S. Topcu

Spatial and Temporal Variability of Groundwater Nitrate Concentrations in Irrigated Mediterranean Agriculture

As nitrogen (N) fertilizer-use efficiency rarely exceeds 50% in most agricultural systems, the potential leaching of N to the groundwater, particularly under irrigated conditions, has economic, health, and environmental implications. Research in the Akarsu irrigation district in the Lower Seyhan Plain in southern Turkey sought to determine spatial and temporal variability of groundwater (GW) nitrate (NO3) concentrations in 2007–2008. Shallow groundwater observation wells 3 m deep were installed at different locations to represent the whole irrigation district. Groundwater samples were collected (February, April, July, October) and analyzed for ammonium (NH4) and NO3 concentrations. Because NH4 values were negligible, only NO3 data were processed to determine spatial and temporal variability and then used to develop regional NO3 maps using geographic information systems. Groundwater NO3 concentrations ranged between 0.17 and 55.96 mg L–1 during the 2 years, only exceeding the critical 50 mg L–1 concentration in 1% of the area sampled. The areal mean of NO3 concentration was greatest in February, indicating a potential N leaching of unused N from the early season with intensive rainfall, especially in wheat-growing areas. Groundwater NO3 concentrations decreased after February; however, during the peak irrigation season in July, NO3 was relatively low because of crop uptake during spring and summer. In about half the area, groundwater NO3 concentrations ranged between 20 and 50 mg L–1 and were thus marginal relative to the critical pollution level. As N fertilizer use will continue to increase, especially with the expanded irrigation that is now occurring in the Mediterranean region, regular monitoring of groundwater NO3 is advisable under such conditions.

Water for Agriculture: A Major and Inefficient Consumer

The history of irrigated agriculture in Turkey dates back to as early as 6000 BC. Throughout history, Anatolia, located on the crossroads of many civilizations, has played an important role as a trade bridge between western and eastern countries. From the beginning of the Turkish Republic the agricultural sector was crucial for the economic development of the country in terms of producing food and fibre, supplying raw material for industry, preventing migration from rural to urban areas, and creating employment. Because of the unreliable and erratic precipitation regime, Turkish agriculture depends heavily on irrigation, an exception being the Eastern Black Sea Region. Real advancements in irrigated agriculture in the country started therefore with the development of land and water resources projects 60 years ago. In 2008, irrigated areas covered about 5.3 million hectares, in 1950 it was only 0.15 million hectares.