Evaluation Of Suitability For Rice In Xuanhan

Xuanhan county is located in southern Daba Mountains, northeastern Sichuan Basin. Xuanhan has a long history of rice cultivation due to the subtropical humid monsoon climate, topography, and other natural conditions. The local people have abundant experiences in rice plantation. There are also large areas for rice cultivation with a high total yield. However, the layout of rice plantation remains to be improved. Rice has advantage of high economic value and adaptability and offers large contribution to cultivation. To evaluate the suitability of soil for rice could provides a guideline for regulating rice plantation, developing regional economic, and improving regional farming structure.With the help of geographic information system (GIS) and statistics tools, the evaluation of soil suitability to rice was conducted in Xuanhan county. The main results were as follows:1. Twelve indicators, namely, soil organic matter, effective thickness of soil, dependability of irrigation, total N, soil texture, pH, cropping system, terrain position, parent material, slope, available P, and available K, were selected to evaluate soil suitability for rice using the Delphi method. The database was constructed based on GIS.2. The weight of each factor was determined by AHP (Analytic Hierarchy Process). Fuzzy mathematics method was used to set up membership functions in terms of their characteristics and influence on the quality of cultivated rice land. Meanwhile, the grid-vector data and the fuzzy comprehensive evaluation model were used to set the suitability index of rice. Based on the index of evaluation units, the rice field was divided into four grades:first-rank suitability zone (highly suitable for cultivation), second-rank suitability zone (suitable for planting), third-rank suitability zone (barely suitable for cultivation) and forth-rank suitability zone (not suitable for planting). The results showed that in the total of 33340 hm2 of paddy fields, the areas of third-rank suitability zone had largest area of 15429.8 hm2, representing the total area of paddy fields 46.28%; followed by secondary suitability area for rice growth, the area was 11348.9 hm2, accounting for 16.71% of the total area of paddy fields. The first-rank suitability zone has an area of 3677.4 hm2, accounting for 11.03% of the total paddy fields. Forth-rank area was 2883.9 hm2, accounting for 8.65% total area of paddy fields.3. All the 12 evaluation factors of the four suitable areas were classified and compared among different ranks. The factors of the first-rank suitability zone were superior to that of the second-rank zone. Generally, the order of the four zones was the first-rank suitability zone> the second-rank zone> the third-rank zone> the forth-rank zone. Overall, the factors of the first-rank suitability zone outperformed other zones and the factors of the forth-rank suitability zone were the worst including some extreme conditions, such as soil shallowness and leanness. The results showed good agreement with the local soil conditions.4. The distributions of suitability zones at town scale. The first-rank suitability zone was mainly distributed in Qingxi, Nanba, Dacheng, Huangjin, Liuchi and Tiansheng. Among them, Qingxi had the largest area of 338.3 hm2, accounting for total area of 9.20%. However, no first-rank suitability zone was found in Dukou town and Fenglin. Therefore, high quality rice production base was recommended to be built in these towns. The second-rank and third-rank suitability zones were distributed in all towns. Nanba, Qili, Huangjin, Qingxi, Baishu, Tiantai, Tiansheng, Xiaba, Dongxiang, Shuanghe, Fengcheng, Puguang, and Bajiao had areas of more than 300 hm2. Nanba had the largest second-rank suitability area of 1096.3 hm2, accounting for total area of 9.66%. The third-rank suitability zone was mainly distributed in Dongxiang, Chahe, Aikou, Sanhe, and Qingxi. Some measurements should be taken to improve the suitability of soils in these towns. The forth-rank suitability zone mainly distributed in Tahe, Bajiao, Chahe, Fenglin and Nanba.