不同连作年限对菠萝园土壤养分及可培养微生物数量的影响

菠萝(Ananas comosus)是我国最重要的经济作物之一，长期连作会导致严重的连作障碍，严重影响菠萝产业的发展。本研究以海南省琼海市不同连作年限（4、6、8、10、12 a）的菠萝园土壤为研究对象，采用田间采样及室内分析相结合的方法，研究连作菠萝园的土壤养分及可培养微生物数量的变化。结果表明:随着连作年限的增加，土壤酸化逐渐严重，土壤有机质、碱解氮含量呈下降趋势；土壤速效钾含量呈现先下降再升高的趋势；土壤速效磷含量随着连作年限的延长而增加，呈强烈的富集作用；土壤交换性钙、镁含量则在连作8、10 a土壤中积累量最多。土壤可培养细菌、放线菌数量随着连作年限的增加逐渐减少，而土壤可培养真菌数量呈逐渐增加的趋势。冗余分析结果表明，可培养细菌数量与土壤速效磷、pH含量呈正相关；可培养真菌、放线菌数量与土壤碱解氮、有机质、速效钾含量呈正相关。由此可见，菠萝长期连作改变了菠萝园土壤中养分的比例，导致土壤中可培养微生物数量失调，进而影响菠萝的生长。

Effects of Different Continuous Cropping Years on Soil Nutrients and Culturable Microorganisms in Pineapple Orchards

Pineapple is one of the most important cash crops in China. Long-term continuous cropping causes a serious obstruction to continuous cropping and gives a serious impact to the development of pineapple industry in China. The soil samples （from Qiong Hai city of Hainan）in the pineapple orchards for different consecutive cropping years (4, 6, 8, 10, and 12 years) were collected to analyze the changes in soil nutrients and the number of culturable microorganisms in the pineapple orchards. The results show that the soil acidification in the pineapple orchards becomes more and more serious with the continuous cropping years. The contents of organic matter and alkali-hydrolyzed nitrogen in soil decreased. The content of available potassium in the soil decreased firstly and then increased. The content of available phosphorus in the soil increased with the continuous cropping years and showed a high enrichment effect. The soil contents of exchangeable calcium and magnesium were mostly accumulated in the pineapple orchards for 8 and 10 years of continuous cropping. The number of culturable bacteria and actinomycetes in the soil decreased gradually with the increase of continuous cropping years, while the number of culturable fungi in the soil increased gradually. Redundancy analysis showed that the number of culturable bacteria was positively correlated with the content of available phosphorus and pH. The number of culturable fungi and actinomycetes was positively correlated with the contents of alkali-hydrolyzed nitrogen, organic matter and available potassium in the soil. Thus, the long-term continuous cropping of pineapple changes the proportion of soil nutrients in the pineapple orchards, resulting in the imbalance of the number of culturable microorganisms in the soil, thus affecting the growth of pineapple.