Abstract:

Lodging is a major constraint to limit grain yield under increased planting density in modern maize (Zea mays L.) production. Effects of planting density on stalk mechanical and agronomic characteristics were investigated using three maize cultivars differing in lodging resistant ability,i.e. Jingke 519 (with a large spike under thinned planting density), Denghai 3719 (tolerant to high density) and Nongda 108 (a main local cultivar). Five levels of density treatment were imposed, 3.0, 5.25, 7.5, 9.25 and 12.0×104 plants ha^-1. Experiments were arranged in a split plot design with four replicates. The irrigation and fertilizer management in the experiment plot was consistent with typical agronomic practices in the local high-yield field. The results indicated that the increase of planting density would cause significant decreases in stalk crushing strength (SCS), rind penetration strength (RPS), internode diameter and dry weight (DW), percentage of dry matter and ratio of dry matter weight to length of internode (RDWL), and dramatic increase in internode length. The relationship between stalk mechanical characteristics and planting density fitted a exponential curve (y = ae^bx) significantly. The stalk mechanical characteristics were highly correlated with the agronomic characteristics. These characteristics of Jingke 519 were susceptive of the increasing planting density above 75 000 plant ha^-1, especially for these above the 4th internode was. The whole plant would have high lodging resistant ability if the dry matter accumulation was high in the 4th and above 4th internods. That the internod length enlarged slowly and diameter of internode decreased significantly with increasing plant density was an adaptability to high planting density for the resistant cultivar. When the percentage of DW of the 4th and above 4th internods was more than 7.5%, and its RDWL was more than 0.2 g cm^-1 at a week prior to anthesis, the plants would be resistant to lodging .The stepwise regression analysis revealed that the RDWL contributed positively the most to SCS and RPS. RDWL was definite as an agronomic indicator of maize stalk lodging resistant ability.

Key words: Maize (Zea mays L.), Density, Lodging resistant mechanism, Agronomic characteristics