the increase in the peak viscosity and breakdown value of starch, as well as the gelatinization and palatability of rice under the S2. The chalkiness and the taste value were ranked in the descending order of T2>T3>T1, and T1>T2>T3, respectively. The taste value under the T1 increased by 3.36%-5.90%, 7.44%-11.30%, and 1.38%-4.65%, 6.28%-11.23%, respectively, compared with the T2 and T3. In summary, the T1 treatment was greatly contributed to synergistically improve the rice yield, appearance quality, nutritional quality, and taste value of machine-transplanted rice under the total wheat straw return. The finding can provide the data and theoretical support for the integrated single tillage under the full return of wheat straw to the field in the rice wheat double cropping area during mechanical transplanting.