Abstract

CENTURION, Gastón et al. Green-bridge-crops residue decomposition: dynamics and effect on some soil properties. Cienc. suelo [online]. 2018, vol.36, n.2, pp.129-141. ISSN 1850-2067.

Green bridge crops (CPV) effect on soil and succeeding cash crops depends on the type of CPV and on how their residues decompose. We hypothesized that 1) decomposition rate of grass CPV is lower than that of legume CPV; 2) decomposition dynamics of CPV legume will lead to a higher and faster availability of nitrogen (N); and 3) residue decomposition will lead to a higher but delayed increase of labile soil organic matter fractions with grass CPV and when located on soil surface. We carried out an experiment on a Typic Argiudoll with CPV with oats (Avena sativa L.), vetch (Vicia villosa Roth.) and a control without CPV (TE). Equal amounts of chopped residues of both CPV were placed on surface and mixed with soil (buried). We took soil samples at 0-20 cm in 7 moments along 133 days to determine remnant residue (CR), carbon (C), total (COT), and particulate organic C (COP), ammonium N freed in anaerobiosis (NAN), and nitrate N (N-NO₃ -). Remnant C of both CPV decreased over time, but at a higher rate when buried with differences between vetch and oats. On surface, vetch residues decomposed faster than oats residues, at the end of the experiment, 60 and 79% of the residues, respectively, had decomposed. Neither COT, COP, nor NAN changed along the experiment. After oats, COT and COP (75.1 y 18.6 Mg ha^-1, respectively) were higher than after vetch and TE (70.4 y 16.8 Mg ha^-1, respectively). Besides, these were lower when residues were buried (69.7 y 15.,9 Mg ha^-1, respectively) than when residues were left on surface (73.3 y 18.9 Mg ha^-1, respectively). The position of residues did not affect NAN, but it was higher after oats and vetch (63.1 mg kg^-1) than after TE (50.2 mg kg^-1). Up to 49 days from the start of the experiment there was an increase of N-NO₃ - (45 up to 108 kg ha^-1). N-NO₃ - was higher when CPV was vetch and there was no difference between oats and TE. We did no collect enough evidence to reject the first and the second hypothesis, but evidences were enough to reject the third one.

Keywords : cover crops; green manure; particulate organic matter; anaerobic nitrogen.

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