‘南丰蜜橘’园生草对土壤团聚体养分和微生物特性及果实品质的影响

Effects of grass cover in‘Nanfeng’tangerine orchard on nutrients and microbial characteristics in soil aggregates and fruit quality

【目的】探明生草对橘园土壤团聚体养分特性和微生物特性的影响,为构建合理的土壤管理模式提供科学依据。【方法】以‘南丰蜜橘’园为研究对象,分析行间播种白三叶草、黑麦草和清耕条件下土壤团聚体养分含量、微生物生物量、微生物功能多样性和活性的差异。【结果】与清耕对照比,生草栽培显著提高了土壤团聚体有机碳、全氮、全磷、全钾、硝态氮、速效磷、速效钾和微生物量碳、氮、磷的含量以及呼吸强度、多样性指数(p<0.05),黑麦草处理团聚体平均增幅分别为112.37%、29.44%、63.00%、80.68%、24.39%、21.96%、111.09%、69.95%、12.73%、26.28%、27.58%、20.35%,白三叶草处理团聚体平均增幅分别为122.57%、55.29%、57.62%、54.97%、44.54%、23.83%、65.17%、94.47%、42.68%、22.06%、28.02%、22.12%。生草能明显提高果实可溶性糖、可溶性固形物和维生素C含量,降低可滴定酸含量。【结论】生草栽培提高了橘园土壤各粒径团聚体的养分含量和微生物量碳、氮、磷含量,增加了橘园土壤团聚体微生物功能多样性和代谢活性,提升了橘园土壤肥力和健康状况,进而改善了‘南丰蜜橘’鲜食品质。

【Objective】‘Nanfeng’tangerine is a well-known citrus variety in China.‘Nanfeng’tangerine is popular in the market and has been widely cultivated in many regions.In 2018,‘Nanfeng’tangerine cultivation area reached 78000 hm^2 with a production of 1.35 million tons.However,due to the long-term traditional orchard cleaning practice,a series of ecological and environmental problems such as reduced soil quality,reduced fertility,increased pests and diseases,and soil erosion have resulted in serious impacts on‘Nanfeng’tangerine productivity,quality,and thus profit.Grass cover is an advanced orchard management,which can significantly increase soil organic matter and nutrients,improve orchard soil quality,repair orchard ecological environment,improve fruit yield and quality,effectively solve problems caused by long-term cleaning of orchards.This experiment used traditional orchard cultivation methods(clean cultivation)as the control to examine the effects of grass cover treatments on nutrient and microbial characteristics of the soil aggregates in‘Nanfeng’tangerine orchard.【Methods】Three treatments including ryegrass as the cover grass(T1),white clover as cover grass(T2),and orchard cleaning as the control(CK)were set in the experiment,which was of one-factor randomized block design with 3 biological replicates.In late July 2019,the five-point sampling method was used for sample collecting.0-20 cm soil layer sample was taken 30 to 40 cm away from the trunk of the trees.The contents of soil aggregates of different sizes(<0.25 mm,0.25-0.5 mm,0.5-1 mm,1-2 mm,2-3 mm,3-5 mm and>5 mm)were determined using the thermosieve method.Soil organic carbon content was measured using the method of external thermal oxidation of potassium dichromate under low temperature.Soil total nitrogen content was determined with Kjeldahl method and nitrate nitrogen content with a dual-wavelength ultraviolet spectrophotometry.Total phosphorus and available phosphorus contents were measured with the molybdenum antimony colorimetry,and total potassium and available potassium contents with the flame photometric method.Soil microbial biomass carbon,nitrogen,and phosphorus contents were determined by chloroform fumigation extraction method.Soil basal respiration intensity was measured indoor with closed culture method.Functional diversity of soil microbial communities was measured with the BIOLOG ecological test board.【Results】Soil R0.25 in various treatments followed a pattern of T1>T2>CK.Grass cover treatments were favorable for the formation of large soil aggregates.Compared with CK,grass cultivation increased soil organic carbon,total nitrogen,total phosphorus,total potassium,nitrate nitrogen,available phosphorus,and available potassium.Their average increase was 112.37%,29.44%,63.00%,80.68%,24.39%,21.96%,111.09%,respectively in T1 and 122.57%,55.29%,57.62%,54.97%,44.54%,23.83%and 65.17%respectively,in T2.The contents of microbial biomass carbon,nitrogen and phosphorus increased significantly in soil aggregates(p<0.05),and their average increase was 69.95%,12.73%and 26.28%respectively in T1 and 94.47%,42.68%,and 22.06%respectively in T2.The respiration intensity of soil aggregates was enhanced remarkably(p<0.05)and the average increase was 27.58%and 28.02%in T1 and T2,respectively.Species richness index,dominance index,and evenness index of microbial communities increased in the soil aggregates under grass cultivation.The contents of soil carbon,nitrogen and microbial biomass carbon and nitrogen in T2 were significantly higher than in T1(p<0.05),while the contents of phosphorus and potassium in soil aggregates displayed an opposite pattern.The contents of organic carbon,nitrate nitrogen,available phosphorus,microbial biomass carbon and nitrogen in 3-5 mm aggregates were significantly higher than those in the other sized agglomerates under different treatments.The basal respiration intensity of 3-5 mm,2-3 mm and 1-2 mm aggregates under grass cultivation was significantly higher than that of the other sized aggregates.Naturally grown grass increased soluble sugars,soluble solids and vitamin C and reduce titratable acid.【Conclusion】Planting white clover had a better effect in increasing carbon and nitrogen in soil aggregates but was less effective in increasing phosphorus and potassium than planting ryegrass.Grass cover had a prominent effect in increasing the carbon,nitrogen,and phosphorus in soil aggregates(3-5 mm)and in improving the microbial activity of aggregates(>1 mm).Grass cultivation promoted the formation of large aggregates in the soil in Nanfeng tangerine orchard.It could effectively increase the nutrient content and microbial biomass in soil aggregates of various sizes,enhance the carbon fixation of aggregates and microbial diversity and activity,and thereby improve soil fertility and fruit quality of‘Nanfeng’tangerine.