Effect of 26-years of soil tillage systems and winter cover crops on C and N stocks in a Southern Brazilian Oxisol

Abstract

Soil management and crop rotation are key factors in controlling the accumulation of C and N in the soil profile, but their long-term effect remains poorly understood for deep soil layers, especially in subtropical conditions. Using a long-term experiment (26-years), this study aimed to evaluate the effect of different soil management systems associated with different winter cover crops on C and N accumulation in a very clayey (72 % clay) soil up to 1 m deep. Two tillage systems [conventional tillage (CT) and no-tillage (NT)] were cultivated with eight winter cover crops (black oat, rye, common vetch, hairy vetch, oilseed radish, wheat, blue lupine, and fallow) in a subtropical Oxisol from Southern Brazil. Soil samples were taken in eight soil layers up to 1.00 m soil depth after 26 years of experiment and, also from an adjacent native forest. After forest clearing, the C stock in the 0.00-0.20 m soil layer was reduced by 45 % in only 10 years (from 1976 to 1986) of soil tillage. Twenty-six years after the beginning of the experiment, C and N stock in 0.00-0.20 m soil layer were 13 and 20 % higher in NT compared to CT, with the greatest differences in C and N content observed in the 0.00-0.05 m layer. When associated with winter cover crops, NT accumulated 0.6 and 0.06 Mg ha-1 yr-1 more C and N than CT with winter fallow in the 0.00-0.20 m soil layer. No-tillage and CT recovered 95 and 83 %, respectively, of the C stock found in the 0.00-0.20 m layer from the native forest. However, in the 0.00-1.00 m soil layer, the positive effect of NT on soil C accumulation compared to CT was diluted, and no clear effect of NT was verified. Moreover, no difference in winter cover crops on soil C and N stocks were observed in all soil layers, possibly due to their similar residues input (3.3-4.9 Mg ha-1 yr-1). No-tillage associated with high biomass input through winter cover crops promoted a faster recovery of soil C and N stock than in CT and, therefore, is an efficient tool to improve soil C and N accumulation even in Oxisols with high clay content.

Soil organic matter fractions in an Oxisol under tillage systems and winter cover crops for 26 years in the Brazilian subtropics

“…The effect of NT on C increments occurred mainly in the topsoil layer, and when observing the whole 0-0.20 m soil layer, this effect was weakened and not significant (Fig. 3), which was also checked by Tiecher et al (2020) considering the 0-1.0 m soil layer. Besides that, the effect of NT could be seen in the proportion of POM fractions between the soil layers, in which 56.8% of C of free-POM and 37.7% of occluded-POM was in the superficial layer (Fig.…”

Phosphorus speciation under long‐term crop rotation management in a tropical soil

“…The soil P and soil labile P were significantly ( p < .05) higher under crop rotations compared with native forest (Figure 1a) because of fertilizer application but did not differ among the crop rotation treatments. Continuous straw P inputs over the years in cropped systems can positively impact and improve soil P availability for plants (Calegari et al., 2013; Tiecher et al., 2015), most likely owing to the uptake of P by crop species and recycling back to the soil through crop residues (Soltangheisi et al., 2020). It was expected that long‐term straw returning could enhance soil P content according to the crop rotation species owing to the different potential of cycling P. However, as noted above, no effect of crop rotation on labile P was observed in this study.…”

“…A common strategy for increasing P fertilizer efficiency in cropping systems involves the addition of cover crops in rotation under no‐tillage (NT) management. This approach relies on the different abilities of crop species to acquire less labile soil P (Hallama et al., 2019; Tiecher et al., 2012) and mobilize P (Tang et al., 2021), which impact available soil P (Teles et al., 2017; Tiecher et al., 2015). For example, legumes produce root exudates containing enzymes, organic acids and protons that can mobilize chemically bound forms of P in the soil, while cereals are more efficient in converting acquired P to biomass production (Tang et al., 2021).…”