Assessing soil fertility index using Fuzzy-AHP and parametric methods for tea cultivation with different productivities

The rapid growth of population demands higher land use efficiency to ensure food security. The most appropriate way to reach this goal is to increase yield per unit area. In this regard, the assessment of soil fertility and productivity is a prerequisite for developing sustainable agriculture. Soil fertility indicates the soil capability to provide optimum conditions for plant growth. Assessing soil fertility is an essential need to identify environmental-friendly strategies leading to more sustainability in agricultural systems. Soil fertility directly and indirectly affects the yield and crop quality. In order for food security and increased food production to be achieved, the development of a useful method for assessing soil fertility and productivity is fundamental. Various modeling techniques have been proposed as a useful tool to determine soil fertility. An assessment of the soil fertility status by using a soil index could provide key information to improve strategies and effective techniques for the future to achieve sustainable agriculture. The present study was conducted: (1) to determine the soil fertility index (SFI) using two methods which are conceptually different from each other including: Fuzzy-AHP and parametric methods; (2) to identify the main soil limiting factors for tea production; and (3) to compare two methods of quantitative assessment of soil fertility in relation to tea yield in tea cultivation with different productivities in west Guilan province.Materials and Methods Based on the mean annual tea yield, the selected tea cultivation were divided into low, medium, and high productivity. Sixty-six soil samples were collected from 0 to 30 cm depth. The green tea leaves were harvested at a 2 m2 plot at each site. In this research, clay, silt, and sand content, mean weight diameter of soil aggregates, bulk density, soil pH, electrical conductivity, soil organic carbon, total nitrogen, available phosphorus, available potassium, available copper, and zinc were measured by conventional methods. Then, the soil fertility indices of tea cultivation with different productivities were determined by fuzzy-analytical hierarchy process (SFI-Fuzzy AHP) and Parametric (SFI-Parametric) analyses. The Fuzzy analytical hierarchy process is a combination of factor weights of AHP with the fuzzy values of each parameter. The product of values generated from individual fuzzification of parameters with their corresponding factor weights. All soil parameters were tested using one-way analysis of variance and the differences among means were analyzed using Tukey's significant difference test at the probability level of 0.05.The coefficients of determination for the linear regression between the two SFI values and tea yields were conducted.Results and Discussion Results indicated that the effect of pH, available potassium and copper, mean weight diameter, and bulk density on tea yield was significant (p <0.01). The highest of organic carbon, mean weight diameter, available potassium and copper were obtained in high productivity. The highest of soil pH and bulk density were related to low productivity. The main soil limiting factors for tea production were soil organic carbon, available potassium, and soil pH. The results showed that for both SFI-Fuzzy AHP and SFI-Parametric methods, the highest and lowest soil fertility indices were related to high and low productivity, respectively. The mean SFI- Fuzzy AHP of the high productivity tea were significantly higher than low productivity tea cultivation. It was found that SFI- Fuzzy AHP is superior to SFI-Parametric to evaluation of soil fertility for tea production .So that, the correlations between crop yields and SFI- Fuzzy AHP (R2= 0.63) is higher than SFI-Parametric (R2= 0.50).Conclusion Understanding the soil fertility status is one of the important aspects of sustainable soil management in order to optimal crop production and prevent environmental degradation. Considering the importance of yield as an important indicator in the sustainable management of agricultural ecosystems, it is expected that there is great potential for increasing crop yield by improving soil fertility. The SFI- Fuzzy AHP of the high productivity tea were significantly higher than low productivity tea cultivation and created more differentiation between various soil fertility classes in tea cultivation. Therefore, determining the soil fertility index by Fuzzy-AHP method to evaluate the soil fertility of tea cultivation is superior to the parametric method. Based on the obtained results, it is suggested that for the optimal tea production, in addition to the application of potassium fertilizer, the exact amount of which should be estimated based on the soil test results, the organic matter application should also be considered.