Tingwu LlP，Cong Ll，Weinan ZHAO，Yongzhao YANG，Jie ZHANG，Jianming XP，Yuming LPO

1.School of Life Science，HuaiYin Normal UniversitY/Jiangsu KeY LaboratorY for Eco-Agricultural BiotechnologY around Hongze Lake，Huai’an 223300，China；

2.Huai’an Soil fertilizer technical guidance station，Huai’an 223300，China

Analysis of Soil Acidification Trend on the South Bank of Hongze Lake during Recent 30 Years

Tingwu LlP1*，Cong Ll1，Weinan ZHAO1，Yongzhao YANG2，Jie ZHANG2，Jianming XP1，Yuming LPO1

1.School of Life Science，HuaiYin Normal UniversitY/Jiangsu KeY LaboratorY for Eco-Agricultural BiotechnologY around Hongze Lake，Huai’an 223300，China；

2.Huai’an Soil fertilizer technical guidance station，Huai’an 223300，China

Based on soil monitoring data in nine sites of Jinhu，XuYi and Hongze counties on the south bank of Hongze Lake from 1982 to 2013，changes in soil pH，total nitrogen （TN）content，available phosphorus content，organic matter（ON）content and cation exchange capacitY （CEC）were analYzed.The results show that due to excessive application of chemical fertilizer in soil on the south bank of Hongze Lake，soil pH reduced bY about 2 on average，while TN content and available phosphorus content in soil increased bY more than one time and 2-5 times respectivelY.Soil acidification caused bY agricultural production was verY serious.ln addition，low soil pH resulted in serious loss of soil cation，so that soil CEC in 2013 accounted for less than 50%of that in 1982 and affected mineral nutrient metabolism of crops.Therefore，application of calcium，potassium and trace-element fertilizer should be paid more attention to during agricultural production in future.

Hongze Lake；Soil acidification；Nitrogen and phosphorus content；Cation

l n recent several decades，soil acidification has become a serious ecological environment problem all over the world［1］.ln China，90% of farmland has suffered soil acidification to some degree，and the soil pH has decreased bY about 0.5 on average，that is，acid content in the soil has increased bY 2.2 times［2］.Soil acidification is closelY related to acid deposition in the atmosphere and excess application of nitrogen fertilizer.People have paid more attention to soil acidification caused bY acid deposition instead of excess application of nitrogen fertilizer.However，recentstatistics show soil acidification caused bY excess application of nitrogen fertilizer is verY serious in comparison to soil acidification［3］.Area of farmland in China accounts for 7%of total area of farmland in the world，but it has consumed 35%of fertilizer since the 1980s.From 1981 to 2008，grain output increased from 0.325 billion to 0.529 billion tons in China，rising bY 63%，while the usage of nitrogen fertilizer improved bY about two times.Excess application of chemical fertilizer has not increased crop Yield but has quickened soil acidification，and it has limited agricultural development at present［4］.

According to the surveY data obtained bY Jiangsu Department of Environmental Protection in 2009，soil acidification has appeared in most areas of Jiangsu Province，and it is the most serious in Taihu basin；soil tends to become acid in Lixiahe region and areas on the south bank of Hongze Lake［5］.Here based on the monitoring data of soil in nine monitoring sites in Jinhu，XuYi and Hongze counties on the south bank of Hongze Lake in recent 30 Years，soil acidification trend and changes in soil phYsical and chemical properties in the regions were analYzed to theoretical refer-ences for agricultural production and control of soil acidification in regions on the south bank of Hongze Lake.

Materials and Methods

SamPle collection and analysis

Soil samples were collected from nine monitoring sites in Jinhu（Huai village in Qianfeng Town，Nagang Village in Jinbei Town，and Agricultural TechnologY Center），XuYi（Heshan Village in Guantan Town，Heqiao Village in Heqiao Town，and Longdunkou Village in GuanYinsi Town）and Hongze（Xunhe Village in Gaojian Town，QingYun Village in Dongshuanggou Town，and Shitang Village in Chahe Town）counties on the south bank of Hongze Lake in 1982，2007，2011 and 2013.Soil pH，total nitrogen（TN）content，available phosphoruscontent，organic matter （ON）content and cation exchange capacitY（CEC）were determined respectivelY.Data in 1982 were obtained through the second national soil surveY.

Statistical analysis

Data processing and statistics were conducted using SPSS software.

Results and Analysis

Changes of soil PH

As shown in Fig.1，soil pH in main monitoring sites on the south bank of Hongze Lake showed a decreasing trend since 1982，reducing bY 1.5 on average.Soil pH declined most greatlY in Gaojian Town，Hongze，so its acidification trend was most obvious.Soil pH in China’s croplands decreased bY 0.5-0.8 on average［2］.lt is clearlY seen that soil acidification in regions on the south bank of Hongze Lake was more serious than the national average，and the acidification trend was extremelY obvious.Wang Zhiguang et al.pointed out that soil pH in Jiangsu Province in 1980 and 2003 declined greatlY，which is consistent with the result above［5］. From 2011 to 2013，soil pH decreased slightlY in XuYi CountY but was stable in other counties.lt reveals that soil acidification has paid more attention to daY bY daY in recent Years，and necessarY measures has been adopted to prevent soil pH from reducing further［6］. Variations of nitrogen and Phos-Phorous content in soil

Fertilizer applied in farmland is far more than the demand for crop growth for a long time，so that excessive nitrogen has accumulated in soil［7］.According to Fig.2，TN content in soil in main monitoring sites on the south bank of Hongze Lake increased from 1982 to 2013，rising bY more than one time.EspeciallY in 1982-2007，it varied obviouslY，and TN content in soil in XuYi and Hongze counties increased rapidlY.During 2007-2013，there was no obvious change in TN content in soil，because the usage of nitrogen fertilizer in farmland has been controlled since soil acidification has been paid more attention to［8］.ln Jinhu CountY，TN content in soil showed an increasing trend from 1982 to 2013.lt is found that soil was uncultivated in Huai Village and Agricultural TechnologY Center before 2007，and then food crops were planted here，so TN content in soil was not up to the threshold value.

Similar to TN content in soil，available phosphorus content in soil also showed an increasing trend from 1982 to 2013 （Fig.3）.The maximum appeared in 2007 in most stations，rising bY above two times compared with 1982，and the increase reached 3-5 times in Agricultural TechnologY Center，Longdunkou Village and Hongze CountY.Noreover，available phosphorus content in soil reduced temporallY from 2007 to 2011 and then increased slightlY in most stations.However，due to residue of phosphoric acid in soil，available phosphorus content in soil was still high in a short time［4］.

Changes of organic matter content in soil

Soil organic matter is an important source of nutrients in soil，and organic matter content in soil is a keY indicator of soil fertilitY［9］.As shown in Fig.4，ON content in soil in main monitoring sites on the south bank of Hongze Lake increased obviouslY from 1982 to 2013，rising bY more than one time in most stations.ON content in soil increased rapidlY during 1982-2007 and then slowlY in 2007-2011 in most stations，and it decreased greatlY in four stations in XuYi and Hongze counties even.lt is seen that excessive cultivation or nutritional imbalance will lead to loss of soil fertilitY after soil fertilitY reaches a certain threshold value.

Variations in soil cation exchange caPacity

According to Fig.5，soil CEC in main monitoring sites on the south bank of Hongze Lake declined obviouslY from 1982 to 2013，that is，soil CEC in 2013 accounted for 40%-51% of that in 1982，which is consistent with the changing trend of soil pH.Due to soil acidification，cation in soil has been displaced and lost out of farmland ecosYstem with surface runoff［10］.

Discussion

Soil acidification caused bY agricultural production has not been paid more attention to，and more and more studies show that excessive application of fertilizer has led to reduction of ON content in soil hardening.OnlY 35%of fertilizer has been used bY crops in China，and most fertilizer applied in farmland is left in soil.Results in the studY reveal that TN content in soil in nine monitoring sites of three counties on the south bank of Hongze Lake increased bY more than one time，and available phosphorus content in soil rose bY 2-5 times from 1982 to 2013.

Through nitrification and denitrification，nitrogen fertilizer can produce nitrate in soil，and ammoniacal nitrogen and organic nitrogen fertilizer will release protons into soil during the process of transformation into nitrate，therebY resulting in soil acidification［11］. ln addition，when plants absorb NH4+from phYsiological acidic fertilizer（such as calcium phosphate，ammonium sulfate and ammonium chloride），protons are released from roots to soil，so large quantities of protons in soil can lead to decline of soil pH［8，12］.ln the studY，soil pH in the nine sites reduced from 7.0 to 5.0，so soil acidification was verY serious and must be valued.

Besides affecting crop growth，soil acidification can change cation content and composition in soil through proton exchange.ln the studY，soil CEC in the nine sites decreased from 30 to 12 cmol/kg，reducing bY more than 50%. lt is seen that soil acidification results in loss of cations and then influence crop growth.Previous studies show that excess fertilization can lead to shortage of Ca，Ng，K and other trace elements［2，7，13-15］.Therefore，application of calcium，potassium and trace-element fertilizer should be valued during agricultural production in future.

ln the studY，soil pH，nitrogen and phosphorus content in soil in the nine sites were stable after 2007，indicating that worse consequences caused bY excessivelY extensive agricultural production mode have paid close attention to bY the government and related departments.AdditionallY，after more than 20 Years of development agricultural production technologY has been improved，and the government has adopted required measures such as returning straw to soil［16］，reduction of chemical fertilizer application and increase of organic fertilizer application［6］，which has limited further deterioration of soil acidification［17］.Seen from soil CEC，soil pH in the nine sites was low，and cation and other nutrients still lost in a short term，so it maY need a long time to control soil acidification［18］.

Conclusions

ln the nine monitoring sites of Jinhu，XuYi and Hongze counties on the south bank of Hongze Lake during 1982-2013，soil pH showed an obvious decreasing trend，reducing bY 2 on average.lt reveals that soil acidification was serious in these regions and should be paid more attention to. Neanwhile，TN content and available phosphorus content in soil increased bY more than one time and 2-5 times respectivelY， showing that large amounts of nitrogen and phosphorus fertilizer has accumulated in soil.ln addition，soil CEC in 2013 accounted for less than 50%of that in 1982 in most sites and affected crop growth，so application of calcium，potassium and trace-element fertilizer should be increased during agricultural production in future.

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ResPonsible editor：Yingying YANG

ResPonsible Proofreader：Xiaoyan WP

洪澤湖南岸近30年來土壤酸化趨勢分析

劉廷武1*，李聰1，趙偉男1，楊用釗2，張杰2，徐建明1，羅玉明1（1.淮陰師范學院生命科學學院/江蘇省環(huán)洪澤湖生態(tài)農(nóng)業(yè)生物技術重點實驗室，江蘇淮安223300；2.江蘇省淮安市土壤肥料技術指導站，江蘇淮安223300）

利用洪澤湖南岸的金湖、盱眙和洪澤3縣的9個土壤監(jiān)測點近30年土壤相關監(jiān)測數(shù)據(jù)，分析土壤pH值、土壤全氮含量、有效磷含量、有機質含量及陽離子交換量等指標變化。結果表明，由于過量化肥的施用，30年來洪澤湖南岸地區(qū)土壤pH值普遍下降2左右，土壤中全氮含量增加了1倍以上，有效磷含量增加了2～5倍，農(nóng)業(yè)生產(chǎn)導致的土壤酸化問題十分明顯。低pH值導致該地區(qū)土壤陽離子流失嚴重，其陽離子交換量不足原來的50%，已對作物的礦質營養(yǎng)代謝帶來危害，應在本地區(qū)重視鈣肥、鉀肥及其他微量元素肥料的投入使用。

洪澤湖；土壤酸化；氮磷含量；陽離子

江蘇省高校自然科學研究面上項目（13KJB210001）；江蘇省高等學校大學生創(chuàng)新訓練計劃項目（201310323040Y）；江蘇省淮安市科技支撐計劃（SN13049）。

劉廷武（1984-），男，河北張北人，講師，博士，從事作物生理生化及土壤肥料研究，E-mail：liutw@hytc.edu.cn。*通訊作者。

2015-06-26

Supported bY the Surface Project of Natural Science Research for Higher Education in Jiangsu Province（13KJB210001）；lnnovation Planning Project for UniversitY Students in Jiangsu Province （201310323040Y）；KeY TechnologY R&D Program of Huai'an CitY，Jiangsu Province（SN13049）.

*Corresponding author.E-mail:liutw@hYtc.edu.cn

Received:June 26，2015 Accepted:September 8，2015

修回日期 2015-09-08