Resumo

FERNANDEZ, Romina et al. Water, nitrogen and sulphur availability in fallows with and without weed control and different residue levels. Cienc. suelo [online]. 2009, vol.27, n.1, pp.57-66. ISSN 1850-2067.

In order to study the effect of crop residues on the efficiency of water storage, available nitrogen and sulphate dynamics during fallow with and without weed presence, ten experiments with different levels of residue (A: 10,000 kg MS ha^-1, M: 5,000 kg MS ha^-1, B: less than 2,000 kg MS ha^-1) were set up in Haplustolls of the tosca and dune plains in La Pampa and south of Córdoba. Each residue treatment was divided into sub-plots with different weed management: without weed control (malezas) and with control (barbecho). Soil texture, bulk density, permanent wilting pint, and organic matter were determined in each site. At the beginning and end of fallow soil water contents, nitrate (N) and soluble and adsorbed sulphates (S) were measured in samples from 0 -0.2m depth. At all sites the water content at the beginning of fallow was high (between 51 and 100% available water). Despite this, our results showed a positive effect of residue level on water contents at the end of fallow, with a mean difference between A and B of 33%. In weed treatments no effect of residue was observed, and the difference between A and B was 10%. Water contents were more strongly affected by the presence of weeds than by residue level. Available N and S contents showed no effect of residue level, but were strongly affected by weed presence. In weed treatments sunflower seeding would be severely limited by lower available water contents, and the expectable yields would be diminished by 200 kg ha^-1 or 600 kg ha^-1 due to the lower availability of N and S respectively.

Palavras-chave : Sunflower; Semiarid region; Haplustolls; Tosca plains; Dune plains.

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