河西灌区不同生长年限紫花苜蓿土壤生态化学计量及酶活性响应特征研究

Characterization of carbon,nitrogen and enzyme activity response of alfalfa soils with different growing years in Hexi irrigation area

摘要:

【目的】探究土壤生态化学计量特征和酶活性对紫花苜蓿种植年限的响应。【方法】以河西灌区紫花苜蓿不同生长年限(2、3、4、5、6和7年)及不同土层深度(0~20、20~40、40~60、60~80和80~100 cm)为研究对象,测定土壤理化性质、生态化学计量特征及酶活性,分析种植年限和土层深度对其变化的影响。【结果】1)土壤容重和孔隙度随种植年限增加呈现先升高后降低趋势,5年生紫花苜蓿草地40~60 cm土层的土壤容重较高(1.76 g/cm³),而7年生紫花苜蓿草地60~80 cm土层的土壤孔隙度较高(51.29%);2)随着紫花苜蓿种植年限的增加,土壤有机碳(SOC)含量逐渐升高,而土壤全氮(TN)和全磷(TP)含量均呈现先增高后降低的趋势;土壤C:N在4.81~28.85,除个别年限深层土样外,C:N均高于全国平均水平(13.3),表明土壤氮素相对缺乏。而C:P、N:P分别在1.53~19.54和0.19~1.12,均低于全国平均水平(136和9.30);3)土壤酶活性随年限增加呈先升高后降低趋势,其中,蔗糖酶活性在第3年最高,较2年生紫花苜蓿地提高47.87%;过氧化氢酶和脲酶活性分别在第6年和第5年最高,分别较2年生紫花苜蓿地提高66.67%和17.07%。【结论】紫花苜蓿地在种植到第6年即出现老化现象,因此,种植5年效果最佳,同时要对紫花苜蓿地补施肥料。

Abstract:

【Objective】To reveal the response of soil ecological stoichiometric characteristics and enzyme activities to alfalfa planting years.【Method】We investigated the soil physicochemical properties, ecological stoichiometric characteristics and enzyme activities at different growth years (2,3,4,5,6, and 7 years) and across various soil layers (0~20,20~40,40~60,60~80 and 80~100 cm) in the Hexi Irrigation District. We analyzed the effects of planting duration and soil layer depth on the soil physicochemical properties, ecological stoichiometric characteristics, and enzyme activities.【Result】1) Soil bulk density and porosity initially increased and then decreased with the extension of planting years. In a 5-year-old alfalfa grassland, soil bulk density was relatively high in the 40~60 cm soil layer (1.76 g·cm^-3), while in a 7-year-old alfalfa grassland, soil porosity was relatively high in the 60~80 cm soil layer (51.29%). 2) As the alfalfa planting years increased, the soil organic carbon (SOC) content gradually rose, while the average values of soil total nitrogen (TN) and total phosphorus (TP) content showed an initial increase followed by a decline. In this study, the soil C:N ratio ranged from 4.81 to 28.85. Except for a few deep-layer samples in certain years, the C:N ratio was higher than the national average (13.3), indicating relatively low soil N content. Meanwhile, the C:P and N:P ratios ranged from 1.53 to 19.54 and 0.19 to 1.12, respectively, both below the national averages (136 and 9.30). 3) Soil enzyme activity exhibited an initial increase followed by a decrease with the extension of planting years. Specifically, sucrose enzyme activity peaked in the 3rd year, increasing by 47.87% compared to that in the 2-year-old alfalfa field. Meanwhile, catalase and urease activities reached their highest levels in the 6th and 5th years, with increases of 66.67% and 17.07%, respectively, relative to the 2-year-old alfalfa field.【Conclusion】Alfalfa fields begin to deteriorate by the 6th year of planting, so plant for 5 years for best results and supplement the alfalfa field with fertilizer.