Carbon and nitrogen stocks in a Rhodic Nitisol under different tillage methods and mineral and organic fertilizers

Abstract

ABSTRACT Changes in soil management, for example by more vigorous crops, adoption of conservation tillage and optimization of fertilization, can increase soil organic carbon (SOC) and total nitrogen (TN) stocks. We hypothesized that corn - black oat rotation under no-tillage (NT) and adequate soil fertilization can increase these stocks, compared to conventional tillage (CT). This study compared these two tillage methods and organic with mineral fertilizers, regarding their effects on C and N cycling and SOC and TN stocks in a Rhodic Nitisol in southern Brazil. The study started in 2012, in a pasture area, which was converted into corn (Zea mays L.) - black oat (Avena strigosa Scherb.) rotation. The treatments were applied in a 2 × 5 factorial arrangement, consisting of two soil tillage methods (NT and CT) and five fertilizers (pig slurry (PS); biodigested PS (PS-B); composted PS (PS-C); mineral fertilizer; and a control). From 2019 onwards, treatment PS-B was replaced by injected PS (PS-I) and PS-C by poultry litter (PL). A randomized block design was used in a split-plot arrangement, where the plots corresponded to soil tillage and subplots to fertilization. In every year of the study, corn was fertilized with 140 kg N ha -1 and at least 115 kg P 2 O 5 ha -1 and 77 kg K 2 O ha -1 . Total SOC and TN stocks were determined in six soil layers (0.00-0.05, 0.05-0.10, 0.10-0.20, 0.20-0.30, 0.30-0.40 and 0.40-0.60 m) whereas the soil particulate (POC and PN) and mineral-associated (MAOC and MAN) fractions were evaluated in the four upper layers (0.00-0.05, 0.05-0.10, 0.10-0.20, 0.20-0.30m) at the beginning of the study (2012) and after nine years (2021). The cumulative values under NT showed that SOC stocks nearly doubled, compared to those under CT. These increases occurred in the most labile POC and PN fractions. However, no difference in response to the different fertilizers was observed in these stocks. The studied factors indicated a marked effect of soil tillage on alterations in C and N stocks. No-tillage increases SOC and TN stocks, mainly in the most labile fractions (POC and PN) of Rhodic Nitisols in southern Brazil, under corn - black oat rotation.