Grande parte dos solos amazônicos geralmente são ácidos, com capacidade de troca de cátions e fertilidade baixas, o que os torna limitante para o aumento da produtividade e sustentabilidade dos sistemas agrícolas nesta região. Devido a isso, agricultores familiares estão utilizando áreas de Terra Preta Arqueológica (TPA) para os seus cultivos, pois estas apresentam elevados teores de nutrientes, principalmente fósforo e cálcio (P e Ca). As TPA são decorrentes de atividades humanas pretéritas, portanto, são antigos assentamentos indígenas caracterizados como sítios arqueológicos.  Neste sentido, o objetivo no trabalho foi analisar a disponibilidade de P nos solos de cinco sítios arqueológicos no Município de Oriximiná, Brasil. Foram avaliadas amostras de TPA nas profundidades 0-0,20 e 0,20-0,40 m dos sítios arqueológicos (Maracajá, Faissal, Praia, Juquirizinhos I e II). Os teores de P disponível foram elevados, variando de 4 a 304 mg kg-1. O sítio arqueológico que apresentou o maior teor médio foi o Juquirizinho I, variando de 17 a 202 mg kg-1 de P e o que apresentou menor teor médio foi o Praia, variando de 5 a 20 mg kg-1 de P. Houve grande variação nos teores de P entre os sítios, com destaque para o Juquirizinho I, que apresentou valores entre 17 a 202 mg kg -1. Quatro dos cinco sítios avaliados apresentaram alta disponibilidade de P, mas algumas áreas amostradas apresentaram valores abaixo de 30 mg kg–1, neste sentido não apresentaram horizonte A antrópico. Houve grande variação dos teores de fósforo em profundidade, considerando o mesmo sítio arqueológico.

Cassava is a crop of major socioeconomic importance in Brazil because of its versatility and high yield in nutrient-poor soils. Fertilization can improve soil quality and further increase cassava yield. This study aimed to investigate the effects of different fertilizer sources on soil total organic carbon (TOC) and cassava yield indicators. The experiment was conducted on a family farm in Santarém, Brazil, in a randomized block design, with four treatments and five replications. Treatments were as follows: T1, unfertilized soil (control); T2, NPK fertilizer; T3, poultry manure; and T4, cattle manure. The variables analyzed were soil TOC, shoot fresh weight, plant height, marketable stem diameter, marketable root yield, and yield. Data were subjected to analysis of variance, Tukey’s test (p < 0.05), hierarchical clustering, and principal component analysis. Application of organic fertilizers (T3 and T4) increased soil TOC levels. Chemical fertilizer treatment (T2) resulted in the highest shoot fresh weight, yield, and marketable root yield. Marketable stem diameter was positively influenced by T2 and T4. There were no significant treatment effects on plant height. Hierarchical clustering isolated organic fertilizers (T3 and T4) from other treatments. Principal component analysis revealed two principal components, which together explained 87.77% of the total variance. Organic fertilizer application provided the highest TOC accumulation during the experimental period, whereas NPK fertilization was the most effective in increasing cassava yield in the first year of cultivation

Changes in soil attributes caused by the conversion of native forest for agricultural use in the Amazon region is an area of research because of current uncertainties regarding land use and occupation processes. These uncertainties are significant for tropical soils. Understanding changes in soil attributes is vital for developing strategies to mitigate greenhouse gas emissions in the Amazon region. The objective of this study was to investigate the impact of land use on soil attribute variability occurring in distinctly Amazonian environments. This study was conducted using five meshes in Southern Amazonas: Forest 1, cassava, sugarcane, Forest 2, and Archeological Dark Earth (ADE). Descriptive statistical, geostatistical, and multivariate analyses were performed on data obtained from local measurements of CO2 emissions and data obtained from physical and chemical analysis of soil layers up to a depth of 20 cm. Most physical, chemical, and biological attributes of the soil were related to land use classifications. The similarity between cultivated and forested areas yielded no evidence of land degradation resulting from land use. Increasing certain physical attributes total porosity (PT), soil moisture (SM), and Macroporosity (Macro) yielded a greater increase in the CO2 efflux for ADE and Amazon forest environments than for cultivated regions.

Nutrient management becomes essential in soils with low natural fertility, so the use of organic fertilizers can improve chemical properties of soil and reduce production costs. The objective of this study was to evaluate the effect of different fertilization sources on the chemical properties of soil under cassava cultivation. The experiment was conducted between 2017/2018 in the community of Boa Esperan&ccedil;a, Santar&eacute;m-PA using the cultivar Bem-te-vi, in the randomized block design with 4 treatments: T1 (without fertilization), T2 (fertilization NPK), T3 (organic fertilization with poultry manure), T4 (fertilization with cattle manure), with 5 replicates. The soil samples were analyzed for the contents K+, Ca&sup2;+, pH in H2O and KCl, Al&sup3;+ and soil organic carbon content (TOC). The data were submitted to analysis of variance and the means were compared by the Tukey test at 5% probability, using the software MINITAB&copy; version 18. There were statistical differences between the treatments for all the chemical properties analyzed. The findings of the analysis were that fertilization with catle manure and NPK were the same and differed from the other treatments for the contents of K+, pH in H2O and KCl, for Ca&sup2;+ and TOC. The treatment without fertilization obtained the lowest values differing from the others, for Al&sup3;+. The source from NPK obtained the lowest content in the soil. The treatments with organic fertilizers had higher levels of the above nutrients in the soil. The chemical properties of the soil were altered from the different management systems for the cultivation of cassava.

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