The dynamics of phosphorus (P) in the environment is important for regulating nutrient cycles in natural and managed ecosystems and an integral part in assessing biological resilience against environmental change. Organic P (P_o) compounds play key roles in biological and ecosystems function in the terrestrial environment being critical to cell function, growth and reproduction.

Silicon (Si) application has improved yield and stress tolerance in sugarcane crops. In this respect, C:N:P stoichiometry makes it possible to identify flows and interaction between elements in plants and their relationship with growth. However, few studies have investigated the influence of Si on physiological variables and C:N:P stoichiometry in sugarcane. As such, this study aimed to assess the effect of increasing Si concentrations on the growth and stoichiometric composition of sugarcane plants in the early growth stage. The experiment was conducted in pots, using four Si concentrations (0, 0.8, 1.6 and 3.2 mM). Biomass production, the concentration and accumulation of C, N, P and Si as well as the relationship between them were assessed. Silicon application increased biomass production, the rate of photosynthesis, instantaneous carboxylation efficiency and C, N, P and Si accumulation, in addition to altering stoichiometric ratios (C:N, C:P, N:P and C:Si) in different parts of the plants. The decline in C concentration associated with greater N and P absorption indicates that Si favoured physiological processes, which is reflected in biomass production. Our results demonstrate that Si supply improved carbon use efficiency, directly influencing sugarcane yield as well as C and nutrient cycling.

Silicon (Si) may be involved in the modification of C:N:P stoichiometry and in physiological processes, increasing sorghum growth and grain production. The objective was to evaluate the effect of Si supply on C:N:P:Si stoichiometry, physiological response, growth, and grain production of sorghum. The experiment was carried out in pots with four concentrations of Si: 0; 1.2; 2.4; and 3.6 mmol L⁻¹in a completely randomized design, with six replicates. Physiological attributes and dark green color index were measured and grain and biomass production were determined. Posteriorly, the plant material was ground to determine silicon (Si), carbon (C), nitrogen (N), and phosphorus (P) contents in order to analyze C:N:P:Si stoichiometry. C:Si and C:N ratios decreased at all Si concentrations applied (1.2, 2.4, and 3.6 mmol L⁻¹) and in all plant parts studied, being lower at 3.6 mmol L⁻¹. The lowest C:P ratios of leaves and roots were observed at 3.6 mmol L⁻¹Si and the lowest C:P ratio of stems was observed at 1.2 mmol L⁻¹Si. Si concentrations were not significant for the N:P ratio of leaves. The highest N:P ratio of stems was observed at 3.6 mmol L⁻¹, while the lowest N:P ratio of roots was observed at 2.4 and 3.6 mmol L⁻¹. Regardless of photosynthetic parameters, the application of 1.2 mmol L⁻¹Si enhanced photosynthetic rate. The application of 2.4 and 3.6 mmol L⁻¹enhanced stomatal conductance and dark green color index. The mass of 1000 grains was not influenced by Si applications, while Si applications at all concentrations studied (1.2, 2.4, and 3.6 mmol L⁻¹) enhanced shoot and total dry matter, not affecting root dry matter and grain production. In conclusion, Si supply modifies C:N:P:Si stoichiometry and increases physiologic parameters, growth, development, and grain production in sorghum.

A ureia é o principal fertilizante nitrogenado utilizado na adubação de cobertura no milho; no entanto, apresenta elevada suscetibilidade às perdas de N por volatilização de amônia. Uma alternativa é o tratamento da ureia com inibidor de urease ou revestimento com camadas de polímeros, classificados como fertilizantes nitrogenados de eficiência aumentada. Neste contexto, o presente trabalho objetivou avaliar o efeito da aplicação de doses de nitrogênio na forma de fertilizantes nitrogenados de eficiência aumentada e ureia em cobertura na cultura do milho. Utilizou-se o delineamento em blocos casualizados em esquema fatorial 3 x 4 + 1. As fontes utilizadas foram: ureia comum; ureia tratada com inibidor de urease e ureia revestida com polímeros testados nas doses de 32,5, 65, 130 e 260 kg ha-1 de N. A massa de cem grãos e a massa seca de parte aérea de plantas aumentaram de forma linear com as doses de N. O teor de nitrogênio na folha e a produtividade de milho foram superiores quando se utilizou ureia tratada com inibidor de urease ou revestida com polímeros, principalmente nas doses de 130 e 260 kg ha-1 de N. Neste sentido, a utilização de fertilizantes nitrogenados de eficiência aumentada não apenas aumentou mas também melhorou o suprimento de N para o milho aumentando ainda a produtividade de grãos.

Nitrogen deficiency and toxicity, primarily in its ammonium form (NH₄⁺), can suppress plant growth and development. The use of silicon (Si) or salicylic acid (SA) may be an alternative to minimize the harmful effects of nutrient imbalances caused by NH₄⁺, thereby improving the photosynthetic efficiency of plants. The aim of the present study was to assess the action of fertigation-applied Si and SA foliar spraying in mitigating NH₄⁺ toxicity and deficiency in eucalyptus clonal seedlings. Two experiments were performed with eucalyptus clonal seedlings (Eucalyptus urophylla x Eucalyptus grandis), in a greenhouse. Both were carried out using a 4x2 factorial design and four concentrations of NH₄⁺ (5, 15, 30 and 60 mmol L^-1), in the absence and presence of Si (2 mmol L^-1), in experiment I; or with and without SA foliar application (10⁻² mmol L^-1), in experiment II, with six repetitions. Nitrogen content rose as a result of increasing N-NH₄⁺ concentration in the nutrient solution, and Si supplied via the nutrient solution was efficient in increasing the Si content in eucalyptus seedlings. The rise in N-NH₄⁺ concentration favored the maintenance of the photosynthetic apparatus, but high N-NH₄⁺ concentration increased energy loss through fluorescence and decreased the efficiency of photosystem II. The addition of Si to the nutrient solution proved to be beneficial to the photosynthetic apparatus by decreasing F₀ at 15 and 30 mmol L^-1 of NH₄⁺; and F_m at all NH₄⁺ concentrations studied. In addition, the beneficial element also increases F_v/F_m at all NH₄⁺ concentrations studied. SA foliar application was also efficient in reducing photosynthetic energy losses by decreasing F₀ and F_m at all NH₄⁺ concentrations studied. However, SA only increased the F_v/F_m at the high concentrations studied (30 and 60 mmol L^-1 of NH₄⁺). Nitrogen disorder by deficiency or N-NH₄⁺ toxicity reduced shoot dry mass production. The addition of Si to the nutrient solution and SA foliar application increased shoot dry mass production at all N-NH₄⁺ concentrations studied, and benefitted the photosynthetic apparatus by decreasing fluorescence and improving the quantum efficiency of photosystem II as well as dry mass production.