Maize-Soybean Intercropping Interactions Above and Below Ground

Above-ground and below-ground interactions of the maize-soybean intercrop were studied in a 2-yr field experiment with measurements of grain and total biological yield; N, P, and K uptake; and photosynthesis. Four intercrop treatments included no shoot or root separation (T1), shoot and root separation (T2), root separation (T3), and shoot separation (T4); two controls were solo maize (T5) and solo soybean (T6). Results indicated that competition between above-ground and/or below-ground plant parts is a key factor in describing intercropping advantage, and that intercropping is not advantageous in the absence of competition. Specific results showed significant intercrop advantages when roots and shoots were not separated, the differences between component species in above-ground and below-ground competition, and a greater contribution to intercrop advantages from below-ground interactions than above-ground interactions. Although competition for nutrients, water, and sunlight is the primary explanation often used to explain intercrop advantages, our results indicate that competition for nutrients was of more importance than competition for sunlight. Differences in nutrient uptake data were closely related to those of yields, confirming the importance of below-ground competition. Relatively less competition above ground was confirmed by minimal differences in photosynthesis among treatments. More refined studies of resource competition could further confirm the different contributions of above-ground and below-ground interactions. One potential application of results could be their use in intercrop systems modeling.