Seasonal soil and plant nutrients under Ulmus pumila and Robinia pseudocacia mixed plantation

The seasonal soil pH and nutrients and plant N and P uptakes under the monocultures and mixed plantation of Ulmus pumila and Robinia pseudocacia were studied by three root partition methods(partitioning their roots by nylon net,no partitioning their roots and partitioning their roots by plastic film)and two fertilization methods(fertilizing them and not fertilizing them) The results showed that the soil pH increased from May to September in the monoculture and mixed plantation of Ulmus pumila and Robinia pseudocacia.The soil pH decreased significantly in the mixed plantation of Ulmus pumila and Robinia pseudocacia than that of their monocultures,and this particularly appeared more evident where their roots were not partitioned or roots partitioned by nylon net.The soil organic matter contents were higher in July under the monocultures and mixed plantation and higher where fertilization was done than where fertilization was not done,and ranked in the order of not partitioning the roots partitioning the roots by nylon net partitioning the roots by plastic film.The soil Nitrate-N contents under the monocultures and mixed plantation of Ulmus pumil and Robinia pseudocacia tended to decrease as the seasons changed.In the whole growth periods of Ulmus pumil and Robinia pseudocacia,the soil Ammonium-N made up a great majority of soil N nutrients and the soil Nitrate-N did an extreme small part of them,which showed that the main form by which Ulmus pumil and Robinia pseudocacia absorbed N was NH4+-N.The total N and P uptakes of Ulmus pumil and Robinia pseudocacia tended to increase from May to September and peaked in September.The total N and P uptakes of Ulmus pumil and Robinia pseudocacia in their mixed plantation were higher than those in their monocultures,but the total N and P uptakes of Ulmus pumil and Robinia pseudocacia under their monoculture and mixed plantation differently varied.The best soil improvement as well as the optimum N and P total uptakes of Ulmus pumila and Robinia pseudoacacia appeared where their roots were not partitioned and they were fertilized.