Economic evaluation of tillage systems on wheat grain yield under different water stress levels

Introduction
Conservation agriculture has positive effects such as reduced production costs, reduced water and input consumption, and positive environmental impacts, but its acceptance by farmers depends on their belief in the positive effects of this innovation and its alignment with their needs. This belief will be reinforced by increasing the economic efficiency of this system on farms. Benefits and costs of the adoption of conservation practices have been evaluated by a number of researchers.
Materials and Methods
The field experiment was designed as split plot arrangement in randomized complete block design with three replications with wheat- soybean rotation and conducted during 2017-2020 growing seasons at Zarghan research station of Fars province, Iran. Experimental treatments included; three tillage practices (conventional tillage (CT), reduced tillage (RT), and no-tillage (NT)), which were assigned to main plots and water stress levels included irrigation cutting at pollination, milky and seed dough developmental stages along with full irrigation in subplots. Profitability indexes (Income, Gross margin, Benefit-cost ratio, Sale return percent), and technique for order preference by similarity to ideal solution (TOPSIS) methods were used to select the best treatment. The difference between treatments income and cost compared to control treatment has been calculated and compared by profitability indexes. The differences in the treatment's benefits are due to the different wheat grain yields. In TOPSIS method, characteristics including water cost, weed control cost, production cost, grain yield and gross margin were considered to prioritize treatment(s), according to researchers’ views. Selected criteria were ranked based on mean of scores that allocated by researchers. The first step was decision matrix in which the rows and columns describe criteria and alternatives. Frequently, criteria were not the same in importance for decision makers. Therefore, weighted criteria should be considered by Analytic Hierarchy Process (AHP) method. Decision matrix contained a combination of data in various scales. Therefore, the normalized decision matrix by transformed various attributes dimensions to non-dimensional attributes. The second step was to multiply each column of the matrix by corresponding criterion's weight. The third and fourth steps were to identify ideal and negative ideal solutions and to calculate separation measures for each from them. The last step was to calculate relative closeness to the ideal solution and alternatives were appropriately ranked.
Results and Discussion

Results of profitability indexes showed that conventional tillage system was the first preference of treatments followed by reduced, and no-tillage systems, respectively.
Non-shared production costs under no-tillage system were higher than reduced (12.5 %) and conventional (10. 2 %) tillage systems, because of increasing irrigation, weed control, and fertilizer costs.
In the conventional and reduced tillage systems, full irrigation treatment had the highest gross margin that followed by cutting irrigation at seed dough developmental stage. Also, cutting irrigation at seed dough developmental stage under no tillage system had high gross marine by 113000 Rials per hectare.
The pair wise comparison indicated that the effective criteria to prioritize the best treatments were gross margin (0.250).
Based on relative closeness to the ideal criteria, the first and second preference of treatments were irrigation cutting at seed dough developmental stage (0.84) and full irrigation (0.80) under CT, respectively, which followed by irrigation cutting at seed dough developmental stage (0.78) and full irrigation under RT (0.75) systems during three years.
The highest wheat grain yield was obtained in full irrigation under CT and RT systems which were not significantly different from cutting irrigation at seed dough developmental stage under conventional, reduced, and no-tillage systems. The irrigation can be stopped at the end of grain filling without significant reduction in wheat grain yield under water limitation.
The highest gross margin was achieved in conventional tillage system; therefore, this system had a priority for farmers. The majority of farmers not pay the actual irrigation water cost. If the water price is included in economic evaluation, the production costs will be reduced under conservation tillage comparison to conventional tillage systems.
Application of TOPSIS method for decision making in agricultural experiments provides accurate and reasonable decisions.

 
Conclusion
Profitability indexes and multi-criteria-decision making methods were used for ranking treatments according to difference between treatments income and cost, the relative closeness to ideal criteria and maximum distance from negative ideal criteria. Results showed prioritizing the best treatments (water stress under tillage systems) were cutting irrigation, at seed dough developmental stage under CT and RT systems. Therefore, under water limited condition, stopping irrigation at the end of grain filling dose not significantly reduce wheat grain yield.
 
Acknowledgment
 The authors would like to express their deep gratitude to Fars Agricultural and Natural Resources Research and Education Center and Department of Plant Production and Genetics, School of Agriculture, Shiraz University for all support including finance, academics, and facilities for this research work. We are also very grateful to Dr. Hormoz Asadi, who collaborated and shared ideas to preparing the article.