长期施肥对砂姜黑土大孔隙形态和数量特征的影响

Effects of long-term fertilization on the morphology and quantity of macropores in vertisol

为探明长期施肥对砂姜黑土大孔隙结构的影响,本研究选取37 a田间定位试验的5个处理:不施肥(CK)、单施化肥(NPK)、单施有机肥(M)、等氮条件下有机肥与化肥配施(MNPK)和高氮条件下有机肥与化肥配施(HMNPK),通过X射线CT扫描原状土柱(直径7.4 cm,高20 cm),利用图像处理技术进行土壤孔隙三维结构重建。结果表明,各处理下土壤团聚体结构内部以及团聚体之间均存在大孔隙,尤以M处理数量最多;分形维数和各向异性由大到小次序分别为HMNPK>M>MNPK>NPK>CK和MNPK>CK>M>NPK>HMNPK。与CK相比,有机肥配施处理(M、MNPK、HMNPK)的大孔隙度分别增加7、6、10个百分点,大孔隙数量分别增加41.5%、33.3%、26.8%。HMNPK处理孔径分布呈剧烈的双峰曲线波动,第一和第二峰值分别出现在395~577μm和1545~1701μm处。主成分分析表明,<126μm孔径主要受粉粒含量影响,126~500μm孔径受容重影响,500~2500μm孔径则受砂粒含量、黏粒含量、连通性和分形维数等多因素综合影响。研究表明,有机肥和无机肥长期配施,可显著改善砂姜黑土大孔隙数量和形态特征,尤以HMNPK处理效果最佳,而NPK处理效果不明显。分形维数和连通性可作为砂姜黑土结构改良的定量评价指标。

The effects of long-term fertilization on the macropore microstructure of vertisol were studied.In this study,soil pore structure was assessed using intact soil columns(7.4 cm diameter,20 cm height),which were sampled from five long term fertilization treatments established in 1981,including no fertilizer(CK),inorganic fertilizer(NPK),a single application of organic fertilizer(M),a combination of inorganic fertilizer and organic manure with isonitrogen(MNPK),and a combination of inorganic fertilizer and organic manure with high nitrogen levels(HMNPK).Each column was scanned with X-ray microtomography(μCT)and quantified using image analysis.The results showed that there were macropores in the soil aggregate structure and between the aggregates in each treatment,in particular,the M treatment had the largest number of pores.The order of fractal dimension and anisotropy from large to small was HMNPK>M>MNPK>NPK>CK and MNPK>CK>M>NPK>HMNPK,respectively.Compared with CK,the organic manure treatments(M,MNPK,and HMNPK)increased the number of macropores by 41.5%,33.3%,and 26.8%,while the porosity increased by seven,six,and ten percentage points,respectively.The fluctuations in the pore size distribution of HMNPK treatment were the most intense,with the first and second peaks appearing at 395~577μm and 1545~1701μm,respectively.Principal component analysis showed that pores<126μm in size were mainly affected by particle content,126~500μm pores were affected by bulk density,and 500~2500μm pores were affected by multiple factors,including sand content,clay content,connectivity,and fractal dimension.Overall,this study demonstrates that long-term application of organic and inorganic fertilizers can significantly improve the morphology and quantity of macropores in vertisol,especially HMNPK treatment,while NPK alone caused no significant improvement.Fractal dimension and connectivity could be used as a quantitative evaluation index for improving the pore structure of vertisol.