Effects Of Mulching On Pitaya Soil Environment Andplant Growth In Hainan Province

Hainan province,located in the southernmost part of China and in the north edge of the tropics,with advantaged rain and heat resources,was the most suitable areas for pitaya growth,and expanding cultivated area to over 70000 acres in Hainan province by the year 2000.These issues included soil structure breakdown,and soil fertility degradation,which were caused by relatively backward state of the land management,affected the fruit yield and quality.But the effects of mulching methods on the pitaya soil and tree growth are controversial and not well understood.To address this,we investigated the physical and chemical characteristics and microbial characters of soil in four representative pitaya orchards which were covered in different ways.Next,we studied the comparison of five mulching treatments to make clear the effects of different mulching pattern on the soil chemicophysical properties,soil enzyme activities,soil microbial biomass C and N,soil microbial community structure,the growing state of root and stems and fruit yield and quality.The five mulching treatments were:controlling weeds by herbicides,black fabric cloth mulching,coco coir mulching,nature grass mulching and herba portulacae mulching.The content of this research is as follows:(1)An investigation of chemical characteristics properties and enzyme activities of soil was carried out including 4 pitaya orchards(Nanding orchard with natural grass and black fabric cloth mulch;Beiwei orchard with herba portulacae mulch;Fulin orchard with living mulch;Liguo orchard with black fabric cloth and controlling weeds by herbicides)distributed in main product area in Hainan province.The content of organic matter and total nitrogenwere 19.00 g/kg and 1.13g/kg respectively,which were higher in Nanding orchard with living mulching than in the other orchards and the black fabric cloth area in the same orchard(P<0.05).The soil enzyme activities is much the same,the soil catalase,soil acid phosphatase and soil sucrase had the highest activities in Nanding orchard with living mulching(P<0.05),which were 5.21 U/g?0.42U/g and 21.90U/g respectively.These results showed that,long term nature grass mulching in pitaya orchards was beneficial to accumulate soil nutrition and increase soil enzyme activity.The soil bulk density and soil pH were higher in Nanding orchard,which might be due to the soil conditions.The content of organic matter,total nitrogen,available nitrogen,total phosphorus,available phosphorus and soil enzyme activities in Liguo orchard were more higher in black fabric cloth mulching area than in controlling weeds area(P<0.05).The results showed that black fabric cloth mulching can reduce soil nutrients loss and increase soil enzyme activity.The soil nutrients and soil enzyme activity were poorer in Fulin orchard and Beiwei orchard.(2)Abundance and diversity of soil bacteria and fungi were compared in 2 pitaya orchards where the soil type and management procedures are congruent.The results showed that,the abundance and diversity of bacteria in Fulin orchard were higher than in Liguo orchard,the copy number of soil bacteria in Fulin orchard was approximately twice as large compared to Liguo orchard.And for fungi the results were opposite,the number of soil fungi in Liguo orchard was 3.69 times higher than in Fulin orchard.(3)The field experimental results showed that the contents of soil organic matter and N,P,K were obviously increased in different mulching treatments compared to the controlling weed group,the nature grass mulching gave a good result,followed by coco coir mulching.The content of organic matter and available nitrogen in topsoil were 20.62g/kg and 51.07 mg/kg respectively.Soil enzyme activities were highest in nature grass mulching,followed by coco coir mulching and herba portulacae mulching.The results showed that sown grass and organism mulching were helpful for improving soil nutrient and soil enzyme;Coco coir mulching which was useful for reducing soil erosion and replenishing soil nutrients worked better than black fabric cloth mulching;The fertilizing effect was better in nature grass mulching than herba portulacae mulching.(4)The contents of soil microorganism carbon and nitrogen and the diversity of the bacteria and fungi community structure were higher in any mulching treatments compared to the controlling weed group.The contents of microbial biomass carbon and nitrogen were highest in nature grass mulching(P<0.05),which were 993.33 mg/kg and 41.54mg/kg respectively.The copy number of soil bacteria in nature grass mulching and herba portulacae mulching were 1.82×106 ? 1.59×106 respectively,which higher than other mulching treatments(P<0.05).The results showed that nature grass mulching was useful for improving soil fertility,soil water and thermal conditions,and also helpful to boost soil microbial activities.The contents of microbial biomass and microbial diversity were higher in coco coir mulching and herba portulacae mulching than in black fabric cloth mulching and controlling weed group.(5)For the index of pitaya root morphological,the closer to the topsoil,the difference were more obvious.The indexs of root system(Root total length,root surface area,root diameter,root tip number and fine-root branches)in the topsoil of 0?15cm were highest in nature living mulching,next was coco coir mulching and herba portulacae mulching,and black fabric cloth mulching and controlling weed group were the worst,as well as the physiological character of pitaya stem.These showed that nature grass mulching prompted the growth of roots and shoots.(6)The fruit yield and quality were highest in nature grass mulching of all mulching treatments.The contents of soluble sugar and soluble protein were higher in herba portulacae mulching(P<0.05).The fruits had higher content of vitamin C and soluble sugar in coco coir mulching.The fruits of black fabric cloth mulching and controlling weed group had poor quality and yield.The results demonstrated that,nature grass mulching not only improved soil fertility and soil moisture,but also improved the ecological environment,which was helpful for creating favorable conditions for the vegetative and reproductive growth and quality of fruits,the coco coir mulching excelled obviously black fabric cloth.To sum up,bare ground by controlling weeds,might cause soil structure destroying and soil erosion and also reduce nutrient contents and microbial diversities,affected the growth of fruit tree.Black fabric cloth was useful for preserving soil moisture and nutrients,but this was not quite suitable in Hainan province because of unique climatic condition.Coco coir mulching worked better than black fabric cloth and played a good role to improve soil moisture and nutrient status.Nature grass and organism mulching could obviously increase soil nutrient and moisture and improve the orchard environment,so nature grass mulching was more effective than other treatments.The herba portulacae mulching was less effective than nature grass mulching.