Nitrogen retention and plant uptake on a highly weathered central Amazonian Ferralsol amended with compost and charcoal
Christoph Steiner, Bruno Glaser, Wenceslau Geraldes Teixeira, Johannes Lehmann, Winfried E.H. Blum, and Wolfgang Zech. 2008. Nitrogen retention and plant uptake on a highly weathered central Amazonian Ferralsol amended with compost and charcoal. J. Plant Nutr. Soil Sci. 2008.
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Abstract:
Leaching losses of N are a major limitation of crop production on permeable soils and under heavy rainfalls as in the humid tropics. We established a field trial in the central Amazon (near Manaus, Brazil) in order to study the influence of charcoal and compost on the retention of N. Fifteen months after organic-matter admixing (0–0.1 m soil depth), we added 15N-labeled (NH4)2SO4 (27.5 kg N ha–1 at 10 atom% excess). The tracer was measured in top soil (0–0.1 m) and plant samples taken at two successive sorghum (Sorghum bicolor L. Moench) harvests.
The N recovery in biomass was significantly higher when the soil contained compost (14.7% of applied N) in comparison to only mineral-fertilized plots (5.7%) due to significantly higher crop production during the first growth period. After the second harvest, the retention in soil was significantly higher in the charcoal-amended plots (15.6%) in comparison to only mineral-fertilized plots (9.7%) due to higher retention in soil. The total N recovery in soil, crop residues, and grains was significantly (p < 0.05) higher on compost (16.5%), charcoal (18.1%), and charcoal-plus-compost treatments (17.4%) in comparison to only mineral-fertilized plots (10.9%). Organic amendments increased the retention of applied fertilizer N. One process in this retention was found to be the recycling of N taken up by the crop. The relevance of immobilization, reduced N leaching, and gaseous losses as well as other potential processes for increasing N retention should be unraveled in future studies.
Introduction:
The fertility of highly weathered Ferralsols in the tropics is low, and soil organic matter (SOM) plays a major role in sustaining soil productivity. Thus, long-term intensive use is not sustainable without nutrient inputs where SOM stocks are depleted (Tiessen et al., 1994). Due to low nutrient-retention capacity and high permeability of these soils, strong tropical rainfalls cause rapid leaching of mobile nutrients such as those applied with mineral N fertilizers (Hölscher et al., 1997a; Giardina et al., 2000; Renck and Lehmann, 2004). …
Only relatively small amounts of charcoal are produced by the traditional slash-and-burn technique. Charcoal represents only 1.7% of the preburn biomass if a forest is converted into cattle pasture (Fearnside et al., 2001). Producing charcoal for soil amelioration from aboveground biomass instead of converting it to CO2 through burning might be an alternative to slash-and-burn (Lehmann et al., 2002; Steiner et al., 2004b; Lehmann et al., 2006).
The existence of so-called “Terra Preta de Índio” (Indian black earth) suggests that a human-induced accumulation of SOM can be maintained over centuries (Sombroek et al., 1993). These soils are exceptionally fertile, and their productivity is most likely linked to an anthropogenic accumulation of P and Ca associated with bone apatite (Lima et al., 2002) and black C (BC) as charcoal (Glaser et al., 2001).
