湖南祁阳县土壤酸化主要驱动因素贡献解析

Quantitative Analysis of Driving-Factors of Soil Acidification in Qiyang County, Hunan Province

【目的】以湖南省祁阳县为例,定量化分析整个县域不同土地利用方式下土壤的致酸因素,为我国的红壤酸化防治提供理论依据。【方法】通过搜集大量公开发表的文献、统计年鉴等,获取施肥量、主要农作物产量和林木生物量,以及地上部不同部位的养分含量等数据,基于经典的H^+产生量的计算方法,解析氮循环过程、盐基离子吸收和酸沉降等三个关键过程的相对贡献大小。【结果】对于整个祁阳县域,氮循环(N)过程致酸贡献率为66.5%(65.3%—68.8%),盐基(BC)吸收为33.0%(30.1%—34.4%),酸沉降则仅为0.5%(0.3%—1.7%)。无论是农田还是林地,氮循环过程都是产生H^+的主要来源,是土壤酸化的主要驱动因素。3种土地利用方式中,单位面积旱地农田的H^+净产量(产酸量)最高,达到19.0 kmol·hm^(-2)·a^(-1),其次为水田(16.5 kmol·hm^(-2)·a^(-1)),林地的产酸量(3.2 kmol·hm^(-2)·a^(-1))最低,旱地农田产酸量约为林地产酸量的6倍。6种主要农作物体系产酸量存在很大差异,从10.1 kmol·hm^(-2)·a^(-1)到30.0 kmol·hm^(-2)·a^(-1)不等,产酸量从大到小依次为:大豆>油菜>花生>水稻>玉米>甘薯,油料作物(油菜、花生、大豆)产酸量普遍大于粮食作物(水稻、玉米、甘薯)的产酸量;6种不同农作物的氮循环过程和盐基吸收的致酸贡献差异较大,氮循环过程致酸贡献率范围为45.3%—78.3%,盐基吸过程为21.4%—54.2%。7种主要林地体系产酸量也存在很大差异,从2.0 kmol·hm^(-2)·a^(-1)到27.8kmol·hm^(-2)·a^(-1)不等,柑橘>板栗>油茶林>马尾松>杉木>竹>湿地松,经济林(柑橘、板栗、油茶林)产酸量普遍大于用材林(马尾松、杉木、竹、湿地松)的产酸量;7种林木体系的氮循环过程和盐基吸收的致酸贡献率差异较大,氮循环过程致酸贡献率范围为46.1%—80.8%,盐基吸过程为19.0%—53.3%。采用"长期定位试验+土壤缓冲曲线"相结合的方法验证了本研究采用的H^+产生量的计算方法,土壤pH的模拟值和实测值呈极显著正相关,均方根误差(RMSE)为0.15,两者之间吻合度较高。【结论】氮循环过程是祁阳县域土壤酸化的主控因素。土壤酸化过程总产酸量差异和致酸因素贡献的大小主要取决于土地利用方式、农作物种类和林地类型。

【Objective】In Qiyang County, Hunan Province which is a typical county of China, quantifying key acidity inducing factors could provide theoretical bases for combating soil acidification, and provide scientific and technological supports for red soil acidification remediation in China.【Method】To achieve our objective, data of fertilizer rate, biomass (or yield) of main crops and trees, and above-ground nutrient contents reported within the experimental site were obtained from a large number of published literatures and statistical yearbooks. We quantified the acidity-inducing factors (nitrogen cycling process, BC (base cation) absorption and acid deposition) based on classical mass and charge balance. Relative contributions of the three key processes were used to illustrate the dominant factor of the soil acidification in uplands, paddy fields and woodlands.【Result】For the whole county, nitrogen cycling process accounted for 66.5%(65.3%- 68.8%) of the total H+ production, base absorption accounted for 33.0%(30.1%-34.4%), and acid deposition accounted for 0.5%(0.3%- 1.7%). Regardless of the land use patterns, nitrogen cycling process was the main source of H+ production and main controlling factor of soil acidification. Among the three land use patterns, H+ net production of upland was the highest (19.01 kmol·hm-2·a-1), followed by paddy field (16.5 kmol·hm-2·a-1), and woodland (3.2 kmol·hm-2·a-1) as the lowest. H+ net production in dry farmland was about 6 times of woodland. H+ net production of 6 main crop systems varies from 10.1 kmol·hm-2·a-1 to 30.0 kmol·hm-2·a-1, and followed the order: soybean>rape>peanut>rice>corn>sweet potato. Acidity production of the economic crops (rape, peanut and soybean) was generally higher than that of the grains (rice, corn, sweet potato);contribution rate of acidity-inducing of nitrogen cycling process among 6 main crop systems varied from 45.3% to 78.3%, contribution rate of acidity-inducing of base absorption varied from 21.4% to 54.2%. H+ net production of 7 main woodland systems varied greatly from 1.96 kmol·hm-2·a-1 to 27.8 kmol·hm-2·a-1, and followed the order: citrus>chestnut>camellia oleifera abel>pine>fir>bamboo>slash pine. Acidity production of economic forest (citrus, chestnut and camellia oleifera abel) was generally higher than that of timber forest (pine, fir, bamboo and slash pine);contribution rate of acidity-inducing of nitrogen cycling process among 7 main woodland systems varied from 46.1% to 80.8%, and contribution rate of acidity-inducing of base absorption varied from 19.0% to 53.3%. The long-term field experiment combined with soil buffering curve technique was used to verify reliability of the calculation method of H+ production. The simulated value of soil pH was positively correlated with the measured value significantly, with root mean square error (RMSE) of 0.15, while anastomosis degree between the two was high.【Conclusion】 Nitrogen cycling process was the main controlling factor of red soil acidification in Qiyang County. The differences of total acidity production and contribution of acidity-inducing factors depended largely on land use patterns, crop types and tree species.