Silicon (Si) nanoparticles can attenuate nutritional disorders caused by phosphorus in forages through nutritional homeostasis. This paper aims to evaluate the effects of P deficiency and toxicity in Megathyrsus maximus cultivated in two types of soils and to verify whether Si application via fertigation can mitigate these imbalances. The following two experiments were carried out: cultivation of forage plants in pots with Entisol and Oxisol, in a 3 x 2 factorial design, with three nutritional levels of phosphorus (deficient, adequate, and excessive) and two Si concentrations in the irrigation water (0 and 1.5 mmol L-1). Height, number of tillers, rate of leaf senescence, dry matter production, C:N, C:Si, C:P, and N:P ratios; and C, P, and N use efficiencies were evaluated in two growth cycles. P imbalances hampered carbon assimilation, C:N:P homeostasis, and dry matter production. Nanosilica fertigation promoted silicon uptake, improving C:N:P homeostasis and nutritional efficiency in plants under P deficiency and toxicity. Leaf senescence showed a lower value with addition of Si in plants grown in Oxisol in the three nutritional states of P. Silicon attenuated the stress caused by P toxicity in Entisol and Oxisol, improving production in plants without nutritional stress in Oxisol. The supply of Si nanoparticles in the cultivation of grass forage can contribute to a more efficient and sustainable use of phosphorus in pastures.

Silicon (Si) nanoparticles can attenuate nutritional disorders caused by phosphorus in forages through nutritional homeostasis. This paper aims to evaluate the effects of P deficiency and toxicity in Megathyrsus maximus cultivated in two types of soils and to verify whether Si application via fertigation can mitigate these imbalances. The following two experiments were carried out: cultivation of forage plants in pots with Entisol and Oxisol, in a 3 × 2 factorial design, with three nutritional levels of phosphorus (deficient, adequate, and excessive) and two Si concentrations in the irrigation water (0 and 1.5 mmol L−1). Height, number of tillers, rate of leaf senescence, dry matter production, C:N, C:Si, C:P, and N:P ratios; and C, P, and N use efficiencies were evaluated in two growth cycles. P imbalances hampered carbon assimilation, C:N:P homeostasis, and dry matter production. Nanosilica fertigation promoted silicon uptake, improving C:N:P homeostasis and nutritional efficiency in plants under P deficiency and toxicity. Leaf senescence was reduced with addition of Si in plants grown in Oxisol in the three nutritional states of P. Silicon attenuated the stress caused by P toxicity in Entisol and Oxisol, improving production in plants without nutritional stress in Oxisol. The supply of Si nanoparticles in the cultivation of M. maximus can contribute to a more efficient and sustainable use of phosphorus in pastures.

In cultivated soils with pastures in different regions of the world, phosphorus (P) imbalances are recurrent. In addition to P deficiency, the occurrence of areas with excess P in the soil has increased, with damage to pasture production. This reality requires the search for thoughtful strategies such as the use of silicon (Si), which is an element known to attenuate stress in plants. However, the action of Si on morphogenetic and chemical characteristics of grasses forages cultivated in different soils is not known. Therefore, this study aimed to evaluate the effects of P deficiency and excess on morphogenetic and chemical parameters, and on the digestibility of Zuri guinea grass cultivated in Oxisol and Entisol, and to analyze whether fertirrigation with nanosilica can mitigate the damage caused by these nutritional stresses. P deficiency decreased tiller number and grass protein content, and increased lignin content, while P excess increased the percentage of dead material and lignin, and decreased the leaf:stem ratio of plants, and both stresses decreased dry matter (DM) production. Fertirrigation with Si promoted better tillering and protein in deficient plants. In the excess of P, Si reduced tiller mortality and the lignin content of the plants, increasing the leaf:stem ratio and DM production, also increasing the production of plants with P sufficiency, without affecting the digestibility of the grass. Thus, the perspective is that the use of Si can improve the growth and chemical characteristics of forage grasses under P stress, and optimize production in nourished adapted plants, confident for more sustainable pasture production.

This is an article published in open access under a Creative Commons license Soil bulk density is a measure used to diagnose compaction and consists of collecting undisturbed samples using a 100 cm³ metal cylinder with Uhland auger (Teixeira, Donagema, Fontana & Teixeira, 2017). Pires, Rosa & Timm, (2011) point out that sampling is the most critical operation due to soil heterogeneity and careful not to neglect the results by compressing the sample and affecting its structure, arrangement and volume.

A irrigação é atualmente o maior consumidor de água no Brasil, sendo responsável por 52% do total de água retirada. Além disso, a perspectiva brasileira é de um aumento em 24% no consumo hídrico global até 2030 (ANA, 2018), o que agravará a disputa por este recurso, forçando ao uso de técnicas e tecnologias mais eficientes. Na busca de melhor aproveitamento da água na agricultura irrigada, devese utilizar os sistemas mais adequados às condições socioeconômicas locais, além de proceder a um manejo cuidadoso da irrigação. No caso da irrigação por aspersão, o conhecimento dos valores da uniformidade de distribuição de água é imprescindível na definição da lâmina bruta a ser aplicada e no tempo necessário para operação otimizada do sistema (COELHO & SILVA, 2013), influenciando os custos com energia e da própria água consumida, tendo importância maior ainda onde a conservação da água é enfatizada (FISCHER & WALLENDER, 1988). Alguns fabricantes de aspersores, cientes da importância da conservação da água, produzem seus emissores com mecanismos capazes de reduzir a vazão dos mesmos, o que proporciona, por exemplo, uma menor perda de água por escoamento superficial, mas não apresentam geralmente informações sobre a sua forma de distribuição de água.Assim, este trabalho objetivou avaliar a interferência de um mecanismo redutor de vazão de um sprayer de irrigação sobre a sua uniformidade de distribuição de água. MATERIAL E MÉTODOS:Os trabalhos foram realizados no laboratório de irrigação do IFRJ campus Pinheiral. Foi utilizado um sprayer (aspersor fixo) de irrigação, marca Fabrimar, modelo Sempre Verde, setorial de 90º, instalado a uma altura de 0,282 m. Este emissor possui um dispositivo de redução de vazão por meio de um parafuso que permite o ajuste de vazão desde a saída plena de água até seu total fechamento (Figuras 1a e 1b), tendo um ângulo de abertura total de aproximadamente 1100º. Avaliou-se, então, nas pressões de 150 kPa e 300 kPa, as características de distribuição de água. com o parafuso de regulagem de vazão ajustado para abertura plena (1100º), e aproximadas de 3/4 (825º), 1/2 (550º), 1/4 (275º), 1/8 (138º) e 1/16 (69º) da abertura total por meio do dispositivo mostrado na Figura 1c. Foram utilizados coletores de PVC com altura de 0,155 m e diâmetro de abertura de 0,098 m, dispostos em malha quadrada com 0,25 m de lado, em ensaios com uma hora de duração, e realizado o monitoramento das temperaturas do ar e da água, bem como da umidade relativa, conforme orientações apresentadas pela ABNT (2016).