26-06-2012, 02:07 PM
Soil microbial biomass and organic matter fractions during transition from conventional to organic farming systems
Soil microbial biomass and organic matter fractions.pdf (Size: 163.22 KB / Downloads: 72)
Introduction
Conventional farming has played an important role in the improvement
of food and fiber productivity to support human demands
but it has been largely dependent of synthetic fertilizers, pesticides
and herbicides (Tu et al., 2006). On the other hand, organic farming
avoids the use of synthetic fertilizers and pesticides and emphasizes
organic inputs for nutrient supply and biological processes for pest
management (Araújo et al., 2008). This system increases at an annual
rate of 20% accounting approximately 24 million hectares in the entire
world (Willer and Yussefi, 2004). Brazil has approximately 850
thousand hectares occupied by organic farming (Willer and Yussefi,
2007) and, specifically, the northeast region produces organic fruits
to support international market demands over recent years (Leite et
al., 2010).
Materials and methods
Study area
The field study was carried out at Parnaíba (03° 05′ S; 41° 47′ W;
46 m), Piauí state, Northeast Brazil. The climate is rather dry with a
mean precipitation of 1000 mm year−1 and an annual mean temperature
of 30 °C. The soil type is a Typic Quartzipsamment in the US soil
taxonomy. Soil samples were obtained in March 2010 from the following
plots: “acerola” orchard (Malpighia glaba) under 10 years of
conventional farming (CON); “acerola” orchard (Malpighia glaba)
under 2 years of transitional period from conventional to organic
farming (TRA); “acerola” orchard (Malpighia glaba) under 5 years
of organic farming (ORG); native vegetation (NV). The size of each
experimental plot is 1000 m2.
Results
Soil organic carbon and humic substances
SOC contents were higher in the ORG at 0–5 cm and 5–10 cm
depths. However, at 10–20 and 20–40 cm depths no differences
were observed. ORG also showed higher TN contents in the all evaluated
depths (Table 3). TRA and NV showed similar values for SOC and
TN in all depths, except for SOC at 5–10 cm depth. Higher differences
were observed between ORG and CON, i.e.74% (0–5 cm) and 69%
(5–10 cm) for SOC and 66% (0–5 cm), 63% (5–10 cm), 51% (10–20 cm)
and 67% (20–40 cm) for TN contents. In addition, SOC contents were
26% and 42% higher in ORG than NV (reference) at 0–5 cm and
5–10 cm, respectively.