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The Application Of Fertilizer Using Management Zone (MZ) In Pampas Soils With Texture Variability Affects Residual Nitrate After Harvest
1M. Rodriguez, 2G. Civeira, 3S. Urricariet, 3P. Muschietti, 3R. Lavado
1. School of Agronomy, Buenos Aires University
2. Buenos Aires University
3. Buenos Aires Univsersity

          The maize yields are usually associated with soil texture heterogeneity in western Argentinean Pampas.  In this area, the uniform fertilizer management (UM) increased the risk of nitrate leaching due to over-fertilizing but it could be minimized by using different management zones criteria (MZ). In a field experiment, the nitrates distribution in soil depth (0-1.80 m) at sowing and harvest times (residual Nitrate) and the maize response to N fertilizer were determined. The experimental area was divided into UM and MZ fields. The MZ fields were arranged by texture and organic matter content and were split into subfields as  high production zones ( HP )(coarse silty loam texture) and low production zones ( LP ) (coarse loam texture). Both MZ and UM received 2 treatments with three replications each: unfertilized (control) and fertilized (N rate calculated according to N balance). The maize yields varied from 7959 to 11102 kg ha-1 and from 7466 to 9722 kg ha-1 for HP and LP respectively. Residual Nitrate also varied between zones in the 0-1 m soil depth. Residual Nitrate level in the LP fertilized zone was similar to control and lower than UM while in the HP fertilized zone, the residual Nitrate level was two times higher than the control and the UM probably due to the excessive N rate (240 kg N ha-1). Nevertheless, in the 1 – 1.8 layer depths the Nitrate content in both zones did not vary when compared to control and UM. This fact indicates that the residual Nitrate in HP remained in the upper layer during the maize but represents risk of nitrate leaching in future. These results indicates that the fertilization by using MZ can minimized the residual Nitrate as compare to the UM if N is applied in its optimum rate, especially when high yields are expected. 

 
Keyword: Management zones criteria, maize, Residual Nitrates, Nitrogen fertilization