Impact of Nitrogen Fertilization on Soil Organic Carbon Decomposition

Mostafa Y. Khalafalla and Mahdy H. Hamed

A field study was conducted at The Experimental Farm, Fac. of Agric., Al-Azahar University, Assuit, located 375 km south of Cairo, Egypt (27° 12- 16.67= N latitude and 31° 09- 36.86= E longitude) through wheat growing season 2015. The aim of current study is to asses the effect of nitrogen fertilizer types (urea and ureaform) at different levels on soil organic carbon decomposition. Soil organic carbon decomposition percentage (SOCD) is at a minimum amount in the 2nd week and at a maximum amount in the 7th week at the recommended urea level - 15% (R-15%). The biweekly SOCD % varied from 0.82 and 9.55 % at 70 kg N/fed level (R-30%). SOCD% ranged between 0.16- 12.73, 5.14- 10.61 and 0.41- 8.78% for ureaform level at (R-15%) and (R-30%) less than the recommended one (R), respectively. The amount of soil CO2 flux from recommended ureaform level treatment was the highest one during the entire growing season. Overall, SOCD% followed the order of R > R-15% > R-30%. The highest values of SOCD % were 8.4 and 8.2 at 2.4 Q10 value with urea and at 2.7 Q10 value with ureaform, respectively. The lowest values of SOCD % were 2.3 and 4.4 at 2.2 Q10 value with urea or ureaform, respectively. Soil C: N raties under all treatments were higher than that of initial state except that under R-30% of urea. The soil C: N ratio was higher at R-15% of urea than that when soil treated by ureaform. The opposite trend is true at R-30%.