Effects Of Mulching Combined With Nitrogen Fertilizer On C:N:P Stoichiometry Of Soil-fruit Tree System On The Loess Plateau

The Loess Plateau is a world-recognized high-quality apple producing area and its apple yield and cultivation area rank first in the world.The apple industry has become a superior industry to improve the ecological environment and promote regional economic development.Orchard management measures such as mulching and fertilization are widely applied in practically to improve orchard productivity and the soil fertility,which not only greatly affected soil carbon(C),nitrogen(N),phosphorus(P)and potassium(K)content,also alter in the stoichiometric ratio of C,N,P and K in soil and fruit trees.Present study explored the alteration of C,N,P,K nutrient contents in soil-tree system under different horticultural mulching combined with distinct nitrogen addition treatments,and discussed the different mulching management and N addition on the stoichiometric characteristics of orchard ecosystems in the Loess Plateau.Additionally,studied the interaction and balance constraints among elements,aimed to provide a theoretical basis for the optimization of soil management technology in apple orchards in this area.The main results of this study are as follows:(1)Mulching and fertilization measures had varying degrees of impact on apple yield and quality: Appropriate addition of nitrogen fertilizer under mulching approaches was conducive to increase apple yield and quality improvement.The apple yield under different mulching treatment was: Cover straw(CS)> Black ground fabric(BF)> Perennial ryegrass(RE)> Clean tillage(CT),notably the straw mulching significantly improved the single fruit weight.Appropriate addition of nitrogen fertilizer(0.25 N and 0.5N)significantly increased the yield,fruit weight,soluble solids,soluble sugar and Vitamin C(VC)contents.While the sugar-acid ratio and soluble solids content of fruit were significantly reduced when highly applied N fertilizer(0.75N).Therefore,from the perspective of fruit quality and yield,the orchard management measures are recommended to apply straw mulching first,followed by ground distribution and grass mulching,and the reasonable amount of nitrogen fertilizer is between 0.25 N and 0.5N.(2)Revealed the effects of distinct mulching measures on the nutrient and stoichiometric characteristics of the soil-fruit tree system.Under different mulching measures,the order of nitrogen and phosphorus content from high to low was CS > RE >BF > CT,and there was no significant change in soil potassium content,CS and RE mulching were favorable to soil nutrient accumulation in the orchard.The contents of C,N,P and K in leaves of fruit trees were increased under all mulching treatments,among which,the carbon content of leaves was significantly increased by RE treatment,while the nitrogen content of leaves was significantly increased by BF and CS treatments.The RE treatments significantly increased fruit carbon content,while all mulching treatments decreased fruit N and P content,but no significant effect on K.The highest effect of C : N and C : P in 0-40 cm soil layer was present in CS,and there was no significant difference in soil N : P among all treatments.Moreover,there was no significant difference in leaf C : P and C : P among various mulching treatments,but CS and RE significantly decreased leaf N : P and N : K,respectively.Mulching treatment increased fruit C : N and C : P,but decreased fruit N : K.(3)Investigated the effects of different nitrogen additions on the nutrient and stoichiometric characteristics of the soil-fruit tree system.The content of soil total nitrogen(STN)increased with the increase of N addition,and soil total phosphorus(STP)and soil total potassium(STK)contents were decreased to varying degrees,especially under the intercropping RE management mode.N addition significantly increased the leaf C,N contents and fruit C,N,P and K contents.Under different amount of nitrogen addition,soil C : N,C : P and N : P ranged from 11.87～41.63,8.17～45.00 and 0.35～1.71,respectively.Nitrogen addition significantly reduced soil C : N,and increased soil C : P that was positively related with nitrogen addition.Furthermore,nitrogen addition increased the N : P of leaves while varying degrees reduced the C : N and C : P ratios of fruits.Nitrogen application affected the growth of fruit trees by changing the content of C,N and the ratio of C,N and P in leaves and fruits,and significantly affected the content of K in fruits.