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Download or read book Cation and Nitrate Leaching in an Oxisol of the Brazilian Amazon written by Michael David Cahn and published by . This book was released on 1991 with total page 416 pages. Available in PDF, EPUB and Kindle. Book excerpt: The general objetive of this research was to study how urea and legume green manures in a corn production sequence may influence nutrient leaching in a oxisol of the humid tropics, where subsoil acidity inhibits deep rooting. A 1.3 year split-plot field experiment was conducted on a clayeywxisol (Tipic Acrudox), near Manaus, Amazonas, Brazil to: 1) measure the leaching of NO3, Ca, Mg, and K and the acidification of an oxisol under cropping sequences utilizing urea and legume-green manure sources of N; and 2) measure the effects of soil acidification on maize and legume yields. Main plots received two levels of lime and a blanket application of K. Sub-plots were cropped with: 1) a legume green manure (Canavalia ensiformes or Mucuna aterrima) followed by maize; 2) maize receibing urea-N; or 3) left bare-fallow with an application of urea-N. Plots were periodically sampled to 1.2m and soil water was monitored with tensiometers. The experimental site received 4265mm of precipitation during 1.3 years; approximately 60% to 90% of this rain percolated through the profile. Applied N and K leached from the plow layer and a significant fraction accumulated in the subsoil during 120 days. Also, a significant portion of the nitrate leached beyond 1.2m during the experimental period. Nitrate was sorbed onto the solid phase: sorption increased with depth and it had an important influence on the rate of leaching of N03- and cations. Calcium and magnesium leached from the plow layer; some accumulated in the subsoil, and some was lost from the soil profile. Acidity increased in the plow layer of unlimed plots during the experimental period. Plots cropped with canavalia were least acid, and plots receiving urea were most acid. Soil acidification during the experimental period influence crop yields: 1) grain yields of unlimed plosts, receiving urea, decreased by about 50% between the first and third maize crops; 2) the effect of lime on the weight of legume dry matter increased with time. Cation leaching reduced subsoil acidity, but not sufficiently for roots to penetrate deeply. Because 90% of maize roots were distributed in the 0cm-30cm horizon, moisture stress reduced grain yields of the second maize crop, though water was available in the subsoil.