Competition and yield in intercrops of maize and sunflower for biogas

Maize (Zea mays L.) is widely used for the production of biogas, but intercrops of maize and sunflower (Helianthus annuus L.) might improve yield as well as the environmental compatibility of biofuel production. We conducted a field study planting both crops in pure stands and intercrops in three intercropping ratios (maize:sunflower with 33:67, 67:33 and 50:50 ratio) at two nitrogen application rates (no fertilizer and 85 kg N/ha as organic fertilizer plus 85 kg N/ha as mineral fertilizer) to determine the competition between the two species and the advantage of intercropping systems at two sites differing in water supply during 2007 and 2009. Dry matter yield of maize and sunflower in mono- and intercropping systems were significantly affected by intercropping ratio, nitrogen fertilizer rate and environments. Sunflower was more competitive than maize especially in intercrops with 67% sunflower. Intercropped sunflower had a higher relative crowding coefficient (K = 1.39) than intercropped maize (0.86). Intercropping with 67% maize had the highest land equivalent ratio (1.11) and relative methane yield advantages (0.94) in one environment and showed high yield stability. It is concluded that the maize component should be dominant (>50%) for intercropping. In regions with more rainfall during the growing season, maize–sunflower intercrops required a sufficient N supply to realize a yield advantage.

► Sunflower was more competitive than maize in intercrops with 67% sunflower.
► Intercropping with 67% maize had the highest land equivalent ratio.
► Intercropping with 67% maize showed high yield stability.
► In regions with more rainfall during the growing season, maize–sunflower intercrops required a sufficient N supply to realize a yield advantage.
► Specific methane yield for maize was higher than for sunflower.