Decomposition And Nutrient Release Of Mixed Residues In The Soil Of Poplar-crops Agroforestry System

In the agroforestry system, the mixture of the forest litter and crop straw residues is differentin chemical compositions and physical structure from monoculture, and plays a key role inecosystem nutrient cycle. The agroforestry patterns of poplar-peanut and poplar-wheat, which arethe typical agroforestry models in northern Jiangsu province, were chosen to study the impacts ofmixed residues on decomposition rate, nutrient release, the change of soil fauna and soilrespiration. The main results are as follows:(1)The contents of N,P and Ca and their transfer efficiency in poplar leaves were differentin the various plantations (spacing6m×6m and spacing3m×8m); Compare to poplarNanlin-95, the contents of N,P and Ca were lower, and thetransfer efficiency was higher inpoplar Nanlin-895.(2)The decomposition rate displayed in the order of H＞HJ＞Y＞M for singleresidue treatments, while it was ranged as Y-H＞Y-HJ＞Y-M in mixed residue treatments. Atthe end of experiment, the mixture of the forest litter and crop residues demonstratedsignificantly stimulative effects on the decomposition rate.(3)N and P contents in poplar leaf litter and wheat straw residues mainly manifested asenrichment during the initial stage of decomposition, then released gradually. K content in peanutleaf residue was the lowest, but weight loss rate of total K was much higher than other treatments.On the contrary, K content in wheat straw residues was the highest, and weight loss rate of totalK was lower than other treatments during initial stage. In summer (July), Ca in the treatmentsbegan to release. N and P content in the poplar and wheat straw residues mainly manifested asenrichment during the initial stage of decomposition, then released gradually. There was asignificant net release of Mg in poplar leaf litter and peanut litter, while wheat and peanut stalkresidues demostrated enrichment effect for Mg during initial stage. The mixture of the forest litterand crop residues showed a significant stimulative effect on the nutrient release.(4)Acarina and Collembola were the dominant groups of soil fauna in litters. Duringsummer, the decomposition rate was well correlated with the population density of soil fauna, butthis phenomenon was not observed in winter.(5)In Spring and Summer, the soil respiration increased significantly after adding peanutleaf residue and peanut stalk residue. In Autumn, the soil respiration was lower in the treatmentsof adding peanut leaf residue and wheat straw residues into soils.(6)The cumulated carbon mineralization displayed in the order of H＞HJ, Y＞M＞CKfor single residue treatments, while it was ranged as Y-H＞Y-HJ＞Y-M in mixed residuetreatments. At the end of incubation, the mixture of the forest litter and crop straw residues demonstrated significant stimulative effect on the cumulated carbon mineralization. A significantcorrelation was observed among nitrogen contents in litters, carbon-nitrogen ratio and microbialbiomass carbon and nitrogen in the soil. In mixed residue treatments, higher microbial biomasscarbon and nitrogen, and lower carbon-nitrogen ratio in the soil were observed in treatment ofY-H, while lower microbial biomass carbon and nitrogen, and higher carbon-nitrogen ratio weremeasured in treament of Y-M. When poplar leaf litter, wheat straw residue and their mixture wereadded to the soil, the contents of mineral nitrogen was significantly lower than the control.However, when peanut leaf residue, peanut stalk residue, and their mixed residues with thepoplar leaf litter were added, the contents of mineral nitrogen in soil increased significantly.(7)The cumulated carbon mineralization was significantly higher in the treatment ofadding poplar leaf litter intervally than that of adding all at the first day. The microbial biomasscarbon and nitrogen were significantly higher in the treatment of adding poplar leaf litterintervally than that of adding all at the first day. Compared to the CK, the content of soilinorganic nitrogen decreased significantly for all the residue addition treatments, especially in themixed residues treatments.