Mechanism behind densification and yield increase of spring maize with different density-tolerance regulated by subsoiling

Abstract: In order to explore the effect mechanism of subsoiling on density-tolerance of maize varieties, and provide a scientific basis for increasing density and improving production in Inner Mongolia plain irrigation area by subsoiling measures. This study was implemened in the three major plain irrigation districts of Inner Mongolia. Different density tolerant spring maize varieties were used as test materials, Denghai 618 (DH618, density tolerant ) was planted in the irrigation areas of Hetao Plain and Tumochuan Plain, Nonghua 101 (NH101, density tolerant) in the irrigation area of Xiliaohe Plain, and Jingke 968 (JK968, density sensitive) in the irrigation area of above three plains. In the experiment, we set up 5 planting density gradients (45 000, 60 000, 75 000, 90 000 and 105 000 plants/hm2) under subsoiling and shallow rotation tillage conditions, respectively, and determined and analyzed the indexes of configuration characteristic of root system, canopy physiological characteristics, yield and yield components. The results showed that subsoiling measures improved soil water content in 0-80 cm, and reduced soil compaction. Compared to shallow rotation, the root length and dry weight of maize significantly increased under subsoiling condition. Meanwhile, SPAD value, leaf area index (LAI) and dry matter per plant were too obviously improved, especially in late growth stage. From spinning to milk-cooking, the reduction extent of density tolerant varieties leaf SPAD was decreased from 6.8- 10.1 to 6.3-8.9, and that of density sensitive varieties was reduced from 7.6-10.9 to 7.1-10.1. The decreasing range of density tolerant varieties LAI was changed from 0.45-1.32 to 0.43-1.23, and that of density sensitive varieties was decreased from 0.45-1.32 to 0.43-1.23. Subsoiling effectively delayed senescence, prolonged photosynthetic time, alleviated the decline rate of dry matter accumulation per plant with density increasing, and improved the density tolerance of maize. Finally, yields of different density tolerant spring maize varieties were increased under various planting densities, and achieved the effect of increasing density and yield. The responses of different density-tolerant varieties to subsoiling were different. Subsoiling made the planting density of density tolerant varieties reaching the highest yield to increase from 82 800-96 200 to 86 800 -112 000 plants/hm2, and the highest yield improved from 13.22-13.81 to 13.88-14.89 t/hm2. However, the planting density of density sensitive varieties increased from 81 600-89 000 to 81 700-96 200 plants/hm2, and the highest yield increased from 13.2 -14.30 to 13.83-14.80 t/hm2. Yield and planting density was fitted with "linear + platform". The results showed that the density tolerant varieties could increase 7 900 plants/hm2 with yield by 1.37 t/hm2, while the density sensitive variety could increase 6 000 plants/hm2 with yield by 1.06 t/hm2 through subsoiling measure. Variance analysis of maize plant characters responsing to subsoiling in three plain irrigation in three plain irrigation areas showed that the root length, root dry weight, LAI, group dry matter quality and yield of maize shoots were significantly (P< 0.05) different in different ecological regions. Path analysis of plant indices with ecological factors indicated that the main ecological factors of causing interregional differences in subsoiling effect were mainly determined by the after anthesis day temperature difference <10℃, the after flowering sunshine duration <8 h, the after flowering anthesis average temperature and the content of soil available phosphor. The deep loosening effect of density tolerant varieties was more stable among regions.