Microbial biomass and activity at various soil depths in a Brazilian oxisol after two decades of no-tillage and conventional tillage

• Published in: Soil biology & biochemistry 2010-12, Vol.42 (12), p.2174-2181
• Main Authors: Babujia, L.C., Hungria, M., Franchini, J.C., Brookes, P.C.
• Format: Article
• Language: English
• Subjects: Agronomy. Soil science and plant productions; Biochemistry and biology; Biological and medical sciences; bulk density; carbon; Chemical, physicochemical, biochemical and biological properties; conventional tillage; Cropping systems. Cultivation. Soil tillage; Fundamental and applied biological sciences. Psychology; General agronomy. Plant production; Glycine max; long term effects; long term experiments; Metabolic quotient; microbial activity; Microbial basal respiration; microbial quotient; Microbiology; nitrogen; No-tillage; Organic matter; Oxisols; Physics, chemistry, biochemistry and biology of agricultural and forest soils; Soil carbon; soil density; soil depth; soil fertility; Soil microbial biomass; soil microorganisms; Soil organic matter; soil quality; soil respiration; Soil science; Soil tillage; soybeans; Tillage. Tending. Growth control; Triticum aestivum; winter wheat
• ISSN: 0038-0717; 1879-3428
• DOI: 10.1016/j.soilbio.2010.08.013

The advantages of no-tillage (NT) over conventional tillage (CT) systems in improving soil quality are generally accepted, resulting from benefits in soil physical, chemical and biological properties. However, most evaluations have only considered surface soil layers (maximum 0–30 cm depth), and values have not been corrected to account for changes in soil bulk density. The objective of this study was to estimate a more realistic contribution of the NT to soil fertility, by evaluating C- and N-related soil parameters at the 0–60 cm depth in a 20-year experiment established on an oxisol in southern Brazil, with a soybean (summer)/wheat (winter) crop succession under NT and CT. At full flowering of the soybean crop, soil samples were collected at depths of 0–5, 5–10, 10–20, 20–30, 30–40, 40–50 and 50–60 cm. For the overall 0–60 cm layer, correcting the values for soil bulk density, NT significantly increased the stocks of C (18%) and N (16%) and microbial biomass C (35%) and N (23%) (MB-C and -N) in comparison to CT. Microbial basal respiration and microbial quotient ( qMic) were also significantly increased under NT. When compared with CT, NT resulted in gains of 0.8 Mg C ha −1 yr −1 (67% of which was in the 0–30 cm layer) and 70 kg N ha −1 yr −1 (73% in the 0–30 cm layer). In the 0–5-cm layer, MB-C was 82% higher with NT than with CT; in addition, the 0–30 cm layer accumulated 70% of the MB-C with NT, and 58% with CT. In comparison to CT, the NT system resulted in total inputs of microbial C and N estimated at 38 kg C ha −1 yr −1 and 1.5 kg N ha −1 yr −1, respectively. Apparently, N was the key nutrient limiting C and N stocks, and since adoption of NT resulted in a significant increase of N in soils which were deficient in N, efforts should be focused on increasing N inputs on NT systems.