Abstract
Technical and scale efficiencies have been widely studied in agricultural production literature, but many of the inputs used can impact the environment. Environmental impacts can take the form of undesirable output, a non-discretionary production input or, as has been the case in many studies, a conventional input. In this paper, we develop a DEA (Data Envelopment Analysis) model with water salinity as a non-discretionary input and estimate a model of irrigation water demand function based on the role of water in the farm production function. We model production technology by distinguishing six inputs (water, labor, phosphate, farmyard manure, farm size and water salinity) and four outputs (date production, vegetable production, cereal production, and fruit production). The adjusted-DEA model is applied on a transversal data of 138 water users associations farms.
On average, the technical efficiency for our sample observations is 0.63, which means that, on average, the farms can produce the same level of outputs with only sixty three per cent of the inputs if they are operating at the input frontier. Moreover, we also observe that there is wide variation in the measure of technical efficiency across farms. Spearman coefficient of rank correlation is used to test whether the farms' performance rankings, before and after accounting for water salinity, are significantly different. We find that accounting for variations in water salinity does not significantly bias the relative performance of the farms. The mean of scale efficiency levels is about 0.89. The results also show that 70% of farms are operating at below the optimal scale of production and 50% of oases farmers could improve SE (first mention, no full term) if they increased scale in terms of farm size.
The shadow prices of irrigation water derived from the adjusted-DEA model are positive, reflecting that water is a normal input in the production process. The estimation of a model of irrigation water demand function enables us to derive the shadow price elasticities of the inputs. It should be noted that the price elasticity of water is significant and quite high. Thus, the high responsiveness of water demand to price suggests that pricing policies can be a potential instrument for water conservation.
ملخص
يكمن الهدف الرئيسي من هذا البحث في تقدير إجراءات قياسات الكفاءة و التقنية ومرونة سعر مياه الري بالنسبة لمزارع الواحات في جنوب غرب تونس. يتم تقدير قياسات الكفاءة والتقنية غير المقيدة بتنوع ملوحة المياه من خلال تحديد ملوحة الماء باعتبارها عنصر إدخال غير تقديري في نموذج تحليل حافظة البيانات الموجه نحو البيانات المدرجة به. وتقدر قيمها بحوالي 63 % و 89 % على التوالي. ويسمح وتقدر مرونة سعر مياه الري ب – 0.44 . ويتضح أن هذه المرونة على قدر من الأهمية وبالتالي فإن القيام بتسعير المياه قد يشكل وسيلة هامة للقيام بإدارة الموارد المائية بشكل أفضل. وتشير النتائج الخاصة بمرونة الأسعار الصورية فيما يتعلق بمدخلات المزرعة غير المتعلقة بالمياه، مثل الأسمدة والعمالة، إلى أن هذه المدخلات مكملة للمياه
