Qing YANG, Zisheng YANG

Institute of Land & Resources and Sustainable Development, Yunnan University of Finance and Economics, Kunming 650221, China

Cultivated lands are of close relationship with food security.Yunnan is the most southwestern province in China. Situated in a mountainous area, farmlands in Yunnan are generally poor in terms of quality and dominated by slope farmlands. Therefore, Yunnan is challenged by crop safety. According to the Second National Land Survey in 2009, the research measured pressure index of cultivated land and graded it in Yunnan in order to explore farmland tensions in Yunnan, laying foundation for determination of farmland reserve and formulation of farmland protection countermeasures.

Research Methods

Measurement of pressure index on cultivated land

The research modified farmland pressure index model[1]and computed alarming value per capita and farmland pressure index to further grade farmland,as follows:capita(hm2);Ds refers to self-sufficiency rate of crop (%); Fcis consumed quantity of crop per capita (kg per person); Yais annual yield per unit area (kg/hm2·a); Rsrepresents the percentage of total cropped grain area to total cropped area.

where Sminrefers to alarming value per

where K refers to farmland pressure index;Sminrefers to alarming value per capita (hm2); Sarepresents practical farmland area per capita(hm2).

Considering terraced fields and steep slopes are more in Yunnan, it is necessary to take the feasibility and eco-environment protection in changing steep slopes to terraced fields. For example, it is ruled slopes with slope over 25° should be returned to farmlands. Hence, slope farmlands with slope over 25°were omitted in the research. When K＞1, it means that the value of practical lands suitable for cultivation is lower than the alarming value,so that farmland pressure would be heavier. Consequently, it is of high possibility that crop crisis would occur.

Grading of pressure index on cultivated land

Currently, none researches available are on grading system and standards of farmland pressure and most analyses confine to specific pressure degree. In other words, assuming farmland pressure index of 1 as a boundary,if farmland pressure is higher than 1, it means farmland pressure is heavy. In the research, farmland pressure was graded into five grades,including without pressure, alarming pressure, lower pressure, moderate pressure and high pressure. Meanwhile the classification standards and concept wre determined of farmland pressure grades(Table 1).

Data source

The basic data of population and grains of the prefecture-level divisions of Yunnan were from Yunnan Statistical Yearbook in 2010 in Yunnan Province[2]and farmland data were from Land Variation Survey in 2009 by Department of Land Resources of Yunnan Province. With consideration of government work reports from different prefecture-level divisions, the research determined self-sufficiency rate of crops of 100% and consumption quantity of crops per capita of 400 kg,which is a little bit higher than crop consumption standards of primary well-off society[3].The base maps used in Arcgis and GeoDa contained maps in the format of shapefile, involving economic and administrative divisions.

Results and Analysis

Pressure index on cultivated land

According to the model above,alarming value of farmland per capita, farmland surplus or deficit per capita, and farmland pressure index can be concluded in Yunnan Province(Table 2).

As shown in Table 2, farmland pressure in different prefecture-level divisions tended to be volatile. Of the 16 divisions,the practical area of lands suitable for cultivation per capita kept larger than farmland alarming value per capita only in Qujing,Baoshan and Dehong, where farmland per capita was in surplus. In the rest divisions,however, farmland per capita had deficit. Specifically, farmland pressure in Dehong was the lowest, and the pressure index reached 0.8839, which was significantly lower than that of Yunnan Province (1.318 0).Farmland pressure index of Kunming, the capital of Yunnan Province, kept the highest of 2.355 6, under influence of economic and social aspects. Nujiang, situated in northwestern Yunnan Province,has limited lands suitable for cultivation, and farmland pressure index was as high as 2.3227. Because of dense population and limited quantity of fertile farmlands, farmland pressure index of Zhaotong was higher of1.903 6.

Grading of pressure on cultivated land

As shown in Fig.1, of the 16 Citylevel divisions, farmland pressure grade of Dehong was the least; the farmland pressures of Qujing and Baoshan maintained at critical state;farmland pressure grades all belonged to grade Ⅲof Lijiang, Pu’er, Lincang,Chuxiong, Honghe, Xishuangbanna,Dali and Diqing;farmland pressures of Yuxi and Zhaotong reached higher, at moderate grade; farmland pressure of Kunming and Nujiang reached the highest grade. Such grading is under influence of geographical location,transportation, economic factors. For example, Kunming and Yuxi are cities developing the fastest, with superior location, convenient transportation,and advanced industry, so that farmland pressure proves heavy. Nujiang and Zhaotong are located in northwestern and northeastern Yunnan,where steep slopes scatter here and there. Therefore, farmland pressure keeps higher. Both of water and climate in Baoshan and Dehong are suitable for crop growth, which keeps farmland pressure lower.

Conclusions

The research computed farmland pressure indices of different prefecture-level divisions and conducted grading and spatial analysis on basis of data of Yunnan Province. Of the 16 divisions, the practical area of lands suitable for cultivation per capita kept larger than farmland alarming value per capita only in Qujing,Baoshan and Dehong, where farmland per capita was in surplus. In the rest divisions,however, farmland per capita had deficit.The average farmland pressure index of Yunnan reached 1.318 0,which indicated that farmland pressures all maintain moderate of different administrative divisions in Yunnan.However, farmland pressures tend to be volatile. For instance, farmland pressure index of Dehong was 0.883 9, which was significantly lower than that of Yunan of 1.318 0. Farmland pressures of Kunming and Nujiang reached grade Ⅴ, far exceeding alarming value of farmland pressure;farmland pressures of Yuxi and Zhaotong were high, and only second to Kunming and Nujiang; farmland pressure of Qujing and Baoshan were alarming grades, and farmland pressure kept critical stage;farmland pressure of rest regions maintained lower.It can be concluded that farmland pressure of border provinces can never be ignored, and it is necessary to take administrative and technical measures to guarantee crop safety.

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