Use of cover crops in soybean monoculture: effects on water and carbon balance
Cover crops (CC) are a good alternative to improve soil mulch and carbon (C) balance under no tillage with soybean monoculture (Glycine max L. Merr.), predominant in the Pampean Region. This study (2006-2011) evaluated the effect of winter CC –wheat (T), oats (A), vetch (V) and oats+vetch (A+V)- on water consumption, dry matter (MS) production and soil organic carbon contents (COT) using a control (Ct) without CC. Biomass production of the CC was closely related to rainfall recorded between the months of June and October. In general, T and A treatments contributed greater amounts of MS, on average, biomass production was 24 and 91% higher compared to A+V and V. The water cost of including CC was 13-93 mm compared to Ct. At soybean seeding, in general, Ct presented the highest water content. However, this treatment showed a loss of moisture by evaporation without biomass production, which is used by the CC to fix between 18 and 303 kg C ha-1 mm-1 depending on the conditions that year. The use of T, A and A+V increased the COT at a rate of 597 to 98 kg C ha-1yr-1 at 0-25 cm depth, while those without CC and with legumes (V) decreased 824 and 289 kg C ha-1 yr-1, respectively. For conservation or increase of the COT, use of A, A+V and T like CC would be a feasible option given that it exceeds the minimum source C input of 4.5 Mg C ha-1 necessary to maintain the COT south of Santa Fe.
Wheat; oat; vetch; available water; total organic carbon.