Abstract
This study investigated whether continuous and combined application of fresh crop residues and inorganic N fertilizer
could improve N use efficiency in irrigated drylands. N recovery from inorganic fertilizer in the crop/soil systems was
studied in the field for six seasons (August 2006 to February 2009) of guar (Cyamopsis tetragonoloba)-wheat (Triticum
aestivum L.) crop rotation using 10 atom% excess 15N enriched urea (12.72 kg ha–1). Results showed that after one season, 31-34% of the applied 15N was recovered in the above ground plant part of which, 42% was recovered in the straw (leaves 33% and stems 9%). Across all seasons, average total N recovery in the plant (25%) and total soil (0-60 cm) N recovery (47%) in crop residue plots were 11 and 4%, respectively higher than that found in corresponding residue removal plots (23, 45%), respectively. After harvest of the 1st crop and before incorporation of crop residues, N unaccounted for ranged between 10 and 17% whereas during five seasons of successive application of crop residues, N unaccounted for in crop residue plots was 23-61% compared to 27-63% in residue removal plots. The proportion of total plant N derived from the atmosphere via the process of N2 fixation (%Ndfa) had ranged from to 38 to 65% (34-54 kg ha-1). These results indicate that continuous application of crop residues along with fertilizers improved N use efficiency and decrease losses.
