The Agha Jari Formation: A Potential Source of Ammonium and Nitrate Nitrogen Fertilizers

Nitrogen deficiency ranks right behind water shortage as the second-most constraint to crop production in the coarse-loamy sand of the Gareh Bygone Plain (GBP) in southern Iran. Since better resource utilization is essential for wise energy management, contrary to reported cases, surface water pollution by N maybe a boon in the GBP. The Agha Jari Formation (AJF), in which the Bisheh Zard Basin (BZB) has been formed, contains an-omalously high concentrations of NO۳ and NH۴+ in its calcareous sandstone, siltstone and marl components. As about ۶۰% of our irrigation water is supplied through under-ground resources and are heavily over-exploited, the artificial recharge of groundwater (ARG) is actively pursued in Iran. Therefore, a major proportion of the ephemeral dis-charge of the BZB is spread over ۱۳۶۵ hectares of sedimentation basins and recharge ponds of the ARG system in the GBP. These basins and ponds are covered with improved rangeland, and eucalyptus (Eucalyptus spp.) and acacia (Acacia spp.) plantations. There-fore, it is expected that some of the geological-N dissolved in floodwater, and also carried by the suspended load, will reach the groundwater and supply the plants coming in con-tact with the water and/or sediment. Moreover, as both NO۳ and NH۴+ are considered pollutants of groundwater, the relative abundance of each should be determined, so that possible remedial measures can be designed and implemented. To study the origin of N in the BZB, and to investigate the fate of the dissolved and adsorbed N as it travels from the watershed to the root zone, ۱۳ rock samples, ۵ floodwater samples and ۸۱ soil samples were collected and analyzed for NO۳and NH۴+. The NO۳-N concentration was lower than that of NH۴+-N in most of the samples: ۵.۱ vs. ۹.۶ mg kg-۱ in rocks, ۱۳.۴ vs.۱۷.۴ mg L-۱ dis-solved in floodwater, ۱.۳ vs.۴.۳ mg kg-۱ carried by the suspended load, and ۱۰.۶ vs.۱۵.۵ mg kg-۱ in the ۰-۱۲۵ cm soil profile. Assuming that the mean annual inflow of the GBP-ARG system is ۷ million m۳ ,we receive ۸۹.۴±۵۲.۴ kg ha-۱ yr-۱ of NH۴+-N and ۶۸.۷± ۲۴.۶ kg ha-۱ yr-۱ of NO۳-N, of which some furnishes the vegetative cover with N. A part of what remains may reach the watertable after passing through the vadose zone.

کلیدواژه ها:

AJF ، Agha Jari Formation ، ARG ، Artificial recharge of groundwater ، BZB ، Bisheh Zard Basin ، GBP ، Gareh Bygone Plain ، MRT ، Multiple Range Test