Interspecific Competition For Nutrients And Nitrogen Transfer Between The Intercropped Legume And Cereal

Intercropping, a widely accepted practice in many labor-intensive cultivation countries, with the aim of harvesting at least two crops in one field during a certain period, could be an alternative agronomical measure to counter the contradict between the ever increasing population pressure and the shortage of resources due to its lower risk against unpredictable climate change and unsteady market, and due to its higher efficient resources utilization as well. Legumes and cereals intercropping is one of the most common practices for enhancing grain yield per unit land area and played a crucial role in Chinese traditional agriculture. The yield advantage in these intercropping systems has been well documented during the past decades. However, the effect of interspecific roots interaction on nutrients competition and facilitation was not studied so well. There were some information on economical N use in legumes and cereal intercropping. Nevertheless, the key mechanism supporting the phenomenon was nothing but assumption. Moreover, the work on nitrogen transfer characterized with intercropping practiced in China was not well studied yet. Thus, research on nitrogen facilitation between intercropped legumes and cereal has to be implemented. The aim of our present work was to compare the nutrient competition and facilitation in wheat-soybean and wheat-fababean intercropping systems, and the emphasis was put on nitrogen facilitation and nitrogen transfer in wheat-fababean intercropping. The hypothesis supporting the experiment reported were as the following: the nodule of intercropped legume developed from infection of microbe in the rhizosphere into host roots, which then fixed N2. The fixed nitrogen can be acquired by the companion crop and succeeding crop via direct or indirect nitrogen release in different forms, and N transfer can be determined by injecting 15N into the petiole of fababean, and by measuring 15N abundance in wheat and fababean; Moreover, the symbiotic nitrogen fixation of legume can be enhanced by the nitrogen competition from the associated non-legume.Roots barriers technique was then used to compare the difference in nutrient use between intercropped wheat-fababean and wheat-soybean; Nitrogen isotope dilution method combined with root barriers technique was applied to study the difference between wheat and fababean in the nitrogen source utilization, and the interspecific competition and facilitation for nutrients were analyzed within the root barriers; To estimate the nitrogen transfer, 15N was injected into the petiole of fababean, and !>N can be determined in the associate wheat. The results were as the following:1. Wheat was the dominating crop in aspects of both the growth and nutrients competition either in wheat-fababean or in wheat-soybean system due to its stronger competition, and the growth of soybean but not fababean was suppressed by wheat; the interspecific competition was obvious in wheat-soybean but both the interspecific facilitation of nitrogen and phosphorus was obvious in wheat-fababean.2. The effects of rhizobial strains on the intercropped fababean and wheat differed from strain to strain. All the strains used enhanced the growth of fababean with the solid barrier. Compared with no inoculating, the biomass of fababean inoculated with NM353, LN732 and LN566 was improved by 32%, 13% and 22%, respectively. However, the effects of rhizobial strains varied in nutrient competition as with mesh barrier and without barrier. Rhizobial strain NM353 was the best one in enhancing both the growth of fababean and the associated wheat. The biomass of fababean inoculated with NM353 was the highest, which was increased by 15%, 29% and 15% over that inoculated with LN 732, LN566 and non-inoculants, respectively. In the meanwhile, the biomass of wheat was increased 15%, 22% and 12%. When no barrier was used, nitrate remained in the soil was the lowest among the three root barriers patterns, a promising way for future field study with respect to economic nitrogen use and environ...