New agricultural practices and land-use intensification in the Cerrado biome have affected the soil carbon stocks. A major part of the native vegetation of the Brazilian Cerrado, a tropical savanna-like ecoregion, has been replaced by crops, which has caused changes in the soil carbon (C) stocks. To ensure the sustainability of this intensified agricultural production, actions have been taken to increase soil C stocks and mitigate greenhouse gas emissions. In the last two decades, new agricultural practices have been adopted in the Cerrado region, and their impact on C stocks needs to be better understood. This subject has been addressed in a systematic review of the existing data in the literature, consisting of 63 articles from the Scopus database. Our review showed that the replacement of Cerrado vegetation by crop species decreased the original soil C stocks (depth 0–30 cm) by 73%, with a peak loss of 61.14 Mg ha−1. However, when analyzing the 0–100 cm layer, 52.4% of the C stock data were higher under cultivated areas than in native Cerrado soils, with a peak gain of 93.6 Mg ha−1. The agricultural practices implemented in the Brazilian Cerrado make low-carbon agriculture in this biome possible.
The objective of this work was to evaluate soil carbon fractions under cover crops cultivated after corn (Zea mays), with or without nitrogen topdressing fertilization, in a long-term experiment in the Brazilian Cerrado. The experiment was carried out in a randomized complete block design, in split-plots with three replicates. The plots were represented by the cover crops, and the subplots, by the presence or absence of N topdressing for corn. The following cover crop species were planted after the harvest of the 30F53VYHR corn hybrid: 'BRS Mandarin' pigeonpea (Cajanus cajan), sunn hemp (Crotalaria juncea), oilseed radish (Raphanus sativus), and black mucuna (Mucuna aterrima). After the cutting of the cover crops, soil samples were collected at 0.0‒0.10 and 0.10‒0.20 m soil depths. After corn harvest, samples of its residues were taken. The cover crops alter the soil chemical and physical fractions, especially fulvic acid and soil particulate organic carbon. Nitrogen topdressing for corn decreases fulvic acid, but increases the humic acid/fulvic acid ratio and particulate organic carbon in the deeper soil layer.
Nitrous oxide (N2O) emissions resulting from nitrogen (N) fertilization have been documented. However, no data on the effects of other nutrients, such as phosphate (P) and potassium (K), on N2O emissions in integrated crop–livestock systems are available so far. In the 2015/2016 and 2016/2017 growing seasons, we measured N2O emissions from a long-term system, established in 1991 in the Cerrado biome (a tropical savanna ecoregion in Brazil), fertilized with two P and K levels. The studied no-tillage farming systems consisted of continuous crops fertilized with half of the recommended P and K rates (CC-F1), continuous crops at the recommended P and K rates (CC-F2), an integrated crop–livestock system with half of the recommended P and K rates (ICL-F1), and an integrated crop–livestock at the recommended P and K rates (ICL-F2). The cumulative N2O emissions (603 days) and soil chemical properties were analyzed as a 2 × 2 factorial design (long-term agricultural systems x fertilization). The cumulative N2O emissions from CC-F2 and ICL-F1 were 2.74 and 1.12 kg N ha−1, respectively. The yield-scaled N2O emissions from soybean were 55.5% lower from ICL-F1 than from CC-F2 in the 2015/2016 growing season. For off-season sorghum, the mean yield-scaled N2O emissions were 216 mg N2O m−2 kg−1 (in a range from 79.83 to 363.52 mg N2O m−2 kg−1, for ICL-F2 and CC-F1, respectively). The absence of pasture and the presence of soybean and sorghum promoted the highest cumulative N2O emissions, favored by the recommended rate in relation to half of the P and K. In the total evaluation period (603 days), the presence of grazed land in the years prior to this study and land fertilized with half the recommended P and K rates in an integrated crop–livestock system reduced the resulting cumulative N2O emissions by 59%. Thus, we conclude that crop–livestock systems can be beneficial in reducing P and K applications and also in mitigating N2O emissions in comparison with continuous cropping systems fertilized with the full recommended P and K rates. In view of the global fertilizer crisis, this aspect is extremely relevant for agriculture in Brazil and around the world.
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