Abstract
Soil aggregation and the distribution of total organic carbon (TOC) may be affected by soil tillage and cover crops. The objective of this study was to determine the effects of crop rotation with cover crops on soil aggregation, TOC concentration in the soil aggregate fractions, and soil bulk density under a no-tillage system (NTS) and conventional tillage system (CTS, one plowing and two disking). This was a three-year study with cover crop/rice/cover crop/rice rotations in the Brazilian Cerrado. A randomized block experimental design with six treatments and three replications was used. The cover crops (treatments) were: fallow, Panicum maximum, Brachiaria ruziziensis, Brachiaria brizantha, and millet (Pennisetum glaucum). An additional treatment, fallow plus CTS, was included as a control. Soil samples were collected at the depths of 0.00-0.05 m, 0.05-0.10 m, and 0.10-0.20 m after the second rice harvest. The treatments under the NTS led to greater stability in the soil aggregates (ranging from 86.33 to 95.37 %) than fallow plus CTS (ranging from 74.62 to 85.94 %). Fallow plus CTS showed the highest number of aggregates smaller than 2 mm. The cover crops affected soil bulk density differently, and the millet treatment in the NTS had the lowest values. The cover crops without incorporation provided the greatest accumulation of TOC in the soil surface layers. The TOC concentration was positively correlated with the aggregate stability index in all layers and negatively correlated with bulk density in the 0.00-0.10 m layer.
Highlights
IntroductionSoil aggregation is an important factor for plant growth and directly affects water infiltration, the structure of the microbial community, soil biodiversity, soil biomass dynamics, nutrient adsorption and desorption, oxygen availability to the roots, and soil erosion (Denef et al, 2001; Franzluebbers, 2002; Six et al, 2004; Madari et al, 2005; Souza et al, 2009; An et al, 2010). Six et al (2004) added that all of these processes greatly affect soil organic matter (SOM) dynamics and nutrient cycling
Aggregates bigger than 8 mm had the lowest values under the fallow plus CTS treatment (8.90 dag kg-1), which differed from all other treatments under the no-tillage system (NTS)
It was found that mean weight diameter (MWD) values under fallow (7.591 mm), B. brizantha (8.619 mm), B. ruziziensis (7.372 mm), and P. maximum (7.617 mm) were higher than under the fallow plus CTS treatment (3.371 mm)
Summary
Soil aggregation is an important factor for plant growth and directly affects water infiltration, the structure of the microbial community, soil biodiversity, soil biomass dynamics, nutrient adsorption and desorption, oxygen availability to the roots, and soil erosion (Denef et al, 2001; Franzluebbers, 2002; Six et al, 2004; Madari et al, 2005; Souza et al, 2009; An et al, 2010). Six et al (2004) added that all of these processes greatly affect soil organic matter (SOM) dynamics and nutrient cycling. Soil aggregation is an important factor for plant growth and directly affects water infiltration, the structure of the microbial community, soil biodiversity, soil biomass dynamics, nutrient adsorption and desorption, oxygen availability to the roots, and soil erosion (Denef et al, 2001; Franzluebbers, 2002; Six et al, 2004; Madari et al, 2005; Souza et al, 2009; An et al, 2010). Calonego and Rosolem (2008) reported that cover crops increased soil aggregates because of exudates from plant roots. Cover crops and their residues protect soil aggregates against the impact of rainfall and variations in soil moisture and temperature (Bronick and Lal, 2005)
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