Comparison Studies Between Mulberry/Soybean And Mulberry/Millet Intercropping On Interspecific Facilitation

The plant interspecific relations in agroforestry system are more complex. It is generally considered that intercroppings between non leguminous and legume plants can have obvious interspecific facilitation of positive interaction, but intercroppings between non leguminous plants or between legume plants shows that interspecific competitiont is greater than the interspecific facilitation. This hypothesis has long affected agroforestry systems and its management. Salinity and drought in Northwest region of Heilongjiang Province in China limit agricultural and forest production, agroforestry system of intercropping between mulberry and grain crops has become a new planting pattern to bring economic development in this region. Many intercropping patterns, for example, mulberry and soybean, red bean, mung beans, beets, peas, corn and Chinese herbal medicine had developed. It was found that the intercropping between mulberry and leguminous plants has obvious interspecific facilitation in previous works of our lab. But interspecific facilitation in intercropping systems between mulberry and non leguminous plants whether has or not? In this paper, it was conducted to investigated interspecific facilitation and competition in agroforestry intercroppings of mulberry/soybean and mulberry/millet. The objects were, on one hand, to discuss photosynthetic and growth characteristics in aboveground of two intercropping patterns during cogrowth, including root growth, soybean rhizobium and nutritional characteristics of belowground in order to clarify interspecific facilitation in the systems; on the other hand, to investgate changes in rhizosphere enzyme activity and soil microorganism in intercropping systems during cogrowth. The results and conclusion were followings:1. There were more soil microorganism(Bacteria, fungi, actinomycetes)in rhizosphere of mulberry/soy be an intercropping than that of monoculture using root separation test, soil enzyme activities in rhizosphere (sucrose enzyme, phosphatase, catalase, urease) were higher than that of monoculture. Available phosphorus in soil of intercropping systems was improved to increase soybean nodule numbers, and lead to increase leaf dry weight, leaf number, plant height, root length and root shoot ratio in intercroppings of mulberry/soybean compared to monoculture. It concluded that mulberry/soybean intercropping has obvious interspecific facilitation.2. It was found that available phosphorus contents in soil, leaf phosphorus and chlorophyll contents in the leaves were increasedin mulberry/soybean and mulberry millet intercropping systems.Net photosynthetic rate and light energy utilization rate in the leaves of mulberry, soybean and millit in intercroppings increased to reduce midday depression of photosynthesis at noon. Land equivalent ratio (LER) and land utilization rate increased in mulberry/millet intercropping system. The mulberry aggressivity in mulberry/millet intercropping was more than that of millet, intercropping reduces LER in mulberry/soybean intercropping. The soybean aggressivity in mulberry/soybean intercropping was more than that of mulberry.Two kinds of intercropping patterns were compared to find that mulberry/millet and mulberry/soybean intercropping not only has the obvious interspecific competition effect, but also interspecific facilitation, and two kinds of interactions co-exist. The results in this paper indicated that scientific hypothesis proposed is correct, which intercroppings between nonleguminous plants not only has the function of interspecific competition, but also has interspecific facilitation.