Quantitative Analysis Of Different Forms Of Nitrogen Fertilizer On Soil Acidification Rate In Pineapple Orchard And Optimization Of Fertilization Measures

Soil acidification as a manifestation of soil degradation.Among them,excessive and long-term input of nitrogen fertilizer is an important cause of soil acidification.Hainan,as the second largest pineapple producing area in China,in recent years,with the long-term succession of pineapples and excessive application of nitrogen fertilizer led to a series of succession of pineapple yield and quality decline,soil acidification and a series of obstacles to the development of the pineapple industry and economic efficiency is seriously restricted.In this study,we quantified the relationship between H⁺production and the actual rate of soil acidification through soil column simulated leaching tests for different types of acidified soils（basaltic brick red soil,dry red soil,granite brick red soil）and different forms of N fertilizer（ammonium N fertilizer,amide N fertilizer）in pineapple plantations in Hainan Province.In response to the results of this study,different fertilization patterns（no fertilization treatment CK;farmer’s conventional fertilization treatment FC;optimized fertilization treatment YH;optimized fertilization+soil improver 1 YHO1;optimized fertilization+soil improver 2 YHO2;optimized fertilization+bio-organic fertilizer YHO3;optimized fertilization+magnesium fertilizer YHO4）were set up through field trials to analyze pineapple orchard soil physicochemical properties,pineapple nutrient utilization and quality and yield effects.To clarify the improvement effect of different fertilization patterns on soil acidification in pineapple orchards,to elucidate feasible measures to alleviate soil acidification in pineapple orchards,and to provide a theoretical basis for the sustainable development of pineapple industry.（1）The soil column simulated leaching test showed that the H+production of pineapple orchard soil showed a 1:1 linear relationship with the leaching of soil salt-based ions,which verified that the actual rate of soil acidification could be quantified by calculating the H+production of pineapple orchard soil.H⁺production of different treatments:ammonium chloride treatment>urea treatment>no fertilizer treatment;salt-based ions(Ca²⁺,Mg²⁺,K⁺,Na⁺)leaching:ammonium chloride treatment>urea treatment>no fertilizer treatment.It indicates that ammonium N fertilizer is more likely to cause soil acidification in pineapple orchards than amide N fertilizer.In addition,the acidification rates of the three soils were different,and the H⁺production and salt-based ion leaching of the three soils were:granite brick red soil>dry red soil>basalt brick red soil.（2）The results of field trials showed that optimized fertilization measures could alleviate the rate of soil acidification and improve soil fertility,with the best effect being the optimized fertilization plus organic fertilizer treatment（YHO3）.Optimization of fertilization practices（YH,YHO1,YHO2,YHO3 and YHO4）can significantly increase soil p H and organic matter content.At fruit harvest,compared with FC treatment,the p H of YH,YHO1,YHO2,YHO3 and YHO4 treatments significantly increased by 7.05%to 24.47%,with YHO3 treatment raising the highest and YHO2 treatment the second highest;at fruit harvest,compared with FC treatment,the soil organic matter content of other optimized fertilization treatments increased by 68%to 104%,with YHO3 treatment had the highest content of0.51%.（3）Compared to FC treatment,optimized fertilization treatments（YH,YHO1,YHO2,YHO3 and YHO4）significantly increased the salt-based ion(Ca²⁺,Mg²⁺,K⁺,Na⁺)content,the amount of exchangeable cations and acid buffer capacity,and decreased the exchangeable acid content in the soil.At fruit harvest,compared to the FC treatment,the optimized fertilization treatment increased the exchangeable calcium content by 6.01%to26.9%,with the highest content in the YHO3 treatment(401.52 mg·kg^﹣1);the exchangeable magnesium by 4.44%to 40.88%,with the highest content in the YHO4 treatment(55.83mg·kg^﹣1);the exchangeable potassium increased by 68.28%～117.05%with the highest content in YHO1 treatment(334.99 mg·kg^﹣1);the exchangeable sodium increased by53.6%～71.37%,with the highest content in YH treatment(334.99 mg·kg^﹣1);cation exchange increased by 45.19%～102.54%,with the highest content in YHO3 treatment(14.34 cmol·kg^﹣1);the exchangeable hydrogen decreased by 60.51%～90.77%,with the lowest content in YHO3 treatment(1.83 mg·kg^﹣1);the exchangeable aluminum decreased by 10.14%to 35.51%,with the lowest content in YHO3 treatment(270.76 mg·kg^﹣1);soil acid buffer capacity of 10-20 mmol·kg^-1 in CK,FC,YH,and YHO4 treatments,and sensitive to acid and susceptible to acid damage,and 20-40 mmol·kg^-1 for YHO1,YHO2,and YHO3treatments,with the highest acid buffer capacity of 32.16 mmol·kg^-1 for YHO3 treatment,followed by YHO2 treatment at 29.42 mmol·kg^-1,slightly sensitive to acid and slightly susceptible to acid damage.The correlation analysis among soil nutrients showed that p H and exchangeable hydrogen and exchangeable aluminum were highly significantly negatively correlated（p<0.001）,and organic matter,exchangeable calcium,exchangeable potassium,exchangeable sodium,cation exchange capacity,and acid buffer capacity were highly significantly positively correlated（p<0.001）,which showed that optimized fertilization measures could alleviate soil acidification in pineapple orchards compared to conventional fertilization treatments.Among them,YHO3 treatment was the most effective.（4）Field trials also demonstrated that optimized fertilization significantly improved the total dry matter quality and intrinsic quality of pineapple.At fruit harvest,FC,YH,YHO1,YHO2,YHO3,and YHO4 treatments increased the total dry matter quality of pineapple by32.5%to 80.86%compared to the control CK treatment,with treatment YHO3 having the best effect.Compared to CK treatment,FC,YH,YHO1,YHO2,YHO3,and YHO4treatments increased fruit sugar content by 10.62%to 123.26%,with treatment YHO4having the best effect.Compared with CK treatment,FC,YH,YHO1,YHO2,YHO3 and YHO4 treatments increased the VC content of fruits by 77.78%～194.45%,with the best effect being treatment YHO4.（5）Optimized fertilization treatments had a significant effect on pineapple yield,compared to conventional treatment FC,YH,YHO1,YHO2,YHO3 and YHO4 treatments increased pineapple yield by 36.46%to 76.71%,with YHO3 treatment having the highest yield of 62.52 t·hm^﹣2.Correlations between yield and soil nutrients and pineapple quality showed that yield was significantly and positively correlated with fast-acting potassium,exchangeable magnesium,exchangeable sodium,and titratable acid,and highly significantly and positively correlated with exchangeable potassium,vitamin C,and sugar content.In summary,excessive application of both ammonium and amide nitrogen fertilizers can lead to large losses of salt-based ions from the soil and accelerate soil acidification in pineapple orchards,so mitigating soil acidification in pineapple orchards by controlling the amount of nitrogen fertilizer applied is an important improvement measure.The results of field trials showed that applying alkaline fertilizers such as soil conditioner on the basis of optimized fertilization with reduced nitrogen and replacing inorganic nitrogen with 20%organic nitrogen can significantly improve soil p H,increase soil salt-based ion content(Ca²⁺,Mg²⁺,K⁺,Na⁺)and alleviate soil acidification in pineapple orchards.It also improves the quality and yield of pineapples.