Abstract

Nitrogen deficiency ranks right behind water as the second most constraint to crop production in the coarse - loamy sand of the Gareh Bygone Plain (GBP) in southern Iran. As better resource utilization is essential to wise energy management, contrary to the reported cases, surface water pollution by N maybe a boon in the GBP. The Agha Jari Formation, in which the Bisheh Zard Basin (BZB) that supplies the GBP with floodwater has been formed, contains NO-3 and NH+4 in its sandstone, siltstone and marl components. Therefore, it is expected that some of the geologic N dissolved in floodwater, and carried by the suspended load, reach the watertable, and also supply the plants coming in contact with the water and/or sediment.

To study the origin of N in the BZB, and investigate the fate of the dissolved and adsorbed N as it travels form the watershed to the watertable, 13 rock samples, 7 floodwater samples and 71 soil samples were collected and analyzed for NO-3and NH+4. The NO-3concentration was higher than that ofNH+4 in all of the samples: 77 ppm vs. 38 ppm in the floodwater; 47 ppm vs. 20 ppm in the soil; and 22 ppm vs. 12 ppm in the rocks. Assuming the mean annual inflow of the GBP floodwater spreading system in 10 million m³, the system receives 370 metric tons of NH+4 and 770 metric tons of NO-3 which exceed the N requirement of the small grains if this system is planted to them.