Abstract: The incredibly low yield for crops grown on irrigated calcareous soils in Afghanistan could be attributed to fertility problems related to the shortage of available phosphorus (P). The objective was to investigate P for soils representing irrigated cropland in Afghanistan. A total of 14 soil pedons were sampled from Farah and Kunar provinces. A total of 42 soil samples were selected from the top three horizons in these pedons. The Natural Resources Conservation Service double-point anion exchange resin (DP-AER) extraction method was applied to investigate P availability, capacity, and release characteristics in these soils. The data obtained from the DP-AER method were compared with available P determined by the Olsen, Mehlich-3, and water methods. The amount of readily available P measured by the methods followed this order: water < Olsen < DP-AER < Mehlich-3 and averaged 0.14, 4.95, 9.73, and 15.2 mg/kg soil, respectively. The P capacity ranged from 1.21 to 87.3 mg/kg, with an average of 22.3 mg/kg soil. After a fast release of the readily available forms, the rate of P release from soils slowly decreased with time, indicating a dissolution process from sparingly soluble phosphate minerals. The amount of available P, capacity, and release rate were generally low for most soils. Phosphorus fertilizers and organic amendments should be recommended to improve soil fertility and secure good harvest for the irrigated cropland in Afghanistan. Either the Olsen or the DP-AER method could provide a good index for P availability in these soils. However, the DP-AER method could also supply useful information on both the soil P capacity and release characteristics.
U.S. Department of Agriculture, National Resources Conservation Service, National Soil Survey Center, Lincoln, Nebraska, USA.
Address for correspondence: Dr. Moustafa A. Elrashidi, 100 Centennial Mall North, Lincoln, NE 68508, USA. E-mail: firstname.lastname@example.org
Received September 21, 2011.
Accepted for publication December 8, 2011.
Financial Disclosures/Conflicts of Interest: None reported.