Soil PH Suitable For Litchi Growth And Application Comparison Of Different Soil PH Improvers In Litchi

Litchi is a tropical and subtropical fruit with the largest plantation area in South China,and litchi production becomes the mainstay of the rural economy in this region.Soil p H is commonly low in litchi orchard of southern China,however,alkalescent in some litchi orchards in Luzhou Sichuan,southwest China.It is recognized that soil p H greatly affect the physical and chemical properties of soil and plant growth.In the present study,a typical latosolic red soil with the p H of 4.2±0.2 and from South China was used to conduct a soil incubation and a litchi culture experiment.The trial included six treatments with various soil p H,which were adjusted by addition of 0.5 g?kg^-1 sulfur and 0.5,1,2 and4 g?kg^-1 of line,respectively.Effect of soil p H on soil fertility,enzyme activity and plant growth of litchi was examined,with the objectives to identify the suitable soil p H for litchi growth.Meanwhile,an acidic litchi orchard soil?latosolic red soil,p H 4.2±0.2?and an alkalescent litchi orchard?calcium soil,p H 7.5±0.1?were collected to carry out soil incubations and litchi culture experiments.Lime(1 g?kg^-1),dolomite(2 g?kg^-1)and calcium magnesium phosphate(Ca Mg P,0.625 and 4 g?kg^-1)were spiked in the latosolic red soil,and sulfur(2 g?kg^-1),aluminum sulfate(4 g?kg^-1)and pyrite(4 g?kg^-1)were applied in the calcium soil to investigate the influence of different amendments on soil p H and litchi growth.The results are shown as below:?1?Sulphur application increased both active and latent acidity in latosolic red soil,whereas lime addition rapidly decreased both active and latent acidity in calcium soil.Soil p H extracted by water and KCl increased with increasing lime rate,and significantly enhanced by lime application at the rates of 2 and 4 g?kg^-1?p<0.05?.Meanwhile,soil available P,Ca,Mg,Cu and Zn were increased,but soil acid phosphatase activity?PPA?was inhibited and soil urease activity?UA?was not affected by sulfur amendment.Soil available N,K,Zn,UA and PPA were reduced by lime application,and the decrements of all the attributes except available Zn increased with increasing lime dose.Simultaneously,lime utilization increased soil available P,Ca and Cu,while soil available Mn was decreased by low level of lime and increased by high level of lime.Soil available N,K,Mg,UA and PPA were significantly and negatively correlated to soil p H?extracted with water?within the p H range of 3.84±0.10⁸.03±0.15 in this incubation,with the Pearson coefficients of-0.529**,-0.850**,-0.579**,-0.458** and-0.872**,respectively.However,significant and positive correlations were observed between soil available P,Ca,Cu and soil p H with the Pearson coefficients of 0.380**,0.914** and 0.375**,respectively.Additionally,application of sulfur and lime rapidly improved the crystallization of kaolinite in latosolic red acid,however,this effect diminished asthe incubation time went on.?2?Addition of lime,dolomite and Ca Mg P sharply decreased the active and the latent acidity of soils.Application of 2 g?kg^-1 dolomite and 4 g?kg^-1 Ca Mg P significantly increased soil p H extracted by water and KCl at the end of the incubation.Soil available N and K were reduced by dolomite and Ca Mg P amendments.Soil available P,Ca,Mg,Cu,Fe and Mn were increased by application of the three amendments,and the increments increased with increasing Ca Mg P rate.Addition of dolomite suppressed soil UA and PPA,while Ca Mg P amendment enhanced soil UA but inhibited PPA.The mineral composition in latosolic red soil was not affected by application of both dolomite and Ca Mg P,however,the crystallization of kaolinite was improved,which was beneficial for water and soil conservation.?3?Soil p H extracted by water and KCl were slightly decreased by addition of sulfur,aluminum sulfate and troilite in calcium soil.Sulfur application increased soil available P,Ca,Mg,Cu,Fe and Mn,troilite increased soil available P,Mg,Cu,Fe and Zn,and aluminum sulfate enhanced soil available P but decreased soil available Zn.Soil UA was promoted by sulfur addition,and soil alkaline phosphatase activity was suppressed by application of the three amendments.?4?In contrast to the control,sulfur addition reduced the net photosynthesis rate and chlorophyll indices of litchi seedlings in latosolic red soil,decreased the leaf number and stem girth,leading to inhibited plant growth.The growth of litchi seedlings was suppressed by application of 0.5,2 and 4 g?kg^-1 lime as well.However,lime addition at the rate of 1g?kg^-1 lime promoted the net photosynthesis rate,transpiration rate and chlorophyll indices of litchi seedlings,and enhanced the leaf number and stem girth,resulting in better plant growth.The above indicates that soil p H in extremely low or high level impacts litchi growth.?5?Litchi growth was enhanced by application of dolomite and CaMgP in latosolic red soil,with higher net photosynthesis rate,transpiration rate and chlorophyll indices,more leaves and bigger stem girth.High rate of Ca Mg P and dolomite were superior to lime and low rate of Ca Mg P in growth promotion in litchi.?6?Addition of sulfur,aluminum and troilite slightly increased the photosynthesis of litchi seedlings,however,did not greatly improve litchi growth.Growth promotion in litchi by sulfur application was relatively more obvious than that by addition of aluminum and troilite.Conclusively,litchi growth became worse when soil p H was lower than 4.50 in latosolic red soil.When soil p H was increased to 5.09±0.59 by lime application,soil fertility and enzyme activity varied moderately,and litchi growth was greatly improved.While soil p H was further increased to higher than 6.07,litchi seedlings grew worse.It shows that when lime is used in acid soil,the suitable soil p H ranges from 5.09±0.59.When dolomite and high rate of Ca Mg P was applied in acid soil,soil p H significantly increased to 5.28±0.18⁶.63±0.07,and litchi growth was further improved as compared to lime.Consequently,dolomite and proper rate of Ca Mg P are suitable soil p H amendments for latosolic red acid.In calcium soil,even a large amount of soil amendment was applied,litchi growth was not greatly enhanced.Hence,litchi is not recommended to be cultivated in this soil.