Effect of planting density on stem characteristics and yield of summer maize in the Hilly Central Sichuan Basin, China

Increasing planting density has been one of the most common ways of increasing maize yield. In order to determine the proper planting density of maize in Hilly Central Sichuan Basin (HCSB) in China, an experiment involving 5 planting densities (4.50×10⁴, 5.25×10⁴, 6.00×10⁴, 6.75×10⁴ and 7.50×10⁴ plant·hm^-2) of maize were conducted. The effects of planting density on stalk characteristics and yield of summer maize cultivar 'Zhenghong-505' were investigated. The results showed that plant height, ear height, internode length, length-to-diameter ratio of internode increased with increasing planting density. Also stem diameter, stem diameter coefficient, internode dry weight, internode dry matter weight to length ratio, stalk crushing strength (SCS) and rind penetration strength (RPS) decreased with increasing planting density. There were significant differences the traits except ear height among different planting densities. Compared with planting density of 4.50×10⁴ plant·hm^-2, RPS of the 1st, 3rd and 5th internodes reduced significantly respectively by 27.10%, 22.78% and 30.80% under planting density of 7.50×10⁴ plant·hm^-2. Maize yield increased at first and then decreased with increasing planting density, with a maximum yield under 6.00×10⁴ plant·hm^-2. There was a significant increase in yield (12.02%) under planting density of 6.00×10⁴ plant·hm-2 compared with yield under planting density of 4.50×10⁴ plant·hm^-2. Corncob length, corncob diameter, spike rate, kernel per spike and 1000-seed weight significantly (P < 0.05) decreased with increasing planting density, while the effective panicle and barren tip length significantly increased. Correlation analysis indicated that SCS was significantly positively correlated with RPS (r=0.93^**). Moreover, SCS and RPS had significantly or extremely significant positive correlation with stem diameter, stem diameter coefficient, internode diameter, internode dry weight and internode dry matter weight to length ratio. SCS and RPS had significantly or extremely significant negative correlation with plant height, internode length and length to diameter ratio. A stronger correlation was found between stalk agronomic trait and SCS. Yield per plant had significant or extremely significant positive correlation with stem diameter, stem diameter coefficient, internode diameter, internode dry weight, internode dry matter weight to length ratio, SCS and RPS. It then had significant negative correlation with internode length and length to diameter ratio. Stepwise regression analysis suggested that stem diameter coefficient and internode dry matter weight to length ratio had the most significant influence on SCS. It was concluded that planting density was the primary factor influencing maize stalk characteristics and yield. An appropriate increase in planting density significantly increased maize yield. Then stem diameter coefficient and internode dry matter weight to length ratio were important agronomic indexes for evaluating lodging resistance of maize stalk.