Understanding the efficacy of alternative phosphorus (P) sources in tropical soils is crucial for sustainable farming, addressing resource constraints, mitigating environmental impact, improving crop productivity, and optimizing soil-specific solutions. While the topic holds great importance, current literature falls short in providing thorough, region-specific studies on the effectiveness of alternative P sources in Brazilian tropical soils for maize cultivation. Our aim was to assess the agronomic efficiency of alternative P sources concerning maize crop (Zea mays L.) attributes, including height, shoot dry weight, stem diameter, and nutrient accumulation, across five Brazilian tropical soils. In greenhouse conditions, we carried out a randomized complete block design, investigating two factors (soil type and P sources), evaluating five tropical soils with varying clay contents and three alternative sources of P, as well as a commercial source and a control group. We evaluated maize crop attributes such as height, dry weight biomass, and nutrient accumulation, P availability and agronomic efficiency. Our results showed that, although triple superphosphate (TSP) exhibited greater values than alternative P sources (precipitated phosphorus 1, precipitated phosphorus 2 and reactive phosphate) for maize crop attributes (e.g., height, stem diameter, shoot dry weight and phosphorus, nitrogen, sulfur, calcium and magnesium accumulation). For instance, PP1 source increased nutrient accumulation for phosphorus (P), nitrogen (N), and sulfur (S) by 37.05% and 75.98% (P), 34.39% and 72.07% (N), and 41.94% and 72.69% (S) in comparison to PP2 and RP, respectively. Additionally, PP1 substantially increased P availability in soils with high clay contents 15 days after planting (DAP), showing increases of 61.90%, 99.04%, and 38.09% greater than PP2, RP, and TSP. For Ca and Mg accumulation, the highest values were found in the _COxisol₂ soil when PP2 was applied, Ca = 44.31% and 69.48%; and Mg = 46.23 and 75.79%, greater than PP1 and RP, respectively. Finally, the highest values for relative agronomic efficiency were observed in _COxisol₂ when PP1 was applied. The precipitated phosphate sources (PP1 and PP2) exhibited a similar behavior to that of the commercial source (TSP), suggesting their potential use to reduce reliance on TSP fertilization, especially in soils with low clay contents. This study emphasized strategies for soil P management, aimed at assisting farmers in enhancing maize crop productivity while simultaneously addressing the effectiveness of alternative P sources of reduced costs.

The objective of this research was to evaluate the effects of potassium rates and water stress levels on the growth of maize (Zea mays, L.) plants. A pot (40 dm³) experiment was carried out using a Terra Roxa Estruturada Latossólica, an Alfisol intergrade to Oxisol, clayey loam soil, in Botucatu - São Paulo, Brazil, from December 1994 to February 1995. The experimental design was a randomized block with a (2 x 3 x 5) factorial distribution of the treatments. Two potassium rates (35 and 130 mg dm-3, as KCl) and three water stress levels were studied: no water stress (S0), moderate (S1) and intense (S2) levels, from the 44th day after emergence. All pots were irrigated to maximum soil water potentials (-0,0106 MPa) when the soil water potentials reached -0,0232, -0,0484 and -1,5 MPa for the S0, S1 and S2 treatments, respectively. Plant growth was evaluated during five periods, being the first at 27 days after emergence and each 14 days thereafter. The osmotic adjustment in leaves was measured using the volume-pressure technique. The leaves exhibited osmotic adjustment to potassium levels under moderated water stress. There were no effects of applied water stress levels on the contents of K, Ca and Mg in the leaves; however, the highest rate of potassium promoted the highest concentration of this nutrient and the lowest of Ca and Mg for all periods. The water stress levels did not affect the leaf area; however, the highest water level in soil increased the dry matter of all the components and mainly of the whole plant, the latter being the best parameter to evaluate water deficits. Potassium increased the leaf area, but did not affect any of the studied physiological indices. Water stress increase led to a decrease of the specific leaf area, leaf area rate and leaf matter rate. Potassium did not improve plant growth with limited water supply. However, those plants best supplied with potassium showed the highest mass production, regardless of the applied water levels, suggesting improved crop production.Este trabalho teve por objetivo estudar o efeito de variações nas doses de potássio e nos níveis de estresse hídrico sobre o ajustamento osmótico e crescimento de plantas de milho (Zea mays L.). Para tanto, instalou-se um experimento em vasos que continham 40 dm³ de Terra Roxa Estruturada Latossólica textura média argilosa, em casa de vegetação telada do Departamento de Ciência do Solo, Campus de Botucatu, UNESP/SP, de dezembro de 1994 a fevereiro de 1995. O delineamento experimental utilizado foi o de blocos ao acaso em esquema fatorial (2 x 3 x 3). Os tratamentos consistiram da aplicação de duas doses (35 e 130 mg dm-3) de potássio na forma de KCl e três condições de estresse hídrico, sendo plantas sem estresse (S0) e plantas que sofreram estresse hídrico moderado (S1) ou intenso (S2), 44 dias após a emergência. O crescimento das plantas foi avaliado em três épocas, aos 55, 69 e 83 dias da emergência. Da análise geral dos resultados pôde-se inferir que as folhas das plantas de milho se ajustaram osmoticamente com relação as doses de potássio, em condições de estresse hídrico moderado. Não houve efeito dos estresses hídricos na acumulação de K, Ca e Mg nas folhas; no entanto, a maior dose de K aplicado ao solo proporcionou, em todas as épocas, maior teor deste nutriente e menores de Ca e de Mg nas folhas. Os níveis de estresse utilizados não influíram na área foliar, mas o maior teor de água no solo aumentou a produção de matéria seca das partes e, principalmente, da planta toda, mostrando ser esta última a melhor característica para avaliação do déficit de água na planta. A maior dose de K proporcionou maior área foliar e produção de matéria seca às partes e à planta toda; no entanto, não influenciou o comportamento de nenhum índice fisiológico estudado. O maior teor de água no solo mostrou menores valores de área foliar específica (AFE), razão de área foliar (RAF) e razão de massa foliar (RMF). A adição de potássio não melhorou o crescimento da cultura, quando o fornecimento de água foi limitado. No entanto, as plantas mais bem nutridas em potássio produziram mais massa, independentemente dos níveis de água utilizados, indicando melhor produção de matéria seca destas plantas

Aluminum (Al) toxicity is a major constraint on crop growth and productivity in acidic soils, affecting root development, nutrient uptake, and photosynthetic performance. The use of Si is a promising strategy to overcome the adverse effects of Al toxicity on species of agronomic interest. Between 2020 and 2026, 15 studies across nine species consistently demonstrated that silicon mitigated aluminum toxicity, regardless of their classification as silicon accumulators. In plants, Si mitigates Al toxicity through a combination of physical, chemical, and biochemical mechanisms that operate simultaneously. In the rhizosphere, Si interacts directly with Al³⁺ ions, favoring the formation of hydroxyaluminosilicates (HASs), which reduces the bioavailable fraction of Al. Evidence indicates that solution pH is a critical factor governing HAS formation, with minimal attenuation of Al toxicity observed at pH values below 4.5. Within the plant, Si modulates the antioxidant defense system by enhancing the activity of enzymes such as catalase, peroxidase, and ascorbate peroxidase, thereby reducing oxidative stress typically triggered by Al toxicity. Moreover, Si influences the biosynthesis of lignin and phenolic compounds with Al-chelating capacity, contributing to detoxification at the cellular level. In soybean and rice, Si supply substantially reduced Al deposition in the root apical cell wall, with decreases of approximately 52% and 41.3%, respectively. This reduction was consistently associated with improved root elongation, maintenance of root structural integrity, mitigation of cellular deformation, and preservation of root thickness and vascular organization. Although these mechanisms have been described, a comprehensive synthesis of studies published from 2020 to 2026 has been lacking, particularly regarding the integration of in-plant processes and species-specific responses. This review fills this gap by critically examining recent findings, highlighting the multifaceted role of Si in alleviating Al stress, and discussing implications for agronomic applications in acidic soils. Collectively, the evidence underscores Si as an effective tool to enhance plant tolerance to Al; however, most available evidence is derived from early plant developmental stages and hydroponic or highly controlled systems, which limits the direct extrapolation of these findings to soil and field conditions. Future advances will require studies under soil environments, accounting for species-specific responses, soil properties, management systems, and plant developmental stages.

Responses to phosphate fertilizing by vernalized garlic (Allium sativum, variety Roxo Perola de Caçador) were studied. To determine the calibration curve for phosphorus extracted with ion exchange resin, five soils of different textural groups, with and without organic fertilizer, were utilized. Two experiments, placed in 16 L pots, were carried out under greenhouse conditions, in the county of Botucatu, State of São Paulo, Brazil, from May to October, 1995 and 1996. Each of these experiments consisted of five soils at six levels of phosphorus (0, 50, 100, 200, 400, and 800 mg dm-3 of P). Organic fertilizer was applied only in the first year, at a rate of 40 t ha-1 of bovine decomposed manure. The application of organic matter made it difficult to discriminate the lower levels of applied P. High levels of phosphorus increased the chlorophyll, N, P, K, and Mn concentrations and reduced the Mg concentration in the leaves; P showed no antagonistic effects on the Zn absorption. The critical level of phosphorus, extracted with ion exchange resin, for the five soils was approximately 50 mg dm-3 of P, while the critical foliar concentration of phosphorus was 2.5 g kg-1 of P. Organic fertilizer may substitute phosphate fertilization, in the dosage recommended by the State of São Paulo, for vernalized garlic crop.Estudaram-se respostas à adubação fosfatada pelo alho vernalizado cv. Roxo Pérola de Caçador em cinco solos com diferentes classes texturais, com e sem adubação orgânica, visando contribuir para o estabelecimento de curva de calibração para fósforo extraído por resina de troca iônica. Foram instalados dois experimentos entre maio e outubro de 1995 e 1996, em vasos (16 L), em casa de vegetação telada do Departamento de Ciência do Solo da Faculdade de Ciências Agronômicas/UNESP, município de Botucatu (SP). Cada experimento constituiu um fatorial com cinco solos e seis doses de fósforo (original, 50, 100, 200, 400 e 800 mg dm-3 de P). A adubação orgânica foi aplicada apenas no primeiro ano, na dosagem de 40 t ha-1 de esterco bovino decomposto. Verificou-se que a aplicação de matéria orgânica dificultou a discriminação dos níveis de fósforo extraído pela resina entre os tratamentos com menores doses de adubação fosfatada. A elevação nos níveis de fósforo aumentou a concentração de clorofila e de N, P, K e Mn e reduziu a concentração de Mg nas folhas; não foram observados efeitos antagônicos do P sobre a absorção de Zn. O nível crítico de fósforo extraído pela resina para os solos utilizados situou-se em torno de 50 mg dm-3 de P, enquanto a concentração foliar crítica de fósforo nas plantas de alho foi de 2,5 g kg-1 de P. A adubação orgânica, na dosagem recomendada para o estado de São Paulo, pode substituir a adubação fosfatada na cultura do alho vernalizado

The objective of this study was to evaluate the effects of acidity and availability of micronutrients on a sandy clay loam Oxisol grown with soybeans (summer) and black oat (autumn/winter), after long-term applications of biodigested sewage sludge (BS) and centrifuged sewage sludge (CS). The experiment was conducted in Botucatu, SP, Brazil, from 2002 to 2014, using a randomized block design, in 2×4 factorial scheme, with four repetitions. Treatments corresponded to six biennial applications of BS and CS at four doses: 0, 2, 4 and 8 Mg ha-1 (dry basis). Soil samples up to 0.60 m depth were taken after twelve years, and pH, potential acidity, exchangeable acidity and micronutrient contents were evaluated. The CS applications of 4 and 8 Mg ha-1 led to pH values within the recommended range up to depths of 0.10 and 0.20 m, respectively, whereas BS applications did not result in adequate pH values in any layer. The increased soil pH caused by CS applications resulted in a proportional reduction in soil potential acidity, whereas BS applications resulted in high value of potential acidity (70 mmolc dm-3) in all layers. The CS applications resulted in low Al3+ concentrations up to 0.20 m depth, whereas BS applications led to high Al3+ concentrations from the 0.05-0.10 m layer. The successive applications of both sludges resulted in Cu2+, Fe2+, Mn2+ and Zn2+ concentrations that exceeded the maximum values allowed in all soil layers. Low boron concentrations were found in the soil, and pH was the determinant factor for it.