The search for high yield has identified ammonium toxicity as a problem in arable soils world wide. Ammonia toxicity can be suppressed by the use of silicon, but this fact still needs to be elucidated. Therefore, this review aimed to highlight the harmful effects of ammonium toxicity on model plants, and to determine the effects of Si on the mitigation of abiotic stress. Some plant species are considered as tolerant, and others as sensitive to high N concentrations. In sensitive plants, high ammonium concentrations may hinder the plant's development and even lead to the plant's death due to biochemical, physiological, and nutritional changes. Studies have demonstrated that silicon can mitigate or alleviate the deleterious effects caused by the toxic effect of NH 4 + . These findings were attributed to improvements in the physiological and nutritional parameters of plants. Given the importance of ionic balance between N forms for the plant's development, further studies must be performed to detect mechanisms promoted by Si to decrease or mitigate the harmful effects caused by excess ammonium in plants.Agronomy Journal. 2020;112:635-647. wileyonlinelibrary.com/journal/agj2 635

Gas exchange analysis is an important technique, as the reduction in yield may be related to the decreased photosynthetic activity, due to adverse climatic factors in the growing site. The hypothesis of this study was that contrasting soil water conditions result in different photosynthetic performance in soybean genotypes. Thus, our objective was to analyse the physiological capacity in soybean genotypes under field conditions with optimal soil moisture and under water deficit. The experimental design was random blocks with 10 genotypes (P1, P2, P3, P4, P5, P6, P7, P8, P9 and P10) and three replicates. Individual analysis of variance was performed in both environments (irrigated and rainfed), and a correlation network between the traits was generated. We measured the traits net photosynthesis, stomatal conductance, internal CO2 concentration, instant water‐use efficiency, instant carboxylation efficiency and grain yield. Stressed plants reduce stomatal conductance and transpiration, but increase the instant water‐use efficiency as a defence mechanism in sub‐optimal soil moisture conditions. The P6 genotype obtained better physiological capacity under irrigated conditions, while the P10 genotype showed the better performance under rainfed conditions, which makes it tolerant to water stress. Our findings can contribute to the genotype formation and parental choice steps in breeding programs aimed at obtaining both irrigation‐responsive and drought‐tolerant genotypes.

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This study evaluated the impact of macronutrient omission on nutritional disorders and the in vitro growth of Bletia catenulata. The experiment was performed in a growth room, with a controlled environment, in the biotechnology laboratory of the Campus of Chapadão do Sul (CPCS/UFMS). The experiment consisted of a completely randomized design, with seven treatments and four replications, corresponding to the following treatments: complete treatment (N, P, K, Ca, Mg, S, B, Mn, Zn, Cu, Fe, and Mo), nitrogen omission (–N), phosphorus omission (–P), potassium omission (–K), calcium omission (–Ca), magnesium omission (–Mg), and sulfur omission (–S) in B. catenulata. After detecting the symptoms, plant height, leaf area, dry weight, micronutrient content in the shoot, micronutrient accumulation in the shoot, and visual symptoms of nutritional deficiency were evaluated. The –N, –P, –Ca, and –Mg treatments hindered plant growth and dry weight yield. The deficiency of each nutrient resulted in morphological changes, which were verified by typical visual symptoms of nutritional disorder for each nutrient.

Avaliou-se neste estudo o efeito residual de plantas de cobertura na atividade das enzimas fosfatase ácida, arilsulfatase e beta-glucosidase e na respiração basal em solo cultivado com milho no Cerrado sul-mato-grossense. A fosfatase ácida, arilsufatase e beta-glucosidase variaram respectivamente de 755 a 1111; 74 a 131 e 167 a 299 µg p-nitrofenol g solo-1 h-1. As plantas de cobertura de espécies gramíneas proporcionaram maior atividade enzimática no solo quando comparada as demais. As coberturas Urochoa ruziziensis, sorgo e Urochoa brizanta promoveram os maiores valores nas atividades das enzimas do solo fosfatase ácida e arilsulfatase e os menores valores de respiração basal do solo. Para a enzima beta glucosidase a cobertura que proporcionou o maior valor de atividade foi o milheto, onde também foi observado maior valor de respiração do solo. De maneira geral, as menores atividades enzimáticas foram observadas em solo com as coberturas nabo forrageiro e crambe.