Competitiveness of intercropped maize cultivars in the Loess Plateau, China

The competitive expression of intercropped maize cultivars with different characteristics for water, nutrient, dry matter partitioning and yield factors were studied in an experiment in the Loess Plateau region of China. To determine the competitiveness of intercropped maize cultivars with regards to growth and yield formation, two maize cultivars (compact cultivar "ZD958" and semi-compact cultivar "SD16") were intercropped in alternative rows under two densities (45 000 plants·hm^-2, 75 000 plants·hm^-2) conditions. The dynamic changes in dry matter of different plant organs, plant height, ear height, grain yield and yield components were investigated. The results showed that stem to leaf ratio (SLR) increased during vegetative growth and decreased after grain filling due to competition between cultivars. Intercropping increased SLR under low planting density, while significant decreased SLR under high planting density. This was more evident under high density intercropping, especially for "ZD958". Root to shoot ratio (RSR) limited redundant root growth, thereby saved resources. The RSR decrease was clear under intercropped treatments with significant differences between the low and high intercropping density. Two different cultivars with special morphology under intercropping conditions had root and canopy structures favorable for higher grain yield. With increasing intercropping density, spike to height ratio (SHR) and harvest index (HI) significantly increased. Meantime the decrease in SHR under low density of intercropping was more obvious than that of monocropping. Also SHR increased markedly under high intercropping density. The changes for "ZD958" were especially obvious. These evidences showed that intercropping improved the productive potential of maize. The structural factors of yield varied with significant decreases in spike length and thickness. However, the obvious shrinking of the length of bald needles suggested high grain pollination ratio. Finally, the analysis of competitive ratio (CR) showed that "ZD958" was more competitive than "SD16" under intercropping conditions. However, both "ZD958" and "SD16" showed distinct features which were mutually complementary for resources utilization. Intercrop competition was therefore an effective cultivation strategy for high productivity and beneficial competition among cultivars that increased water and nutrient use efficiency.