Cover crop rotations in no-till system: short-term CO2 emissions and soybean yield

Abstract

In addition to improving sustainability in cropping systems, the use of a spring and winter crop rotation system may be a viable option for mitigating soil CO 2 emissions (ECO 2 ). This study aimed to determine short-term ECO 2 as affected by crop rotations and soil management over one soybean cycle in two no-till experiments, and to assess the soybean yields with the lowest ECO 2 . Two experiments were carried out in fall-winter as follows: i) triticale and sunflower were grown in Typic Rhodudalf (TR), and ii) ruzigrass, grain sorghum, and ruzigrass + grain sorghum were grown in Rhodic Hapludox (RH). In the spring, pearl millet, sunn hemp, and forage sorghum were grown in both experiments. In addition, in TR a fallow treatment was also applied in the spring. Soybean was grown every year in the summer, and ECO 2 were recorded during the growing period. The average ECO 2 was 0.58 and 0.84 g m 2 h −1 with accumulated ECO 2 of 5,268and 7,813 kg ha -1 C-CO 2 in TR and RH, respectively. Sunn hemp, when compared to pearl millet, resulted in lower ECO 2 by up to 12 % and an increase in soybean yield of 9% in TR. In RH, under the winter crop Ruzigrazz+Sorghum, ECO 2 were lower by 17%, although with the same soybean yield. Soil moisture and N content of crop residues are the main drivers of ECO 2 and soil clay content seems to play an important role in ECO 2 that is worthy of further studies. In conclusion, sunn hemp in crop rotation may be utilized to mitigate ECO 2 and improve soybean yield.

Soil carbon fluxes and balances of crop rotations under long-term no-till

“…Higher CO 2 flux was expected at the beginning of soybean seasons, as it coincides with the high residue mineralization rates [14,46,47]. However, the lower rainfall events associated with high Tsoil, mainly in 2013 [(between December 2013 to January 2014), Fig.…”

“…3), allowed the soil cover, in addition to the grain yield, of around of 1.4 Mg ha −1 (data not shown). In contrast, cropping sunflower has been inefficient for grain yield production, as observed in previous years [14,30], even though sunflowers are considered drought tolerant [31]. Typically, grass species have greater potential to produce biomass mainly under water deficit conditions and the residue composition with esterified acetylated lignin complexes [32], which implies slower decomposition.…”

“…Typically, grass species have greater potential to produce biomass mainly under water deficit conditions and the residue composition with esterified acetylated lignin complexes [32], which implies slower decomposition. Besides the amount of crop residue on soil surface, it is important to highlight the quality of crop residues, characterized by biochemical composition and C/N ratios, which stimulates the mineralization or persistence on soil surface [7,14,30]. Therefore, C losses must be offset compensated by an increase in the amount of crop residues on the soil surface, either by cover crops as well as by cash crops.…”

“…Cropping systems increase the microbial community dynamics compared to bare fallow soil [52]. The contribution of labile C from cover crop residue and their quality are the main factors influencing the microbial biomass and community structure [53,54], and according to the mineralization rate may stimulate the CO 2 flux [14].…”

“…Quality parameters of crop residues such as nitrogen (N) content, lignin and polyphenols could alter the dynamics of soil C and N, and microbial activity [17,18], and the rate of mineralization and consequently CO 2 emitted to the atmosphere [14].…”