عنوان مقاله [English]
Climate change is an undeniable fact, and today this phenomenon has become a global issue. Its effects on crops yield and their stability facing increasing global climate change. Yield stability will be the most serious challenge for maintaining agricultural production and food security. After the cereals, pulses are the second most important source of food in Iran and the world, have great importance in agricultural systems and human nutrition. The yield of pulses has more variation than other crops, so the study of the yield stability of these crops can help the policy makers to develop the plans helping preservation and enhancement of pulses yield. The aim of this study was to research the yield stability of pulse crops in Iran for 33 years using different analytical methods.
Materials and Methods
All available statistics including the yield data on of chickpea, beans, and lentil data for the years 1983 to 2016, were collected from the published statistics by the Iranian ministry of agriculture. The residuals of regression between yield and time of the yields and its trends calculated from linear, bi-lines and tri‑lines models which were selected based on the higher coefficient of determination (R2) and normality of the residuals. Absolute values of the regression residuals were also used to calculate relative residuals of yields. The coefficient of variation (CV) for yields of every 4-year period was calculated by dividing the standard deviation by average. Mean yield of all pulses also were calculated as “Environment Index” to use in Finley-Wilkinson model. The positive slope of the residuals of linear regression, CV and Finlay‑Wilkinson model means the increase of yield instability and slope of zero and the negative slope of the linear regression indicates relative stability and increase of stability of the yield, respectively.
Results and Discussion
The increase in rainfed chickpea yield over the studied period was low and close to 0.75 kg ha‑1 y‑1. The trend of rainfed lentil yield was negative with a slope of -0.61 kg ha-1 y‑1 and the highest amount of yield increasement belonged to rainfed and irrigated bean by 25.17 and 21 kg ha‑1 y‑1. All the trends of residuals of pulses were positive that means instability of pulses yields over the studied period. Irrigated chickpea and rainfed lentil showed the highest CV trends and rainfed bean have had the highest range of values of CV. A CV as a simple and widely used parameter can show the standard deviation of the yield over the different environments and years, so higher values and positive trend of CV means higher fluctuations of yield level and its lower stability. Yield stability of the rainfed bean was lower than others but the trend of yield stability of irrigated chickpea and rainfed lentil is more than other pulses. Based on Finley-Wilkinson model, the trend of stability of all pulses was low and negative. Yield stability of the irrigated and rainfed bean was the lowest. Although due to the fact that rainfall is the major factor affecting the rainfed yield, it is expected that the irrigated yields to be more stable than rainfed yields, in contrary to our expectations, based on the results and the slope of the regression of the model, the yield of irrigated chickpea and lentil were more unstable than rainfed yield. The cultivated area of rainfed chickpea and lentil and irrigated beans showed a positive trend during the study period and inversely, the cultivated area of irrigated chickpea and lentil and rainfed bean were decreased. Absolute residuals of the yield as the indicator of stability (which has an inverse relationship) as a function of cultivated area, increased in about all of the studied crops except irrigated chickpea and rainfed bean. Most stable crops in the larger cultivated area were irrigated chickpea and rainfed bean.
According to the results, the overall trends in the yield increasement of pulse crops in Iran are low. The trend of chickpea and lentil has been much lower than rainfed and irrigated bean. On the other hand, fluctuations in yield over the past decades are high and therefore the stability of the country's pulses is also low. In Iran, it seems essential to development of new integrated and effective policies for the supporting scientific researched in the order to introducing new varieties, reduction of yield gap of pulses crops and improvement of their yield stability, and also education in order to improve the management of the pulse crops agroecosystems, as well as mitigation of the effects of climate change.