SOME NITROGEN FERTILIZER SOURCES AND SPLITTING EFFECT IN THE PRESENCE AND ABSENCE OF ORGANIC MANURE ON COTTON YIELD AND AVAILABLE SOIL NITROGEN

two field experiments were conducted at the experimental farm of  Sakha Agricultural Research Station during 2007 and 2008 summer seasons to study the effect of splitting some nitrogen fertilizers (ammonium nitrate and urea) in two or three doses with or without organic manure on cotton yield (Gossypium barabadense, varity Giza 86), soil available nitrogen and NO₃-N.
The results can be summarized as follows:-

Cotton yield was scientificantly higher with organic manure by 23% and 22% in the first and second seasons, respectively.
Ammonium nitrate application with organic manure resulted in higher cotton yield than urea. While the opposite results were obtained in the absence of organic manure.
The fertilizer splitting into two doses had significant increase in cotton yield regardless the type of N- source.
The highest cotton yield (10.25 kentar/ fed.  ) was obtained by application of ammonium nitrate fertilizer in two doses and with organic manure
Available nitrogen was increased by 53.4% with organic manure application. Significant increase was noticed in soil available nitrogen with application of ammonium nitrate than urea fertilizer. The calculated relative increase was 20.7%.  the two doses application of n- fertilizer gave high significant increase of available nitrogen than the three doses application (12.6%).
With application of ammonium nitrate fertilizer, available nitrogen was increased gradually by going deeper to reach 80 cm, these calculated increases were 27.5, 29.7 and 39.5 % of that at the top layer after 45, 60, and 75 days from sowing. While with application of urea fertilizer, available nitrogen was decreased gradually with deeper layer. The calculated relative decreases at deeper layer (40-80) were 18.3, 21.6 and 21.2% of that at top layer (0- 20 cm) after 45, 60 and 75 days from sowing.
Amounts of NO₃- N were always higher in the presence than in absence of organic manure. the calculated relative increase was 56.7%.
Application of ammonium nitrate or urea fertilizer led to nitrate accumulation at deeper soil layer, but application of ammonium nitrate caused a marked high nitrate accumulation compared to urea (63.1%).
Application of nitrogen fertilizer in two doses was found to increase NO₃-N in the soil profile by 13.3% than that of the three doses.