Effects of line-spacing expansion and row-spacing shrinkage on canopy structure and yield of spring corn

To explore the physiological and ecological mechanisms of expanding line-spacing and shrinking row-spacing for increasing planting density and yield of spring corn in Xiliaohe Plain, a study was conducted with two corn varieties (the compact density-enduring variety 'Nonghua 101' and the semi-compact variety 'Weike 702') with planting densities of 6×10⁴ plants·hm^-2 (D1), 7.5×10⁴ plants·hm^-2 (D2) and 9×10⁴ plants·hm^-2 (D3). Then the conventional cultivation was used as the control treatment (CK) with row-spacing of 60 cm and plant-spacing of 27.78 cm (D1), 22.22 cm (D2) and 18.52 cm (D3). The expanding line-spacing and the shrinking row-spacing mode of cultivation (KH) had row-spacing of 100 cm and plant-spacing of 16.67 cm (D1), 13.33 cm (D2) and 11.11 cm (D3). The leaf area index, stem leaf angle, leaf orientation value, light transmittance of corn canopy at spinning stage, milk-ripe stage and full ripe stage and component factors of yield were determined, and also leaf area attenuation rate was calculated. Then the effects of expanding line-spacing and shrinking row-spacing on spring corn yield and canopy structure were determined. The results showed that the yields of KH treatments were significantly higher than that of CK treatments, where the yield increased most obviously under D2 density. Leaf area index of KH was higher than that of CK at late growth stage, and reached the highest value at milk-ripe stage with the most obvious variation under D2 density. Stem leaf angle of the upper leaves was smaller and with higher leaf orientation value than those of the lower ones. Stem leaf angle of middle and lower leaves were larger but with smaller leaf orientation values than those of the upper ones for 2 varieties under KH treatments. The light transmittances of canopies were higher than those of CK for both varieties under KH plantation mode. For D1 density, light transmittances of canopies of 'Weike 702' was in the order of top layer > spike layer > bottom layer, except in 2015. Under the D2 and D3 densities, light transmittances of canopies of 'Weike 702' was in the order of spike layer > top layer > bottom layer. The differences were most obvious under D2 density, except in 2015. In conclusion, canopy structure of KH planting pattern was more reasonable under higher planting density resulting in higher yield. The responses of different varieties to KH planting pattern were different. Leaf area index and stem leaf angle of 'Nonghua 101' were lower than those of 'Weike 702'. Leaf aspect and canopy transmittance were also higher than those of 'Weike 702'. Measured yields of 'Nonghua 101' under different densities were higher than those of 'Weike 702', and the highest yield was under the 7.5×10⁴ plants·hm^-2 planting density. Moreover, yield increase of 'Nonghua 101' was more obvious than that of 'Weike 702'.