s:1534:"%T Fertilizer nitrogen movement in central Amazon oxisol and entisol cropped to corn 
%A Melgar R J 
%A Smyth T J 
%A Sanchez P A J 
%A Cravo M S 
%X Nitrogen fertilization experiments were conducted on a Oxisol and Entisol in the Central Amazon to evaluate the influence of soil properties and rainfall distribution on soil inorganic N movement and N recovery by corn (Zea mays L.). One corn crop was grown during the wet season on each site. A second crop was planted in the Oxisol during the dry season. Inorganic N was monitored in urea-N treatments (0 to 160 kg ha1) to a depth of 0.60 m by periodic soil sampling during each crop. During the wet season large N losses by leaching occurred in both soils with 120 or 160 kg ha1 of applied N. Differences in soil permeability and corn rooting depth between soils contributed to a greater movement of N into subsoil layers in the Oxisol than the Entisol. However, N leaching beyond 0.60 m in the Oxisol was delayed, apparently because of NO3 adsorption in the net positively charged subsoil layers. Corn yields and N recovery in the Entisol were higher than in the Oxisol, during the wet season. During the dry season N leaching in the Oxisol was greatly reduced, relative to the previous wet season, by split applications of fertilizer N and lower cumulative rainfall (300 vs. 1012 mm). Management practices which promote root growth into acid subsoil layers of the Oxisol would increase plant access to soil N, improve crop N recovery and reduce fertilizer N requirements. 
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