| Traditional slash-and-burn land preparation methods have strongly affected soil quality and stand productivity of high-intensity Eucalyptus plantations in southern China,and residues retention can return a large amount of biomass and nutrients to the soil.However,the effects of different residue management measures on the decomposition of eucalyptus residues are rarely studied.To explore the effect of different management measures on eucalyptus residue decomposition,soil fertility and stand growth,and the relationship between nutrient release and soil fertility,in no-burning Eucalyptus plantations in Guangxi Hezhou State-owned Daguishan Forest Farm,we were to 5-years-old residues(divided into leaves,twigs,and branches)as the research object,studied the decomposition process,mass residual rate and nutrient dynamic change of residues in different management measures(remove,tile and stacks),and measured 34 indexes including soil physical and chemical properties,microbial biomass,enzyme activity and forest growth.The main results are as follows:(1)The overground biomass of 5-years-old eucalyptus plantation before harvesting was 91.18t/hm2.The biomass of harvest residues was 12.9t/hm2,among which the biomass of branches and leaves were 9.96t/hm2 and 2.94t/hm2,respectively.Residues nutrient stocks(C,N,P,K,Ca,Mg,S,Fe,Mn,Cu,Zn,B)were 7.23t/hm2,which the nutrient stocks of branches and leaves 5.48t/hm2 and 1.75t/hm2,respectively.(2)The contents of initial C,N,P,K and C/N,C/P,C/K,N/P,N/K,P/K ratios were significantly different among the residues(p<0.001).The content of C,N,P and K from high to low was leaves>twigs>branches.The initial C/N and C/P ratios were branches>twigs>leaves from high to low.The initial C/K and P/K ratios were branches>leaves>twigs.The initial N/P ratio from high to low was leaves(16.29)>twigs(8.50)>branches(7.38).The initial N/K ratio of the leaves(1.98)was significantly higher than that of branches and twigs(p<0.001),while the initial N/K ratio of branches(0.98)and twigs(0.97)was not significantly different.(3)After 12 months of decomposition,the mass residual rate from high to low was branches(76.43%)>twigs(64.85%)>leaves(44.01%).Leaves were the fastest decomposition,t50%was 0.82-0.89 years,t95%was 3.56?3.84 years.Twigs were the second fastest decomposition,t50%and t95%were 1.41?1.87 years and 6.08?8.10 years,respectively.Branches were the lowest decomposition,t50%and t95%were 2.13?2.74 years and 9.19?11.84 years,respectively.After 12 month of decomposition,the mass residual rates of leaves,twigs and branches in tile treatment were 4.91%,9.79%and 6.67%lower than those in strip treatment,respectively.Compared with the strip stacking of residues,tile treatment can shorten the decomposition 50%time of leaves by 7.87%,twigs by 24.6%and branches by 22.26%,and the decomposition 95%time of leaves by 7.29%,twigs by 24.94%and branches by 22.38%,promoting residues decomposition.(4)The contents of C and N in the residues were enriched and released in the decomposition process.P content enrichment and release crossed,the overall downward trend.K content showed a net release.C/N,C/P,C/K,N/P,N/K and P/K all showed an upward trend,but the upward trend of different residues was different.After 12 months of decomposition;the release amounts of C and N from high to low were leaves>twigs>branches,and the release amounts of P and K were twigs>branches>leaves.Compared with the strip stacking treatment,the C,N,P,K content and residual rate of the residues under the tile treatment are lower,and the release amount is higher.(5)The mass residual rate was positively correlated with the initial C content and C/N ratio of the residues(p<0.05),and negatively correlated with the initial N content(p<0.05).During the residues decomposition,there was a significant positive correlation between the mass residual rate and the nutrient residual rate(p<0.05),especially the highest positive correlation coefficient between the mass residual rate and the C residual rate.The mass residual rate was negatively correlated with the dynamic changes of N,P and K(p<0.05),and positively correlated with the dynamic changes of C,C/N,C/P,N/P,P/K(p<0.05).(6)Soil bulk density,maximum water holding capacity,capillary water holding capacity,minimum water holding capacity,capillary porosity,pH,total nitrogen,total phosphorus,available phosphorus,available potassium,nitrate nitrogen,available iron,available manganese,available boron,microbial biomass carbon and nitrogen,urease and sucrase were significant differences between different residues management measures(p<0.05).Soil bulk density and pH were the highest under removal treatment,and the content of other indexes was the lowest.There were no significant differences in maximum water holding capacity,capillary water holding capacity,minimum water holding capacity,capillary porosity,total nitrogen and total phosphorus between tile and strip stacking treatments.Compared with other treatments,tile treatment has higher available nutrient content.Microbial biomass carbon,microbial biomass nitrogen and sucrase under tile treatment were significantly higher than those under strip stacking treatment(p<0.05),while urease showed no significant difference.(7)The average ground diameter and diameter at breast height of 1-year-old eucalyptus plantation under the tile treatment were 3.63%and 6.44%higher than those under the removal treatment,and 1.49%and 1.80%higher than those under the strip stacking treatment;and the average tree height was 12.16%higher than that under removal treatment and 0.64%lower than that under strip stacking treatment.However,the effects of different residue management measures on the growth of eucalyptus one-year young forest did not reach the significant level.(8)Results of redundancy analysis showed that the chemical indexes that had a strong correlation with nutrients release decomposed by residues were available potassium,pH value,total nitrogen,nitrate nitrogen,total phosphorus,available boron,available zinc,available manganese and available copper.And biological indicators were:microbial biomass carbon,sucrase,microbial biomass nitrogen and urease.Based on the above results,the tile treatment of the residues under eucalyptus forests can accelerate residues decomposition,accelerate the rate of nutrient cycling,improve the soil fertility under the forests,promote the growth of stands,and be more conducive to the sustainable management of eucalyptus plantations. |
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