بررسی تنوّع حبوبات در بوم‌نظام‌های زراعی ایران

Introduction
In recent years due to problems associated with intensive agricultural systems, the role of legumes in the sustainability of cropping systems has been accelerated (Draper, 2006). Currently, one of the challenges of energy intensive agricultural systems is monoculture, which is associated with low biological diversity (Carmine, 2007). Iran has been considered as the area with low agricultural diversity and dominance of few crops particularly cereals in the main cropping systems (Nassiri Mahallati et al., 2003). The most common index of plant diversity is the SHANNON index. In agroecosystems, a Shannon index of 3 is rare (Meng et al., 1999). Researchers evaluated agrobiodiversity of agricultural systems at species, variety and cropping systems in a comprehensive survey for Iran and they found that the diversity at all levels have been declining due to introduction of new agricultural technology (Koocheki et al., 2005). They found that for wheat and rice which are the main cereal crops with high variety richness the SHANNON index ranges from 1.5 to 1.7. The aim of present study was to evaluate biodiversity of pulse crops in Iran and the future trends of yield, acreage and production.
Materials and Methods
In this survey, the status of pulse crops in different provinces of the country from 1983 to 2003 was evaluated. These crops were bean (Phaseolus vulgaris), chickpea (Cicer arietinum) and lentil (Lense culinaris). Other species of this category were classified as other pulse crops. The SHANNON index (H) was calculated based on the cultivated area (Smale et al., 2003):
For evaluating of the trends in biodiversity, cultivated area, production and yield, time series were used by the following formula:
Yt = f (t) + et (1)
Where, Yt is the variable at the time of t, f(t) is a function which describes Y on the bases of time and et is the prediction error of the time of t. Prediction of trend was calculated by direct method (Patchet, 1982) and the first year of data was considered as starting point. In this study, based on the type of time series, double dynamic mean and WINTERS method were used for the future prediction. In the WINTERS method, prediction is made on the bases of harmonized mean from time series data, in such a way that the highest weight is given to the nearest data and the weight of data is decreased with aversions from the present time.
Results and Discussion
The diversity index under rainfed condition showed an increasing trend whereas the reverse is true for the diversity index under irrigated condition. The diversity index for the whole pulse crops (rainfed plus irrigated) was inconsistent, but an increasing trend was observed from 1983 to 2003 and a decreasing trend was observed afterwards. The decreasing trend was also true for the prediction towards the year 2021. Similar trend as for the period 1983 to 2003 is expected up to the year 2021.
The acreage and yield for irrigated has been increased for bean, whereas for chickpea, the rainfed acreage has been increased. The lentil was similar to chickpea. The acreage of the other pulse crops showed a slightly increasing trend from 1983 to 2003. This rise is due, in part, to an increase in the irrigated acreage. This trend is likely to increase slightly over the coming years and is likely it will show a consistent trend afterwards. The yield of other pulse crops decreased from 1983 to 2003. This reduction is due to a reduction under rainfed conditions. The yield of other pulse will decreased until 2021.
The same trend is shown for production. Although production of bean has shown an increase, this increase is mainly due to an increase under irrigated condition, whereas the rise in lentil and chickpea is due to rainfed production. The same trend is expected up to the year 2021 for these crops. The production of the other pulse crops showed a slight decreasing trend from 1983 to 2003. This decreasing is due to a decreasing under irrigated and rainfed conditions. The trend will show increase for a few time and it will show a consistent trend afterwards.
Only the yield for bean has an increasing trend and this is associated with this fact that bean has been under irrigated conditions. No increase is shown for other crops which are produced under rainfed condition. Therefore, it may be concluded that the production increase for bean is mainly due to yield and acreage increase, whereas for other pulse crops, the production increase is due to increasing in the acreage, because the yield showed somewhat the decreasing trend during these years. Prediction of diversity index of rainfed pulse crops up to the year 2021 indicates an increase of 1.22 folds compared to the year 2003. However diversity index for irrigated and irrigated plus rainfed showed a reduction of 0.88 and 0.9 folds, respectively. The magnitude of the change of production, yield and acreage for different pulse crops is shown. It is apparent that the prediction of production for the bean up to the year 2021, under rainfed, irrigated and rainfed plus irrigated will be increased by 2.96, 1.60 and 1.95 folds compared with the year 2003. These values for the yield of bean under similar conditions are 1.59, 1.03 and 1.22 folds, respectively and also for the acreage will be 1.88, 1.58 and 1.59 folds, respectively.
Acreage for the chickpea and lentil for rainfed, irrigated and irrigated plus rainfed will be 2.47, 0.37, 2.41 and 2.63, 1.31, 2.54 folds, respectively. These values for other pulse crops will be 4.96, 1.49 and 2.01 folds, respectively. An increasing trend of the yield has been reported for the future for different crops (Khush, 1999; Rosegrant et al., 2001). Borlog (2000) has stated that yield growth which is associated with genetic improvement and the use of chemical fertilizers, pesticides and irrigation systems, will be continued, in the future.
We can predict that the rate of acreage and production of pulse crops in Iran, specially three important crops, bean, chickpea and lentil will increase until 2021. However, under rainfed conditions, it is likely that the yields, particularly of chickpea and lentil will stabilize.
Conclusions
This study was conducted to evaluate the trends in biodiversity, cultivated area, production and yield of pulse crops in different provinces of Iran from 1983 to 2003. Time series formula was used for such evaluation. The diversity indices studied under irrigated and rainfed conditions. It seems the results can be useful for policy makers, scientists and food industry to improve food security in country.