Cation and Nitrate Leaching in an Oxisol of the Brazilian Amazon

Abstract

High rates of N'fertilizers are often nec<ssz -0 ach:eve yield goals in the humid tropics, where subsoil acidity prevents deep crop rooting. However, leaching of fertilizer nitrate may accelerate the leaching of bases from the crop rooting zone, leading tb an acidification of the topsoil and a reduction in crop yields. Our ojective was to investigate the influence of urea and legume green manure sources of N on crop yields, leaching of cations, and the fertility of the plow layer of a clayey Oxisol (Typic Acrudox) of the central Amazon basin. We established a split-plot field experiment near Manaus, Brazil where main plots received 2 levels of lime (0 and 4 MVha CaCO,) and sub-plots were cropped with (i) a legume green manure (Canuvalio emiJonnes L. or Mucuna atemmma L.) followed by maize (Za mays L.); (ii) maize receiving 300 kg ha-' of urea-N, or (iii) leff bare-fallow with an application of 300 kg ha-' of urea-N. Plots were periodically sampled to 1.2 m during three cropping seasons. The field site received 4265 mm of rain during the experiment (16 mo). Legume crops accumulated between 142 and 280 kg ha-I of N. The distribution of NO, in the soil profile changed in a pattern consistent with leaching. All treatments lost Ca and Mg from the plow layer during the experimental period. Losses were greatest (500-1000 kg ha-' for Ca and 50 kg ha-' for Mg) in plots treated with urea and lime. Leaching of bases and the generation of acidity decreased base saturation in the plow layer of all treatments, but was minimized in plots receiving legume green manure N, perhaps because less inorganic N was applied andlor the legume crops recycled leached bases. Unlimed plots receiving urea, had the highest increase in acidity in the 0 to 3O-cm layer and a corresponding 440/o reduction in grain yield between the first and third maize crops.

Nitrogen fertilizer leaching in an Oxisol cultivated with sugarcane

“…There are few studies about leaching in this condition and in 2007 in the State of São Paulo, 40% of the harvest took place without burning (Goldemberg et al, 2008). In other studies, despite the low N leaching losses, significant amounts of K, Ca and Mg should have leached, which may result in soil acidification (Cahn et al, 1993;Ghiberto et al, 2009;Ng Kee Kwong and Deville, 1984;Oliveira et al, 2002). This is important if we consider that acidification is reversible by liming, but when it takes place in the subsoil, amelioration is much more difficult and expensive (Hartemink, 2008).…”

Maize yield and nutrition during 4 years after biochar application to a Colombian savanna oxisol

“…Calcium and Mg were applied as dolomite in 2002, and in small amounts with fertilizer thereafter. These nutrients are prone to extensive leaching in Oxisols (Cahn et al 1993;Ernani et al 2006). Although Ca and Mg stocks declined after 2004, Ca and Mg loss over time was lower with biochar application.…”

Nitrate sorption in the profile of an acid soil

“…Soil used in the sorption study was composited from samples of a field, used for maize experiments over the last 6 years (Cahn, 1991), and located at the Centro de Pesquisa Agroflorestal de Amazonia, (CPAA) 30 km northeast of Manaus, Brazil. CPAA is the national research center for agroforestry of the Amazon and is operated by the Empresa Brasileira de Pesquisa Agropecuaria (EMBRAPA).…”

“…The soil is classified by U.S. soil taxonomy as a very fine kaolinitic, isohyperthermic Typic Acrudox (Melgar, 1989) or by Brazilian soil taxonomy, a yellow latosol. Average clay content of the soil is 80% (Melgar, 1989), average pH is 4.5, and effective cation exchange ranges between 1.0 and 3.0cmol kg -1 (Cahn, 1991).…”