Relevance of Wheat Yield Gap Concept in Tunisia.

Cereals occupy most of the area planted to field crops in Tunisia. Between 1.2 and 1.5 million hectares are sown to cereals; wheat accounts for 70 to 80 % of cereal production, the rest being barley and oats. Durum wheat occupies three quarters of the wheat area. Out of 4.45 million hectares of arable land, less than 3% is irrigated. The wheat is almost entirely grown under rainfed conditions. Increasing wheat production will be one of the greatest challenges facing Tunisian government today. Two main options could be considered (i) expand wheat planting areas at the expense of other land uses, or (ii) increase the yields (per unit area) of existing wheat lands. Under current conditions, the last option is more viable.

The objective of this study is to assess wheat yield gap in Tunisia under rainfed and irrigated conditions in order to identify factors which are limiting wheat production at regional and national scales. The wheat yield gap is defined as the difference between yield potential and the average yield of farmer fields. We followed the methodology and protocols developed by the Global Yield Gap Atlas (http://yieldgap.org/). Different wheat buffer zones were identified based to delimitation of climatic zones and wheat area distribution. The WOFOST model was used to estimate wheat yield potential based on 10 years (2003-2013) of daily weather data.

A large variation of average yield was observed among regions, ranging from 0.3 to 2.1 t.ha^-1 under rainfed conditions and 0.8 to 3.1 t.ha^-1 under irrigated conditions. The wheat yield gap is about 2.8 t.ha^-1 and 3.2 t.ha^-1 under water and no-water limited conditions respectively. This result could be explained by a weak WUE in irrigated systems.