ABSTRACT Phosphorus (P) is one of the most difficult nutrients for plants to acquire because of its low content in the soil solution. Cassava (Manihot esculenta Crantz) has a thick and sparse absorbent root system; therefore, it is dependent on its association with arbuscular mycorrhizal fungi (AMF) for P acquisition from the soil. Thus, inoculation of cassava with AMF can improve the development of this root crop. This study evaluated the effects of soil disinfection (disinfected vs. natural) and the spore rates of Rhizophagus clarus inoculation (0, 50, 100 and 200 spores per plant) in greenhouse conditions on the initial growth, yield, P acquisition, and P use efficiency of cassava, as well as to evaluate the contribution of the native AMF to P acquisition from the soil. For cassava production in P-deficient soil, inoculation with Rhizophagus clarus significantly increased cassava growth, P uptake, and storage root yield only when the soil was disinfected. When the soil is not disinfected, native AMF contributes up to 86 % of the P taken up by cassava. However, high spore rates of Rhizophagus clarus in natural soil cause detrimental consequences for native AMF by reducing the colonization of the absorbent roots. Therefore, for cassava grown in natural soil under greenhouse conditions, a rate of 50 spores per plant of Rhizophagus clarus is sufficient to promote a 14.5 % increase in the yield of fresh storage roots. A management strategy that favors the native AMF multiplication in the soil is a potential strategy to improve P uptake and yield of cassava in P-deficient soils.

Em determinadas condições de relevo, do clima e de uso, com certa frequência pode acontecer acúmulo de sais nos solos, dando lugar à formação dos solos salinos e sódicos - também denominados de solos afetados por sais. A fim de orientar as práticas de manejo e uso das terras da região do Baixo Acaraú, CE, objetivou-se com o presente trabalho gerar um mapa de risco de salinização. Para obtenção das classes de vulnerabilidade, foram avaliados os temas pedologia, geologia, geomorfologia e uso e cobertura das terras e informações de declividade e altimetria, tratados em ambiente SIG com o método multicritério aditivo. Foram definidas quatro classes de risco de salinização: baixo, moderado, alto e altíssimo ou solos naturalmente salinos/sódicos. Foi constatado que 35,47 % da área corresponde à classe de baixo risco de salinização; 26,22 %, à de risco moderado; 8,23 %, à de risco alto; e 19,65 %, à de risco altíssimo.

Certain conditions of relief, climate and use can lead to the formation of saline and sodic soils, also called salt-affected soils. With a view to establish guidelines for management practices and land use in the region of Baixo Acaraú, Ceará, the purpose of this work was to generate a map of salinization risk. To classify levels of vulnerability, the pedology, geology, geomorphology and land use/cover were evaluated as well as slope altimetry information, treated in a GIS environment with an additive multi-criteria method. Four classes of salinization risk were defined: soils with naturally low, moderate, high, or very high salinity/sodicity. It was found that the risk of salinization was low in 35.47 % of the area, moderate in 26.22 %, high in 8.23 % and very high in 19.65 %.