Winter cover crops in soybean monoculture: Effects on soil organic carbon and its fractions

DUVAL, M; GALANTINI, JA.; CAPURRO, JE; MARTINEZ, JM

SOIL & TILLAGE RESEARCH

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2016 vol. 161 p. 95 - 105

0167-1987

land areas under no tillage (NT), where soybean is the predominant crop. These systems with long periods of fall-winter fallow and poor annual input of carbon (C) into the soil lead to soil degradation, thereby affecting physical and chemical properties. A 6-year cover crop study was carried out on a Typic Argiudoll under NT in the south of Santa Fe, Argentina. Various winter species were used as cover crops: wheat (W), oat (O), vetch (V), an oat + vetch mixture (O + V) and a control (Ct) treatment without a cover crop. We examined the influence of cover crops on the following soil organic C-fractions: coarse particulate organic carbon (POCc), fine particulate organic carbon (POCf) and mineral-associated organic carbon (MOC) from 2008 to 2011. Aboveground carbon input by the cover crops was related to the June to October rainfalls. In general, theWand O treatments supplied a higher amount of C to the soil; these gramineous species produced 22 and 86% more biomass than O + V and V. The water cost of including cover crops ranged from 13 to 93 mm compared with Ct. However, this water-use did not affect soybean yields. On average, gramineous species (pure stand or mixture) supplied more than 3.0 Mg C ha−1 year−1 to the soil, whereas V supplied less than 2.0 Mg C ha−1 year−1. Increase in the mean annual C-input by residues into the soil (cover crop + soybean) explained most SOC variation (R2 = 0.61; p < 0.05). This relationship was more evident with labile soil organic fractions, both for POCc (R2 = 0.91; p < 0.001) and POCc + POCf (R2 = 0.81; p < 0.001). The stratification ratios of SOC (SI, 0?5:10?20 cm) reflected differences among treatments, where >2.0 for W; 1.7 for O, O + V and V, and