Abstract
This study evaluated the effect of hairy vetch (Vicia villosa Roth) as cover crop on maize nutrition and yield under no tillage using isotope techniques. For this purpose, three experiments were carried out: 1) quantification of biological nitrogen fixation (BNF) in hairy vetch; 2) estimation of the N release rate from hairy vetch residues on the soil surface; 3) quantification of 15N recovery by maize from labeled hairy vetch under three rates of mineral N fertilization. This two-year field experiment was conducted on a sandy Acrisol (FAO soil classification) or Argissolo Vermelho distrófico arênico (Brazilian Soil Classification), at a mean annual temperature of 18 ºC and mean annual rainfall of 1686 mm. The experiment was arranged in a double split-plot factorial design with three replications. Two levels of hairy vetch residue (50 and 100 % of the aboveground biomass production) were distributed on the surface of the main plots (5 x 12 m). Maize in the sub-plots (5 x 4 m) was fertilized with three N rates (0, 60, and 120 kg ha-1 N), with urea as N source. The hairy vetch-derived N recovered by maize was evaluated in microplots (1.8 x 2.2 m). The BFN of hairy vetch was on average 72.4 %, which represents an annual input of 130 kg ha-1 of atmospheric N. The N release from hairy vetch residues was fast, with a release of about 90 % of total N within the first four weeks after cover crop management and soil residue application. The recovery of hairy vetch 15N by maize was low, with an average of 12.3 % at harvest. Although hairy vetch was not directly the main source of maize N nutrition, the crop yield reached 8.2 Mg ha-1, without mineral fertilization. There was an apparent synergism between hairy vetch residue application and the mineral N fertilization rate of 60 kg ha-1, confirming the benefits of the combination of organic and inorganic N sources for maize under no tillage.
Highlights
Cover crops are planted to enhance soil fertility and quality and to increase the yield of the following cash crop (Santi et al, 2003)
The potential of hairy vetch as maize N source is directly linked to the efficiency of biological nitrogen fixation (BNF), the biomass production and the decomposition pattern of the crop residue
BNF accounted for 66.6 78.2 % of the total N accumulated in hairy vetch biomass in 2003 and 2004, respectively, averaging 72.4 % in both years
Summary
Cover crops are planted to enhance soil fertility and quality and to increase the yield of the following cash crop (Santi et al, 2003). Cover crops represented one of the most traditional farming techniques. Until the first half of the 20th century, leguminous green manure was the main N source for grain crops (Reeves, 1994). After the Second World War there was a drastic shift due to the increased availability of mineral N obtained by the Haber-Bosch process. By this industrial process, nitrogen (N) from air and hydrogen (H) from water are combined under high pressure (35–100 MPa) and temperature (300–400 oC), resulting in ammonia and other compounds such as urea. The energetic cost of the Haber-Bosch process is high, with a demand of about 1.3 Mg of fossil fuel to produce 1 Mg of N (Marin et al, 2009)
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