ABSTRACT Afforestation of sites disturbed after bauxite mining is the favorite technique to restore all ecosystem functions. The nature of the tree species used for revegetation of post-mining land can accelerate the recovery of soil organic matter and nutrient cycles. This study aimed to determine the litterfall production, decomposition rate and nutrient content from three types of forest cover ( Eucalyptus , Anadenanthera peregrina , mixed plantation of 16 native species) planted in a bauxite mining area in recovery. Litterfall production was evaluated monthly over 30 months, and the litter mass was assessed twice a year (dry and rainy periods). Total nutrient content was determined from samples grouped by period (dry and rainy). The annual average values for litterfall dry mass and litter mass were higher in Eucalyptus and mixed native. The period (dry or rainy) did not influence litterfall rates in A. peregrina , but Eucalyptus and mixed native presented higher amounts for litterfall during the rainy and dry periods, respectively. Litter accumulation in Eucalyptus was not affected by the season of the year, but mixed native and A. peregrina presented higher litter accumulation in the dry season. Apparent decomposition rates of A. peregrina and mixed native were higher in the rainy season, highlighting the A. peregrina with the highest values compared with the other forest covers. The mixed native presented the highest leaf content of P, K, Ca and Mg in both the litterfall and litter mass, while Eucalyptus had the lowest P, K, Ca, S and N content and the highest C content in the litterfall. Litterfall production is important in degraded areas to ensure the nutrient return to the soil. The data obtained suggest that the cultivation of a mixed of 16 native trees contribute for produce the higher annual litterfall yields, besides produces leaf litterfall of better nutritional quality in relation to P, K, Ca, Mg and S. Therefore, mixed of native trees can be a promising option for reactivation of nutrient cycling and organic matter formation in mined area of bauxite in the Brazilian Atlantic Forest.

ABSTRACT Understanding soil organic matter (SOM) dynamics in production systems on tropical soils is necessary to guide strategies to increase SOM formation. This study aimed to evaluate soil carbon (C) dynamics by combining applications of different plant residues used on tropical soils. An incubation study was carried out with and without adding millet (Pennisetum americanum) residues combined with six crop residues (legumes and non-legumes); and one additional treatment with only millet residue. Higher C-CO2 fluxes recorded in jack bean, sunflower and velvet bean residues were correlated with high soluble compound contents (49.5, 49.6 and 32.1 %, respectively). Adding millet residues resulted in positive PE for all residue combinations. Soils without millet, except jack bean, had a negative PE. Residues application promoted four times increase in C-POM content (from 1.04 to 4.2 g kg-1 soil). The C-MAOM content had 2.4 times increase, being more expressive due to its high initial content (from 15.3 to 37.3 g kg-1 soil). The comparison between the final C contents in the SOM fractions showed a significant increase of 8.8 times for MAOM in relation to POM, demonstrating the larger dimension of this C reservoir in the soil. Both combinations of legumes + non-legumes and non-legume + non-legume contributed significantly to the conversion of C to MAOM. The results give insight into possible management strategies for significant C increments in the more stable SOM fractions, depending on the residue type (quality) and residue combination.

ABSTRACT Rational management of spontaneous plants is an alternative for increasing productivity in tree crops. This study aimed to evaluate the impact of management systems between rows and under the canopy of early dwarf cashew trees on the soil chemical properties and light-fraction organic matter and cashew root systems; we also evaluated the nutrient inputs from the spontaneous plants phytomass and cashew leaves deposited on an Arenic Kandiustults. The management systems under study were disc harrowing (DH) and mechanical mowing (MM) between rows, both with clearing under the cashew canopy (crowning), and herbicide (HERB) between the rows and under the canopy (without crowning). Soil and plant samples (leaves, stems, and roots) were collected at three points: under the canopy, at the canopy projected limit, and between the rows of cashew plants, all after seven years of conducting the experiment. Soil samples collected at the layers of 0.00-0.05, 0.05-0.10, 0.10-0.20, and 0.20-0.30 m were evaluated for total organic carbon, light-fraction organic matter, and chemical attributes. Dry matter, Na, Ca, Mg, N, P, and K were determined in the spontaneous-plant phytomass from under the canopy, at the canopy projected limit, and between the rows. Results showed that between rows of cashew trees there are higher phytomass input and increases in the light fraction of organic matter, pH and Mg2+ in the soil in the treatment MM. Not removing crop residues or spontaneous plants by crowning promoted accumulation of organic material and higher contents of nutrients under the canopy. The management of spontaneous plants and also soil surface under the canopy of the cashew plants had a great influence on productivity. The crowning, used in MM and DH, led to lower productivity, 1,171.87 and 594.97 kg ha-1, respectively, when compared with the absence of crowning (HERB), which resulted in productivity of 1,363.80 kg ha-1. The practice of crowning is not recommended for soil management systems in dwarf cashew crops.

RESUMO O uso de fertilizantes com alguma proteção aos íons fosfato pode diminuir sua adsorção pelo solo e aumentar a absorção pela cultura, o que aumenta a eficiência da adubação. O objetivo deste trabalho foi avaliar o desempenho de um fertilizante fosfatado associado a biocarvão em um solo com alta capacidade de fixação de P. Os biocarvões foram produzidos a partir de duas fontes de biomassa: bagaço de cana-de-açúcar (BC) e serragem de madeira (SM), as quais foram pirolisadas em duas temperaturas (350 °C e 700 °C). Após a caracterização química e física, os biocarvões foram granulados com superfosfato triplo (TSP) em uma proporção 3:1 (TSP: biocarvão). A avaliação agronômica dos fertilizantes foi realizada por dois cultivos sucessivos de milho (Zea mays L.) em casa de vegetação em Latossolo argiloso em esquema fatorial (5x3) em delineamento de blocos inteiramente casualizados com 4 repetições. Os tratamentos consistiram de cinco fertilizantes (TSP-SM350, TSP-SM700, TSP-BC350, TSP-BC700 and TSP) e três doses de P (100, 200 e 400 mg dm-³ de P). Foram avaliados a produção de massa de matéria seca, acúmulo de P no milho, além do P disponível no solo após os cultivos. A produção de matéria seca, conteúdo de P na planta e P disponível no solo apresentou resultados superiores em ambos os cultivos na dose de 400 mg dm-3, já a taxa de recuperação aumentou de forma inversa em relação as doses. A simples associação de biocarvão com fertilizante fosfatado solúvel não aumentou a eficiência de uso de P pelo milho, mas aumentou o P disponível no solo após dois cultivos sucessivos.

ABSTRACT The use of fertilizers with some degree of protection of the phosphate ions can reduce soil adsorption and increase the absorption by plants, increasing the efficiency of phosphorus (P) fertilization. This study aimed to evaluate the performance of a phosphate fertilizer associated with biochar in granules in a P-fixing soil in a greenhouse experiment. Biochars were produced from two sources of biomass: sugarcane bagasse (SB) and wood sawdust (WS), which were pyrolysed at two temperatures (350 °C and 700 °C). After chemical and physical characterization, the biochar samples were granulated with triple superphosphate (TSP) in a 3:1 ratio (TSP: biochar). The agronomic evaluation of the fertilizers was carried out by two successive maize crops (Zea mays L.) in the greenhouse, using a factorial scheme of (5x3) in randomized block design with four replicates. The treatments consisted of five fertilizers (TSP-WS350, TSP-WS700, TSP-SB350, TSP-SB700, and TSP) and three P doses (100, 200, and 400 mg dm-3). It was evaluated the dry matter production, P uptake in maize and P available in the soil after cultivation. The results indicate that dry matter production, considering the P uptake by the plant and the P available in the soil when using a dose of 400 mg dm-3, presented higher results in both crop cycles and the recovery rate in both cultivations occurred inversely to the P doses. The simple association of biochar with soluble phosphate fertilizer did not increase the efficiency of P use by maize, but it increased available P in soil.

RESUMO O uso de estimulantes para o estabelecimento de fungos micorrízicos arbusculares tem grande potencial em contribuir para a absorção de P pelas plantas. Objetivou-se avaliar a eficácia do isoflavonóide formononetina como estimulante da micorrização na cultura da soja, associada a adubação fosfatada, em dois Latossolos com teores de fósforo disponível médio (LPm) e baixo (LPb) no Cerrado piauiense. O delineamento experimental em cada solo foi em blocos casualizados no esquema fatorial 4×4, com quatro repetições. Os tratamentos foram constituídos por quatro doses de fósforo (0; 26,66; 40 e 80 kg ha-1 de P2O5) e quatro doses do isoflavonóide formononetina (0; 0,5; 0,9 e 1,8 g kg-1 de semente de soja). As variáveis avaliadas foram, o crescimento, a produção, a nodulação e taxa de colonização micorrízica da soja. Com exceção da taxa de colonização micorrízica no LPm, altura e número de vagens por planta de soja no LPb, as demais variáveis, não foram influenciados pela aplicação do isoflavonóide formononetina, em ambos os solos. A produtividade cresceu linearmente ao incremento das doses de fósforo no LPb, apresentando uma eficiência agronômica de ~15 kg ha-1 de grãos para cada kg ha-1 de P2O5 aplicado no solo.

ABSTRACT The use of stimulants in the establishment of arbuscular mycorrhizal fungi has great potential in contributing to P uptake by plants. This study aimed to evaluate the effect of isoflavonoid formononetin as mycorrhization stimulant on soybean associated with phosphate fertilizer in Oxisols with intermediate (OPi) and low (OPl) phosphorus availability, in the Cerrado region of Piauí. The experiment in each soil consisted of randomized blocks design in a 4×4 factorial scheme, with four replications. The treatments comprised of four phosphorus doses (0, 26.66, 40 and 80 kg ha-1 P2O5), and four isoflavonoid formononetin doses (0, 0.5, 0.9 and 1.8 g kg-1 soybean seeds). The variables evaluated were soybean growth, yield, nodulation and mycorrhizal colonization rate. With the exception of mycorrhizal colonization rate in OPi, plant height and number of pods per plant in OPl, the other variables were not affected by the application of isoflavonoid formononetin, in both soils. Yield linearly increased with increase in the phosphorus doses in OPl, and presented agronomic efficiency of ~15 kg ha-1 grain for each kg ha-1 P2O5 applied to the soil.

A utilização do solo sob Cerrado tem acarretado modificações nas suas propriedades, bem como no comportamento e qualidade da sua matéria orgânica. O Cerrado piauiense vem sendo alvo de exploração sem a devida preocupação com a manutenção dos recursos naturais, onde os sistemas de produção têm se caracterizado pelo uso intensivo do solo. O objetivo desta pesquisa foi avaliar o efeito da utilização agrícola na alteração dos atributos biológicos e na dinâmica da matéria orgânica em Latossolos Amarelos distróficos típicos, cultivados com soja. O trabalho foi realizado na Serra do Quilombo, localizada no Cerrado piauiense. Foram verificadas as alterações nos atributos do solo em decorrência da utilização agrícola, que foi iniciada com plantio convencional, posteriormente substituído pelo sistema plantio direto. Foram amostrados solos com diferentes históricos de uso: PC7/PD8 - sete anos de plantio convencional e oito de plantio direto; PC5/PD4 - cinco anos de plantio convencional e quatro de plantio direto; PC3/PD3 - três anos de plantio convencional e três de plantio direto; e CN - solo com Cerrado nativo. Os atributos avaliados foram: respiração basal do solo, carbono da biomassa microbiana, quociente metabólico, quociente microbiano, carbono orgânico total e nitrogênio total. Para avaliar a dinâmica da matéria orgânica, foi feito o fracionamento físico. Os dados foram submetidos à análise de variância. Os resultados indicaram que o manejo imposto ao solo com cultivo convencional e posterior implantação do sistema plantio direto contribuiu para alterar as propriedades biológicas do solo, em comparação com o Cerrado nativo. A substituição do Cerrado nativo por culturas anuais sob o sistema plantio direto reduz os teores de carbono da biomassa microbiana e de nitrogênio total e eleva a respiração basal nos tratamentos com três e quatro anos de implantação do plantio direto, indicando que esse tempo é insuficiente para melhoria desses atributos. O aumento do tempo de uso do solo com plantio direto diminui o teor de C particulado e mantém o de C associado aos minerais, em comparação ao solo do Cerrado nativo.

The intensive use of soils in the Cerrado biome has caused modifications in soil properties, as well as in the performance and quality of organic matter. The Cerrado of Piauí has been exploited without due concern for the preservation of natural resources, where production systems are characterized by intensive land use. The objective of this research was to evaluate the effect of the agricultural use in altering the biological properties and dynamics of organic matter of Yellow Oxisols cultivated with soybean. This research was carried out in the "Serra do Quilombo", located in the Cerrado region of Piauí state. To assess changes in soil properties, induced by agricultural use, soil samples were collected from sites with different use history involving conventional and no tillage systems; PC7/PD8 - seven years of conventional agriculture followed by eight years of no-tillage; PC5/PD4 - five years of conventional system followed by four years of no-tillage; PC3/PD3 - three years of conventional system and three years of no-tillage and CN - native cerrado vegetation. The evaluated soil properties were basal respiration, microbial biomass C, metabolic quotient, microbial quotient, total organic C and total N. Physical fractionation was used to evaluate organic matter dynamics. The results were subjected to variance analysis and showed that the soil management under conventional cultivation and subsequent implantation of no-tillage system affected soil biological properties in relation to the soil under native cerrado vegetation. The replacement of native cerrado by annual no-tillage crops reduces the levels of microbial biomass C and total N and elevates the basal respiration in treatments after three and four years of no tillage, indicating that these periods are insufficient to improve the above properties. The increase in the time of land use with no tillage decreases the level of particulate organic C and maintains the C-associated minerals in relation to the soil under native cerrado vegetation.