Introduction

It is difficult to measure sustainable agriculture as a multidimensional concept. While it is relatively easy to express philosophical definitions of agriculture sustainability, providing an operational and methodology definition for evaluating the level of sustainability is difficult. Different methodological approaches have been formulated and developed to assess the sustainability levels of sustainable agriculture. However, there is no consensus on a comprehensive framework for identifying and selecting indicators, different scales of indicators, weighting and especially for aggregating individual indicators into a final composite indicator and rating of sustainability level. So, Evaluation of sustainable agriculture is an important challenge for agriculture researchers, agents, and policymakers. A comprehensive approach for stability analysis is the complexity of each other-need activities. That's why we need a comprehensive analytical framework for evaluating sustainable agriculture development and use. This study presents a certain methodological approach to evaluate and determine the sustainability of agricultural production at farm-scale which integrates all the individual indicators of ecological, economic and social stability into a comprehensive final index. In a case study, in order to test the proposed methodology, 22 individual indicators were selected. Then, a local condition of rice cultivation in Sari County was studied through an open review of 287 rice farmers.

Methodology

Agricultural sustainability can be evaluated at different spatial scales including field, regional, national and even international measures. However, due to the specific conditions of each region, its natural environment, socio-economic conditions and agricultural techniques, necessity of a transparent scale is unavoidable. Most national indicators are not applicable at the scale of individual farms which are the purpose of the intended operations. In this study, 22 single index fields were selected to demonstrate and test the proposed methodology in a specific case study. Then, its relevance to the local conditions of rice cultivation in Sari County was studied by examining 287 rice farmers. Considering relative importance and impact of social, economic and ecological factors on the total sustainability, a methodology of Analytical Hierarchy Process (AHP) was applied by exploring the views of experts to determine the weight. Finally, the final composite indicator of sustainability was created through the integration of the three components of sustainability. A questionnaire was designed to collect data for the current farming operations. It consisted of three parts, namely: a) agricultural land management practices; b) economic performance and c) social characteristics of each farm. The questionnaire was designed in such a way to be completed in the shortest possible time. Thus, it was consisted of useful sections for measuring and providing information related to the entire system of agricultural production.

Discussion and conclusion

The results of this study indicate that 17.77% and 53.66% of rice production system is unstable and potentially unstable. While the sustainability level of social component was standing in a satisfactory situation, the sustainability level of economic and ecological components was still changing. In addition, farm sustainability was higher for those farmers using the method of biological control, low-product seed, agro-ecological management practices, owners of integrated land and participants in training and extension courses. The level of education, family labor, and the amount of self-consumption of rice are factors of positive and direct relations with ecological sustainability. On the other hand, the amount of rice production causes significant negative effects on it. Age, farming experience, level of education and the amount of self-consumption show a positive significant relation with social sustainability. In addition, education, land size, selfconsumption, the amount of produced rice and productivity index are in a significant positive relation with economic sustainability. In general, factors including education, extension communication, attending training courses and the information source of consumption play a key role in the increasing of farmers' awareness. In this study, to evaluate and compare the sustainability of agricultural production system in farm scale, a methodology framework has been provided by the combination of three components of sustainability, i.e. economic, social and environmental. However, it cannot be claimed that the proposed methodology is quite authentic to evaluate the complicated phenomenon of sustainability. Different facilitating assumptions are required for the use of this methodology. Of course, it has several advantages and also can be used for different purposes. Thus, the following hints are noteworthy in the methodology section:

- Variables and indicators of sustainability should be selected according to the specific circumstances and context of each area and the topic at hand, as well.

- Validation and preliminary test of indicators is ensuring their appropriateness and being measurable in the current conditions of any region.

- Weight allocation model based on the views of experts and AHP, can obviously show the importance of individual indicators in the final integrated one.

- The integration of the three components of sustainability into the final one should be due to the relative weight of the components.

- In the process of making indicators, positive and negative effects of indicators on the overall sustainability must be considered.