Jie PAN，Xiongjie LV，Hui XlAO，Wenlong LU.Tianjin Institute of Agricultural Resources and Environment Science，Tianjin 0084，China；.Information Institute of Tianjin Academy of Agricultural Sciences，Tianjin 009，China；.Tianjin Academy of Agricultural Sciences，Tianjin 009，China

Spatial-Temporal Distribution Characteristics and Limiting Factors of Medium-low Yield Farmland in Tianjin

Jie PAN1，Xiongjie LV2，Hui XlAO1，Wenlong LU3
1.Tianjin Institute of Agricultural Resources and Environment Science，Tianjin 300384，China；
2.Information Institute of Tianjin Academy of Agricultural Sciences，Tianjin 300192，China；
3.Tianjin Academy of Agricultural Sciences，Tianjin 300192，China

［Objective］This paper aimed to understand the area change and distribution of medium-low yield farmland，and offered basis to the improvement of mediumlow farmland and its increase of grain production in Tianjin.［Method］Based on the statistical date of Tianjin and its relevant counties and districts，the yield standard was set up to classify high-yield，medium-yield and low-yield farmland in Tianjin. The author analyzed area change of medium-low yield farmland in six agricultural counties and districts（including Jixian County，Wuqing District，Baodi District，Ninghe County，Jinghai County and Dagang of Binghai New Area）from 1980 to 2010.［Result］The results showed that the average yield of grain rose from 2 445 kg/hm2in 1980 to 5 130 kg/hm2in 2010，increasing 109.82%.The area of medium-low yield farmland was reduced from 291 250.13 hm2in 1985 to 76 489.87 hm2in 2010，coming down 74%.In Tianjin，the area of medium-low yield farmland of 2010 accounted for 19%of the total farmland，of which the ratios of medium-low yield farmland of Jinghai County，Jixian County，Dagang of Binghai New Area，Wuqing District，Baodi District and Ninghe County were 43.12%，18.59%，17.23%，14.01%，7.05%and 0，respectively.Low soil nutrient content，drought and water shortage，as well as soil salinization were the main yield limiting factors to medium-low yield farmland in Tianjin in 2010.［Conclusion］The countermeasures to improve the medium-low yield farmland were proposed，involving enhancing the investment of the government，strengthening the construction of water conservancy infrastructure，further improving the soil fertility，as well as saline and alkaline land，optimizing the farming system and planting drought and salt tolerance crops，etc.

Medium-low yield farmland；Spatial-temporal distribution；Limiting factors；Tianjin

F ood security closely relates to social stability in China and the livelihood of Chinese.In recent years，with the development of industrialization and urbanization in China，a plentiful acre of cultivated land has been occupied，which makes the original limited cultivated land even less. To deal with the growing demands for crops，the rural work committee in 2013 pointed out that solving the food problem should be the primary issue for Chinese government.

In order to make sure that the crops in China is plenty enough for Chinese to eat，it is imperative to protect the 1.8 billion acre of cultivated land，and to take actions to enhance the comprehensive production of crops.According to statistics，more than two thirds of cultivated land is of low yield，which suggests that there is huge potential to increase the yield，while to explore the productive potential of the current farmland is an essential way to realize the dynamic balance of total farmland and to ensure the food security in China，and a must to attain the sustainable use of land resources and economic development［2］.

Tianjin lies closely to Bohai Sea，featuring high soil alkaline degree，scarce freshwater resources，poor soil quality，low crops yield and large acre of medium-low yield farmland.Exploring the production potential of medium-low yield farmland in Tianjin is of great significance to the ecological environment，while understanding the types of medium-low yield farmland and its regional distribution is the foundation and premise to ameliorate the medium-low yield farmland.Some researchers have conducted primary investigation of the total distribution and quality of farmland，but there is not any report regarding the medium-low yield farmland and its regional distribution in Tianjin.

Based on the previous studies，and the standards for high，medium and low yield farmland，it is important to discuss the dynamic changes of medium-low yield of farmland in six counties and the major factors which limit the spatial distribution of mediumlow yield farmland in Tianjin，as well as to put forward corresponding suggestion in order to provide theoretical basis for the amelioration of medium-low yield of farmland and growth in crops production.

Materials and Methods

Determination of study subjects

The common farmland in Tianjin at the end of 2010 amounts to 56 654 hm2（including Dongli district 9 893 hm2，Jinnan district 14 140 hm2，Xiqin district 14 190 hm2and Beichen district 18 431 hm2），accounting for 14%of the total common farmland in Tianjin at the end of 2010（398 793 hm2）［4］.Besides，because of the special location of four districts，most parts of the farmland are used to plant vegetables，and only 40%farmland plants crops［5］.Therefore，this paper studies the mediumlow yield farmland in Jixian County，Wuqin District，Baodi District，Ninghe County，Jinhai County and New Binhai District in Tianjin in the last three decades.

Division of high，medium and low farmland

The classification of medium-low farmland includes output method，limiting factors and land level［6-8］.Output method is to divide the farmland based on units of crop output，including average output method and potential output rate.Such method is easy to operate，and easy to access to data.Limiting factors is to classify the farmland based on the premise whether there is any limiting factor and on the level of limiting factors so that the medium-low yield farmland can be divided as arable land，drought land，alkaline land，sandy land and waterlogged land，etc.［9］Limiting factors can reveal factors influencing crops output，which can provide reference to reform the medium-low yield farmland.Land grading method considers realistic production level， irrigation condition，farmland property，farmland density，nutrition content，farmland gradient，as well as water and soil erosion as the indicators to grade the farmland.Land level method composes almost every aspect of farmland quality，including output factors，internal and external conditions of farmland.

At present，the division of high and medium-low yield farmland is based on crops output［10］.In the nationwide resources investigation carried out in 1990，the medium-low yield farmland is classified based on the average standard yield in three years［2］. The expansive land in China results in huge differences in the natural and social economic conditions which affect the crops output，so different places have different standards.For instance，Shanxi Province listed the land with the yield of less than 2 250 kg/hm2as low yield land and 2 250-4 500 kg/hm2as medium yield land.The Hetao area in Inner Mongolia listed the land with the yield of less than 300 kg/hm2as low yield land，and 3 000-4 500 kg/hm2as medium yield land［11］.Jianghan Plateau and Northern Hubei regarded the land with the yield less than 4 500 kg/hm2as the low yield farmland. Jiangsu Province considered the land with the yield less than 7 500 kg/hm2as low yield land，and 7 500-9 000 kg/hm2as medium yield farmland［12］.

1992 witnessed Tianjin Agricultural Division Committee revising the three-year annual yield per acre around 20%as moderate yield land，higher than 20%as high yield land，and less than 20%as low yield land. According to this standard，each district and county in Tianjin has made its own output standard.Because of different output levels，the standard in each county varies a lot，such as the low standard in Jixian County less than 6 000 kg/hm2，Wuqing less than 5 250 kg/hm2，Dagang and Jinghai less than 2 250 kg/hm2.Based on these studies and the realistic situations in Tianjin，if the average output of crops in the town is 15%higher than the average output in Tianjin，it is high-yield farmland，and if the average output of crops in the town is 15%less than the average output in Tianjin，it is low-yield farmland，and other data are considered as medium yield farmland.

Data collection and statistics

Basic data collection This paper chooses six major agricultural districts and counties in Tianjin，and collects the Statistics Yearbook of Tianjin（1981，1986，1991，1996，2001，2006 and 2011）as well as the Statistical Yearbook of Related Districts and Counties （1980，1985，1990，1995，2000，2005 and 2010），including the farmland in each town，planting area and output of crops in each town，output of crops in each district.

Calculation of the land with high，moderate，and low-yield output

The land with high output refers to the total of all farmland in the town with high-yield land.The land with low output means the total of all farmland in the town with low-yield land.The land with moderate output refers to the total of all farmland in the town with moderate output.

Selection of limited factors When we divide the farmland with moderate and low output，it is necessary to investigate the soil types，land condition，irrigation capacity，planting policy，and current planting crops，and the output in the normal year.Spatial analysis was conducted to determine the main limiting factors based on the soil nutrition level standard，irrigation condition，and the salt content in the soil recommended by the second national general survey of soil.

Results and Analyses

Average output of crops in Tianjin and other six counties from 1980 to 2010

The average output of crops in six districts in Tianjin from 1980 to 2010was shown in Table 1.The average output of crops in Tianjin rose by 109.82%from 2 445 kg/hm2in 1980 to 5 130 kg/hm2in 2010.

Table 1 The average crops output in Tianjin and six main agricultural districts and counties in Tianjin

Changes of land with moderate and low yield in six districts in Tianjin from 1980 to 2010

Changes of land with moderate and low yield in six districts in Tianjin from 1980 to 2010 were shown in the Fig.1.

As we can see from the Fig.1，the land with moderate and low yield in the six districts in Tianjin showed a downward trend between 1980 and 2010，decreasing by 74%from 291 250.13 hm2in 1980 to 76 489 hm2in 2010，which might be the result of gradually improved agricultural irrigation condition，continuous decreasing alkaline land，and continuous advancement of science and technology.The land with moderate and low yield in 2000 was higher than that in1995，as the drought in Tianjin in 2000 led to reduction in crops output.

In the recent 30 years，although the land with moderate and low yield in Tianjin decreased，the land with moderate and low yield still amounted to 76 489.87 hm2until 2010，which accounted for 19%of the total farmland in Tianjin （398 793 hm2in 2010）. Therefore，the mission to reform the land with moderate and low yield was still tough.

Spatial distribution of the land with moderate and low yield in six districts in Tianjin in 2010

The land with moderate and low yield among different districts and counties in Tianjin varied distinctively. The land with moderate and low yield ranged as Jinhai，Jixian，Binhai new district，Wuqing and Baodi district. There was no moderate and low yield land in Ninghe County in 2010.There were 32 981 hm2of land with moderate and low yield in Jinhai County，which accounted for 43.21%of total moderate and low yield land，covering Jinhai Town，Wangkou Town，Chenguantun Town，Daqiuzhuang Town，Caigongzhuang Town，Liangtou Town，Xizhaizhuang Town，Liangwangzhuang Village，Zhuangchengzhuang Town，and DafengduiTown.There were 14 218.13 hm2of land with moderate and low yield in Jixian Count，which occupied 18.59% ，covering Yuyang Town，Guanzhuang Town，Mashenqiao Town，Xiaying Town，Xiacang Town，Luozhuangzi Town，Wubaihu Town，Xilonghuyu Town，Chuanfangyu Town，Xujiatai Village and Sungezhuang Town.There were 13 180.13 hm2of land with moderate and low yieldof crops in Binhai new district， which took up 17.23%of total land area，covering Taipin Town，Xiaowangzhuang Town， Zhongtang Town and Gangxi Street.There were 10 716.33 hm2of land with moderate and low yieldof crops in Wuqing District，which represented 14.01%of the total land，covering Meichang Town，Dahuangbao Village， Dajiachang Town and Wangqingtuo Town.There were 5 394.27 hm2of land with moderate and low yieldof crops in Baodi District，which constituted 7.05%of total moderate and low yield land，mostly in Gaojiazhuang Town and Shigezhuang Town.

Based on the land use in Tianjin in 2010，the farmland distribution in Tianjin was shown in Fig.2.According to Fig.2，there was moderate and low yield farmland from the north to the south，but mostly in Jinhai County，accounting for 43.12%of the total land with moderate and low output.

Analyses of main limiting factors of moderate and low output land in Tianjin

Crops growth depends on its satisfactory of the environment to its optimal growing surrounding value.According to the bucket principle，under certain technological condition，the productivity of moderate and low yield farmland was determined by main limiting factors.When we compare the satisfactory of each surrounding factors，factors with little satisfactory were the primary limiting factors that influence the growth of crops，and formed the main reason for moderate and low yield.The smallest satisfactory degree was the first limiting factor，followed by the second limiting factor and so on［8］.

Table 2 Standard of nutrition in the soil in the secondary national survey

Taking GIS as the technological measure，the spatial distribution of moderate and low yield farmland in Tianjin overlapped with the stationswhose farmland production was surveyed in Tianjin.The content of organic matters in the soil，the content of nitrogen，available potassium，and available phosphorus，alkaline，and irrigation capacity were considered as indicators to conduct quantity analysis of the main limiting factors of moderate and low output in Tianjin.

According to the soil nutrition grade standard recommended by the second national soil survey（Table 2），we conducted statistical analyses to the moderate and low yield farmland whose organic matters in the soil，the content of nitrogen，available potassium，and available phosphorus were in the third to six grade.There were 56 302.4 hm2of land whose organic content in the soil was less than 3%，53 102 hm2of land whose nitrogen content in the soil was less than 0.15%，25 011.93 hm2of land whose available potassium content in the soil was less than 150 mg/kg，35 376.67 hm2of land whose available phosphorus was less than 20 mg/kg.There was 9 990.07 hm2of land without irrigation condition.There was 7 732 hm2of land whose salt content was larger than 2‰ .Comprehensive analysis suggested that low content of nutrition in the soil and water shortage as well as soil alkaline was the major limiting factors for moderate and low yield farmland.

Conclusions and Discussions

Reforming the moderate and low output farmland means to take technological measures and invest in infrastructure to improve agricultural production to deal with the factors which limit the development of production capacity so that the low yield farmland will turn into moderate yield farmland，and the moderate yield farmland will become high yield farmland［13］.This study has found that in the thirty years between 1980 and 2010，with the advancement of scientific technology and economic development，the average output of crops in Tianjin increased by 109.82%，and the land with moderate and low yield in Tianjin decreased by 74%from 291 250.13 hm2in 1980 to 76 489.87 hm2.The land with moderate and low yield in Tianjin ranked from Jinhai County，Jixian County，Binhai New District，Wuqing District，Baodi District and Ninghe County，with the low yield land accounting for 43.12%，18.59%，17.23%，14.01%，7.05%and 0 of the total moderate and low yield. There was huge potential in enhancing the moderate and low yield farmland. If the moderate and low output farmland increases 750 kg of crops per acre per year，there will be an increase of 57 367.402 t of crops in Tianjin.

Based on the analysis of the limiting factors for the crops growth，low content of nutrition in the soil and water shortage as well as soil alkaline was the major limiting factors for moderate and low yield farmland.

Reforming the moderate and low output farmland is a complicated process that needs large amount of technological and political support.Several suggestions have been put forward as follows.

First of all，political guidance and financial investment need to be strengthened.There is a huge potential in increasing crops output to ensure food safety.At present，financial shortage is an important factor to limit the reform of moderate and low yield farmland in China.

Secondly，farmland infrastructure and hydraulic facilities need to be enhanced.The basic construction of farmland is an essential work to do. One is to ameliorate the supporting facilities and to repair the broken machine，and the other is to promote irrigation technology.The third measure is to carry out water conservation and utilization to ease water shortage.

Thirdly，improving soil structure. One is to increase the input of organic fertilizer，to change the soil structure，and to enhance water conservation capacity.The second way is to fertilize the land based on the soil nutrition property and crops features［15］.It is essential to satisfy the demand for different nutrition in the crops development，and to reduce pollution［16］.

Fourthly，salt management and alkaline treatment.Tianjin lies around Bohai Sea，and the high alkaline level in the soil restrain the crops development，which can be solved by improving the irrigation system，and using organic and nonorganic conditioner to change the soil structure.

Fifthly，the cultivation policy can be optimized by planting refined species.In order to realize sustainabledevelopment，its core is scientific and reasonable cultivation policy.The alkaline land and less precipitation make it more important to promote droughtresistant and salt-tolerant species to enhance crops yield.

References

［1］LI MQ（李明秋），HAN TK（韩桐魁）.Reforming the moderate and low yield farmland and sustainable use of land resources（论中低产田改造与土地资源的可持续利用）［J］.Chinese Journal of Population Resources and Environment（中国人口资源与环境），2001，11（51）: 24-25.

［2］ZHANG L（张琳），ZHANG FR（张凤荣），JIANG GH（姜广辉），et al.Potential to increase crops amount and food security by reforming low and moderate yield farmland in China中国中低产田改造的粮食增产潜力与食物安全保障 ［J］.Research of Agricultural Modernization（农业现代化研究），2005，26（1）:22-25.

［3］ZHANG YL（张余良），SUN CZ（孙长载），LI MY（李明悦）.Problems and current situation of cultivated land resources in Tianjin （天津农业耕地资源现状及存在的问题）［J］.Tianjin Agricultural Sciences（天津农业科学），2006，12（3）:38-41.

［4］Tianjin Survey Team of State Statistics Bureau （国家统计局天津调查总队）. Tianjin Survey Yearbook （天津调查年鉴）［M］.Beijing:China Statistics Press（北京:中国统计出版社），2011.

［5］Tianjin Statistics Bureau （天津市统计局）.Tianjin Statistics Yearbook（天津市统计年鉴）［M］.Tianjin:Tianjin Statistics Press（天津:天津统计出版社），2011.

［6］SHI QH（石全红），WANG H（王宏），CHEN F（陈阜），et al.The spatial-temporal distribution characteristics-lowand yield potential of medium-low yield farmland in China（中国中低产田时空分布特征及增产潜力分析）［J］.Chinese Agricultural Science Bulletin （中国农学通报），2010，26（19）:369-373.

［7］BI YY （毕于运）.Evaluation of several main dividing method of medium-low yield farmland （关于中低产田几种主要划分方法的评价）［J］.Chinese Journal of Agricultural Resources and Regional Planning（农业区划），1993（1）:57-60.

［8］ZHANG XL（张晓玲），XU BG（徐保根），FAN LY（樊兰瑛），et al.Studies on the medium-low yield farmland cause types（中低产田成因类型划分方法的研究）［J］. Resources Science（资源科学），1999，21（4）:35-38.

［9］LI EZ（李恩泽），LIU HF（刘海凤），WANG S （王肃）.Discussion on medium-low farmland classification and standard problems（关于中低产田类型划分与标准问题的探讨）［J］.Areal Research and Development （地域研究与开发），1992，11（2）:16-18.

［10］XIA JG（夏建国），WEI CF（魏朝富）.Research Review on the improvement of low-medium yielding farmlands in China（中国中低产田土改造研究综述）［J］. Chinese Agricultural Science Bulletin（中国农学通报），2005，21（4）:212-218.

［11］FAN RW（樊润威），CUI ZX（崔志祥），ZHANG SF（张三粉）.Grading mediumlow yield farmland in Hetao in Inner Mongolia（内蒙古河套灌区中低产田的分级）［J］.Soils（土壤），1995（2）:64-67.

［12］LI MQ（李明秋），HAN TK（韩桐魁），LV XM （吕学明）.Current situation of medium-low yield farmland reforming and political measures（中低产田改造的现状分析与政策措施）［J］.Journal of Huazhong Agricultural University（Social Sciences Edition）华中农业大学学报:社会科学版，2000，36（2）:11-14.

［13］LI PS（林鹏生）.Studies on medium-low farmland distribution and production growth potential in China （中国中低产田分布及增产潜力研究）［D］.Beijing: Chinese Academy of Agricultural Sciences（CAAS）.（北京:中国农业科学院），2008:50-103.

［14］LIAO Q（粱青），WANG XF（王晓峰），ZHA N（查娜）.Problems and countermeasures in reforming medium-low farmland in Chifeng City（赤峰市中低产田改造工作存在的问题与对策）［J］. Inner Mongolia Agricultural Sciences and Technology （内蒙古农业科技），2013（4）:69，92.

［15］Planting Department of Agricultural Department.National Agricultural Technology Promotion Service Center（农业部种植业司.全国农业技术推广服务中心）.Questions and answers regarding fertilizing technology （土配方施肥技术问答）［M］.Beijing:China Agriculture Press（北京:中国农业出版社），2005:1.

［16］ZHU HL（朱华龙），JIANG YM（蒋毅敏），YANG PQ（杨培权），et al.Current situations and countermeasures of medium-low yield farmland in five districts in Guilin （桂林市五城区中低产田的现状与改良措施）［J］.Anhui Agriculture（现代农业科技），2013（14）:225-226.

Responsible editor:Nana FAN

Responsible proofreader:Xiaoyan WU

（Continued from page 572）设备设计与应用）［M］.Beijing:Chemical Industry Press（北京:化学工业出版社），2003.

［15］LANGERGRABER G，HABERL R，LABER J，et al.Evaluation of substrate clogging processes in vertical flow constructed wetlands ［J］.Wat Sci Tech，2003，48（5）:25-34.

［16］YU T（于涛），WU ZB（吴振斌），XU D（徐栋），et al.Clogging mechanism and modelling of subsurface flow constructed wetland（潜流型人工湿地堵塞机制及其模型化）［J］.Environmental Science&Technology（环境科学与技术），2006，29（6）:35-37.

［17］NAN GY（南国英），ZHANG ZG（张志刚）.Water Supply and Drainage Engineering Process Design（给水排水工程专业工艺设计）［M］.Beijing:Chemical Industry Press（北京:化学工业出版社），2004.

［18］Beijing Municipal Engineering Design and Research Institute（北京市市政设计研究院）.Concise Drainage Design Manual（简明排水设计手册）［M］.Beijing:China Building Industry Press（北京:中国建筑工业出版社），1990.

［19］Ministry of Environmental Protection of the People’s Republic of China（中华人民共和国环境保护部）.HJ 2005-2010 Technical Specification of Constructed Wetlands for Wastewater Treatment Engineering（HJ 2005-2010人工湿地污水处理工程技术规范）［S］. Beijing:China Environmental Science Press（北京:中国环境科学出版社），2011.

［20］WU ZB（吴振斌），XIE XL（谢小龙），XU D（徐栋），et al.Application of integrated vertical flow constructed wetland for improvement of water quality of dragon-shaped water system in Beijing Olympic Forest Park（复合垂直流人工湿地在奥林匹克森林公园龙型水系的应用）［J］.China Water&Wastewater（中国给水排水），2009，24（12）:28-35.

Responsible editor:Tingting XU

Responsible proofreader:Xiaoyan WU

天津市中低产田时空分布与限制因素研究

潘 洁1，吕雄杰2，肖 辉1，陆文龙3*（1.天津市农业资源与环境研究所，天津 300384；2.天津市农业科学院信息研究所，天津 300192；3.天津市农业科学院，天津 300192）

［目的］为了解天津市中低产田面积变化情况及中低产田空间分布情况，为天津市中低产田改良及粮食增产提供基础依据。［yy if］以天津市统计年鉴及相关区县统计年鉴数据为依据，拟定了高、中、低产田划分标准，分析了天津市6个主要农业区县（蓟县、武清区、宝坻区、宁河县、静海县和滨海新区大港）1980～2010年30年间中低产田面积变化情况。［结果］［经过30年的不懈努力，天津市粮食平均产量由1980年的2 445 kg/hm2提高到2010年的5 130 kg/hm2，增加了109.82%。天津市的中低产田面积由1980年的291 250.13 hm2，下降至2010年的76 489.87 hm2，下降了74%。2010年天津市中低产田面积占全市耕地 总面积的 19%，其中静海县、蓟县、滨海新区大港、武清区、宝坻区、宁河县中低产田分别占全市中低产田总面积的43.12%、18.59%、17.23%、14.01%、7.05%和0。2010年天津市中低产田粮食增产限制因素分析 表明，土壤养分含量低、干旱缺水和土壤盐渍化是主要限制因子。［结论］建议继续加大政府资金投入、强化水利基础设施建设、进一步提高土壤肥力、综合改良盐碱地、优化耕作制度种植耐旱耐盐作物品种等工程与技术措施，持续改良中低产田。

中低产田；时空分布；限制因素；天津

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2014-12-20

2015-02-20

Supported by National Scientific and Technological Subject"Around Bohai District Tianjin Crops Growth Technological Integration and Demonstration"（2013BAD05B08）.

.E-mail:tjwllu@126.com

December 20，2014Accepted:February 20，2015