Experimental Study On Characteristics Of Phosphorus Competition In Hedgerow-Intercropping System

Agroforestry is a reasonable land use for development of mountain and hill regions and soil erosion control. Set Vetiveria zizanioides and Amorpha fruticosa as hedgerows and intercropping with wheat-soybean to make the system, crops biomass and yield, phosphorus concentration, uptake of hedgerows and crops were measured. Without phosphorus fertilization pot and field experiments were conducted to study phosphorus competitive absorbability of hedgerows and crops with using the equation on competitive intensity, the results are as follows:The biomass and grain yield of wheat are higher in intercropping than in monoculture, while the biomass and grain yield of soybean are lower. The system of wheat intercropping with hedgerow has possessing intercropping advantage, and as the dominant species wheat is more competent than hedgerow, while that of soybean / hedgerow is not advantageous. Using the competitive intensity equation of Perera the interaction between crops and hedgerows is studied. The competitive intensity of wheat/ Amorpha fruticosa and wheat/ Vetiveria zizanioides are respectively 0.26 and 0.14, and that in field experiment are 0.086 and 0.0086, which shows the interaction between wheat and hedgerows is less stronger than that between crops. The competitive intensity of soybean/ Amorpha fruticosa and soybean/ Vetiveria zizanioides is respectively -0.34 and -0.39, which demonstrates the interaction between soybean and hedgerows is stronger.The distance between crops and hedgerows affects the biomass and grain yield of crops. Hedgerows improve neighbor wheat, and Vetiveria zizanioides affect stronger than Amorpha fruticosa, but the accelerating effect decrease with increasing distance and disappear at the third row. At the same time, hedgerows have competent effect on neighbor soybean, and it disappear at the forth row. However the biomass and grain yield of soybean increase with increasing distance intercropping with Amorpha fruticosa, and increase at the second and forth row intercropping with Vetiveria zizanioides.The aboveground and belowground competitive intensity are respectively studied using different root separations. So, total competitive intensity could be composed of aboveground and belowground competitive. The ACI of wheat/hedgerow is more than zero, which shows the aboveground effect on wheat by hedgerows is less than that on wheat-by-wheat, and the aboveground effect is stronger than belowground. While the aboveground effect of soybean/ Amorpha fruticosa is stronger than belowground, the belowground effect of soybean/ Vetiveria zizanioides is stronger than aboveground.The P concentration of wheat intercropping with hedgerows is different in potexperiment and field experiment. The P concentration of intercropping wheat is lower than that of monoculture wheat in pot experiment, but higher than that of monoculture wheat in field experiment. Comparing the difference of the experimental condition we can think the reason is the increasing area of P acquisition. Because in pot experiment root is limited in small area, P concentration is low, which is typical for the wheat/ Vetiveria zizanioides with no barriers, P is so sensitive that P concentration of wheat great increases when the belowground root effect of different species is removed (with solid barrier). In field, wheat and hedgerows have advantageous to absorb P, and then competition is eliminated. The P concentration of soybean when intercropping with hedgerows decreased in pot experiment, while it changes with the distance between soybean and hedgerows in field experiment. In all, the P concentration of crops decrease because of limited area for crops and hedgerows to grow in pot experiment, and increase because of enlarged area in field experiment.The P acquisition of agroforestry is affected not only by the different P utilization ability of plant, but also by the interaction between different species. In field experiment the P acquisition of wheat / Amorpha fruticosa per area is 31.6% higher than sole cropping system, and that of wheat / Vetiveria zizanioides is 41.5% higher than sole cropping system, which proves the interaction obviously accelerates P acquisition; the soybean / hedgerows as well. In pot experiment except that the P acquisition of wheat / Vetiveria zizanioides and soybean / Vetiveria zizanioides is respectively 1.8% and 8.9% higher than sole cropping system; the P acquisition of other treatment is lower. The P acquisition of agroforestry system decreases, which show that the competition for P happens between crop and hedgerows, the competition method is that crop and hedgerow compete to absorb P through their roots intercrossing. It is propitious to P acquisition of the system when the belowground root effect is removed (with solid barrier).The competition method also can be embodied through the biomass of intercropping hedgerows change. The biomass of hedgerows intercropping with whatever crops in this study is lower than that of monoculture hedgerows in pot experiment, while higher in field experiment. Comparing the difference of their growing condition, we can presume enlarged belowground area result in the biomass increasing of intercropping hedgerows.