Effects of Missing Hole-seedling Between Plants and Rows in Mechanical Transplanting of Rice Seedlings on Agronomic Traits

【Objective】 Mechanical transplanting of rice seedlings often results in some holes being missed for the transplantation. Understanding their ultimate consequence for yield and yield components is important to help improve design and implementation of mechanical transplanting. The purpose of this paper is to experimentally study the effect of the types and number of such missing holes on yield and yield components of rice of different varieties. 【Method】 Rice varieties of Kongyu 131 (KY131) and Longjing 31 (LJ31) were used as the model plants in the experiment. For each variety, there were two missing hole-seedling treatments: inter-plant (P) and inter-row (R). For the inter-plant missing, there were further three types of missing: independent type (PI), spaced type (PS) and mixed type (PM), while for the inter-row missing, there were relative type (RR), reciprocal type (RP), and mixed type (RM). For each treatment, we measured yield and yield traits of rice. 【Result】 There were significant differences in effective panicle numbers, seed setting rate, harvest index and grain yield between the two varieties and treatments. Compared with CK (without missing), the treatments reduced the effective panicles, grain numbers and yield, with the average effective panicles reduced by 13.45% and 15.44% and the average grain yield by 10.50% and 12.82%, respectively, for the inter-plant and inter-row missing holes treatments. The missing holes also changed the allocation of morphological characters of the main stem and the grain yield, though the change varies with varieties. When the number of missing holes was the same, the variation in seed setting rate of KY131 was greater than that of LJ31, and the effective panicles, grain numbers, harvest index and grain yield all decrease with the increase in the missing holes. The yield falling range of inter-row was higher than that of inter-plant, and the yield of KY131 decreases more than that of LJ31, with the average yield reduction in the former and latter being 13.01% and 10.38%, respectively, compared to CK. The main determinant of yield reduction was effective panicles and grain numbers. Correlation analysis showed a significant negative correlation between the missing holes and grain yield, with the effective panicles and 1 000-grain weight reduced being greater for KY131 than for LJ31. The number of effective panicles and grains per square meter was positively correlated with the grain yield at significant level, with the correlation coefficient for the effective panicles number being 0.954 7** and 0.890 4**, respectively, for KY131 and LJ31, the correlation coefficient for the grains number being 0.981 2** and 0.912 5**, respectively, for LJ31 and KY131. 【Conclusion】 The missing holes between plants and rows had a negative effect on many characters of rice, reduced the yield, and was not conducive to the effective combination of agricultural machinery and agronomy.