Effect of intercrop of maize || white clover on maize photosynthesis, yield, and soil respiration with different row spacing in a Karst area

To explore the effect of maize || white clover intercropping under different row spacing in the Karst area of Guizhou, maize || white clover intercropping and a corn monoculture were grown using 30, 50, and 70 cm row spacing. Photosynthetic characteristics, maize ear characters, yield, and rhizosphere soil respiration were monitored. The results showed that except for the 50 cm row spacing treatment, the diurnal variation in the photosynthesis rate of maize leaves in each test group and control group exhibited a double peak curve. The lowest daily mean of intercellular CO₂ concentration in maize leaves, the highest utilization rate of CO₂, and the highest daily average photosynthetic rate were under the 50 cm row spacing treatment. Under this treatment, the corn yield was significantly increased (P < 0.05). Line spacing processing of 30 and 50 cm increased the fresh straw yield, and the whole plant total yield significantly increased (P < 0.05). Corn yield, fresh straw yield, and total yield of whole plants were the lowest in the 70 cm row spacing treatment (P < 0.05). Different treatments had no effect on stomatal conductance, transpiration rate, grain number on the cob, and ear length (P > 0.05). The effects of intercropping on soil respiration inhibition was not obvious; however, different row spacing planting modes influenced soil respiration. The 30 cm row spacing planting mode had the best effect on soil respiration inhibition, which reduced carbon emission, followed by the 50 cm row spacing planting treatment. Therefore, 30 cm or 50 cm row spacing maize || white clover intercropping was the most suitable for harvesting fresh straw in the Guizhou Karst area. The 50 cm row spacing maize || white clover intercropping was the most suitable when corn seeds or seed and straw were harvested at the same time.