Implications of Profile Mineral Nitrogen in an Irrigated Project Area of Southern Turkey

Abstract

With intensification of agricultural production based on irrigation, management of required inputs such as nitrogen (N) is vital from economic and environmental standpoints. Ideally, the applied N has to be most efficiently used by the crop, and loss of N from cropped land has to be eliminated or minimized to avoid water pollution. As both nitrate (NO3) and ammonium (NH4) in the soil profile are plant available, it is termed mineral N (Nmin, NO3-N + NH4-N), and has to be considered in making fertilizer recommendations. Despite the development of irrigation schemes in Turkey and the associated intensity of cropping, there is little rational basis for N fertilizer application rates. Thus, in the Akarsu Irrigation District (9,495 ha) in the Seyhan Plain of southern Turkey, we sampled soils with profile depth of 0-90 cm at points adjacent to 107 drainage observation wells, once in 2009 and again in 2010, and analyzed the samples for NO3 and NH4. Maps were prepared based on inverse-distance-weighted interpolation. In the surface horizon, NO3-N concentrations were 82.8 and 57.8 mg kg(-1) compared to the ammonium values of 3.1 and 2.6 mg kg(-1)in consecutive two years. Although NO3 was considerably greater than NH4 in all cases, both forms decreased with depth. Though this broad survey established some high levels of N in the soil (110 and 106.6 kg Nmin ha(-1)in 2009 and 2010), which would require applying less fertilizer N, there was no evident relationship with soil or cropping practices, which would require detailed N-budget analysis for each field or crop. For effective management of such irrigation schemes to reduce N loads in drainage waters, soil N is only part of a strategy that includes N in groundwater, soil and water salinity, and effective drainage.