ABSTRACT Management of Quilombola systems are primitive agricultural systems based on the ancestral knowledge of Afro-Brazilian enslaved people. Here, the aim was to understand the impact of these primitive farming methods on the distribution of available nitrogen (N) forms in the soil profile of two Brazilian Cerrado phytophysiognomies. The soil was sampled in Cerradão (high Cerrado) and Cerrado Stricto sensu (low Cerrado) at six soil depths (0-10, 10-20, 20-30, 30-40, 40-50, and 50-60 cm). The following management systems were considered: pasture (PP1 and PP2), maize cultivation (M1 and M2), citrus-cassava intercropping (T1), and citrus monoculture (T2). In addition, the soil was sampled in the native area of Cerradão (NC1) and Cerrado Stricto sensu (NC2). Three N forms were determined: i) available nitrogen (Av-N), ii) ammonium (NH4+-N) and iii) nitrate (NO3–-N) contents. The Av-N content decreased with increasing soil depth only in NC1 and NC2. The NO3–-N content was similar at all soil depths for maize and pasture, while the content decreased at soil depth for NC1, NC2, and T1. NH4+-N was similar in M2 and PP2, but it increased in T2, ranging from 6.17 mg kg–1 to 17.54 mg kg–1. Overall, the dynamics of available N forms varied according to the Cerrado phytophysiognomy and the management systems and NO3–-N was the most constant N form in the soil profile. Therefore, although the management of Quilombola systems is less intensive, they negatively affect the dynamics and N availability, mainly where management is less conservative, that is, in maize and citrus monocultures.

Resumo: O objetivo deste trabalho foi avaliar as frações de carbono no solo, sob plantas de cobertura cultivadas em sucessão ao milho (Zea mays), com ou sem adubação nitrogenada em cobertura, em um experimento de longa duração no Cerrado brasileiro. O experimento foi conduzido em delineamento de blocos ao acaso, em parcelas subdivididas, com três repetições. As parcelas consistiram das plantas de cobertura, e as subparcelas, da presença ou da ausência de adubação nitrogenada em cobertura para o milho. As seguintes plantas de cobertura foram plantadas, após a colheita do milho híbrido 30F53VYHR: guandu 'BRS Mandarim' (Cajanus cajan), crotalária (Crotalaria juncea), nabo-forrageiro (Raphanus sativus) e mucuna-preta (Mucuna aterrima). Após o corte das plantas de cobertura, amostras de solo foram coletadas às profundidades de 0,0‒0,10 e 0,10‒0,20 m. Após a colheita do milho, seus resíduos culturais foram coletados. As plantas de cobertura alteram as frações químicas e físicas do solo, principalmente o ácido fúlvico e o carbono orgânico particulado. A fertilização de N em cobertura no milho diminui o ácido fúlvico, mas aumenta a razão ácido húmico/ácido fúlvico e o carbono orgânico particulado na camada mais profunda do solo.

Abstract: 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.

ABSTRACT: Soil management systems exert different effects on soil attributes, especially on the organic matter content, and, consequently, the soil aggregation. The aim of this study was to evaluate the impact of different land uses practiced by quilombola family farmers on water stable aggregates, glomalin and organic carbon in soil aggregates. Soil samples were collected at depths of 0-10 and 10-20 cm from areas cultivated under the following management systems: 1) conventional corn plantation (MA), 2) cultivation of citrus trees intercropped with annual crops (AC) (a conservationist approach), 3) pasture of Brachiaria (Urochloa spp.) (PA), and, as reference, an area of the Cerrado (CR) free of any anthropogenic interference. The studied areas were evaluated in a completely randomized design, with five replications, in a subplot scheme. The plots were the management systems and the subplots the depths. Soil macro-aggregates were predominant at both depths and the aggregate stability indices were higher than 90 % for all management systems. Total organic carbon in the two aggregate classes (micro and macro-aggregates) correlated with the MWD (mean weight-diameter), but not with the easily extractable glomalin (EEG) related soil protein. Soil micro and macro-aggregates, EEG and MWD discriminated management systems and are important soil quality indicators. The carbon content in both micro-aggregates (C-MIC) and macro-aggregates (C-MAC) of the intercropped system (AC) was higher than in the CR. The soil attributes that best separated the areas were C-MIC, MWD and EEG in macro-aggregates for the depth of 0-10 cm, and EEG in micro-aggregates, together with MWD and C-MAC for the depth of 10-20 cm.