Brazil stands out in grain production, being the world's second-largest soya bean producer and the largest in Latin America. The area occupied by leguminous in the 2018/2019 harvest was 36 million hectares (CONAB, 2019). The Cerrado biome occupies about 44% of the country's agricultural area, which is responsible for 60% of total soya bean production (DICKIE, Magno, Giampietro, & Dolginow, 2016). The advance of agriculture in this biome is growing, which tends to further increase the percentage of crop production. In the Cerrado, the volume and frequency of rainfall is often fluctuating and insufficient, reducing the chances of adequate supply of the crop's water demand (Goes, Rodrigues, Arf, Arruda, & Vilela, 2011; Tardin et al., 2013). Therefore, it is common in Cerrado the soya bean crops to be subjected to drought stress conditions in their early stages, which can affect the germination process. The severity of the drought stress effect on soya bean depends on the

RESUMO

Seeds of maize (Zea mays L.) and sorghum [Sorghum bicolor (L.) Moench.] were submitted to different osmotic potential levels induced by polyethylene glycol (PEG) with the objective of evaluating the effects of drought stress on seed germination and early seedling growth. Seeds were arranged in paper rolls and soaked in PEG solutions prepared with osmotic potentials 0.0 (control), -0.2, -0.4, and -0.8 MPa and kept into a seed germinator, at 25 °C for 18 days. A completely randomized design in a 2 × 4 factorial scheme with four replications of 50 seeds each was used. The results showed that by increasing of the osmotic potential level, germinated seed number, germination rate index, root and shoot length, shoot and root dry matter, and seedling vigor index (SVI) decreased, while mean germination time (MGT) and root: shoot ratio (RSR) increased in both crops. Additionally, the maize was more susceptible than sorghum to drought stress, with germination response declining more rapidly with decreasing osmotic potential. Sorghum crop tolerates water stress of up to -0.2 MPa, without reducing germination of the seeds; however, the growth of shoots and roots are inhibited. Drought stress limits the process of seed germination and early growth of maize seedlings.

A pesquisa sobre bactérias diazotróficas na cultura do milho tem demonstrado a necessidade de associar bactérias eficientes a genótipos promissores, os quais se beneficiariam dessa associação. Assim, conduziu-se um experimento em condições de campo, no município de Marechal Cândido Rondon (PR), com o objetivo de avaliar o comportamento de dois híbridos de milho à inoculação de Herbaspirillum seropedicae, sob diferentes níveis de nitrogênio. Utilizou-se o delineamento experimental de blocos ao acaso em esquema fatorial 2 x 2 x 3, com cinco repetições. Os tratamentos foram constituídos por dois híbridos (AS 1540 e AS 1560); ausência ou presença de inoculação com H. seropedicae, e três níveis de N em cobertura (0, 40 e 80 kg ha -1 ). Os dados obtidos evidenciaram que a inoculação de H. seropedicae não influenciou significativamente a produtividade dos dois híbridos de milho testados; contudo, verifica-se que o híbrido AS 1570 respondeu positivamente à inoculação com aumento de 8,6% na produção de grãos, e o híbrido AS 1540 foi afetado negativamente com uma redução na produtividade de 5,1%, evidenciando que os híbridos de milho testados apresentam resposta diferenciada à inoculação de H. seropedicae. As doses de N aplicadas em cobertura influenciaram significativamente a maioria das variáveis analisadas. Palavras-chave:Adubação nitrogenada, bactérias diazotróficas, fixação biológica de nitrogênio, promoção de crescimento, Zea maysMaize yield in response to Herbaspirillum seropedicae inoculation under different nitrogen levels ABSTRACTThe research on diazotrophic bacteria in maize has shown the need to associate effective bacteria to promising genotypes, which would benefit from this association. Thus, an experiment was conducted under field conditions in the municipality of Marechal Cândido Rondon-PR, Brazil, aiming at evaluating the performance of two maize hybrids with Herbaspirillum seropedicae inoculation under different nitrogen levels. The study was carried out in experimental design of randomized blocks in factorial 2 x 2 x 3 with five replications. The treatments consisted of two hybrids (AS 1540 and AS 1560); presence or absence of inoculation with H. seropedicae , and three levels of nitrogen in covering (0, 40 and 80 kg ha -1 ). The data obtained showed that H. seropedicae inoculation did not significantly influenced the productivity of the two tested maize hybrids; however, it is observed that the hybrid AS 1570 responded positively to inoculation with an 8.6% increase in grain production, and hybrid AS 1540 was negatively impacted by a yield reduction of 5.1%, showing that the hybrids tested had different responses to H. seropedicae inoculation. The doses of N applied in covering significantly influenced most of the variables.

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The efficiency of potassium (K) fertilizer use is important in sustainable agriculture and is affected by losses related to soil texture. However, there is no information on how much K is lost by leaching in tropical soil. The effects of rates of fertilizer‐K application on K dynamics and budget in a soil–plant system at depths up to 1 m were studied in Botucatu, São Paulo, Brazil, from 2000 to 2012; soil types were a sandy clay loam (250 g clay kg−1) and a clay soil (670 g clay kg−1) under no‐till management. The soils were fertilized annually with 0, 25, 50, 75, 100, 125 and 150 kg K ha−1. Annual applications of 50–75 kg K ha−1 to the sandy clay loam soil and 25–50 kg K ha−1 to the clay soil were sufficient to achieve a large grain yield and maintain soil exchangeable K in the soil profile. An annual application of up to 150 kg K ha−1 to clay soil does not result in a large amount of leaching below 1‐m depth. Non‐exchangeable K plays an important role in tropical cropping systems. The increase in rates of fertilizer‐K application intensifies losses by leaching below 1 m in sandy clay loam soil, which represents 16–52% of the K added as fertilizer. Therefore, because of the considerable leaching potential, splitting the applications of K is an important management strategy to minimize losses and improve the efficiency of K use in tropical soil with small clay contents. Highlights We investigated the effect of soil texture on K movement in the profile. Losses of K were estimated in a cropping system with cover crops. In tropical soil clay content plays an important role in the movement of K in the soil profile. In clay soil K losses are small, but can be up to 52% of the nutrient applied to sandy soil.

Aluminum (Al 3+) toxicity is a major limiting factor to crop productivity in acid soils. The effects of aluminum on root and shoot growth of physic nut (Jatropha curcas L.) young plants and, the uptake and distribution of phosphorus, calcium, magnesium and aluminum in the roots and shoots were investigated in the present study. Plants were grown in 2.5L pots in a greenhouse. After fourteen days of adaptation to nutrient solution, plants were exposed to Al concentrations of 0, 370, 740, 1,100 and 1,480 μmol L -1 , corresponding to an active Al 3+ solution of 13.3, 35.3, 90.0, 153.3 and 220.7 μmol L -1 , respectively. The dry matter partitioning between roots, stems and leaves, and the concentrations of P, Ca, Mg and Al in plant tissue, were measured after 75 days exposure to Al. The increasing level of Al 3+ activity in solution progressively decreased the growth of the shoot and root of physic nut plants, and at the two highest active Al 3+ levels, plants showed morphological abnormalities typical of the toxicity caused by this metal. Higher Al 3+ activity reduced P concentrations in leaves and Ca and Mg in leaves and roots of physic nut, demonstrating the effect of Al on the uptake, transport and use of these nutrients by plants. The Al accumulated preferentially in the roots of physic nut, whereas only a small amount was transported to shoots. Key words: Jatropha curcas, aluminum toxicity, aluminum tolerance Resumo

Seed size is an important indicator of physiological quality, since it may affect seed germination and seedling growth, especially under stress conditions. This study aimed to investigate the effects of seed size on germination and initial seedling growth, under salinity and water stress conditions. The treatments were arranged in a completely randomized design, in a 3 × 3 factorial scheme: three seed size classes (small, medium and large) and three stress treatments (control, saline or water stress), with four replicates. Water and salt stresses do not reduce the germination rate of medium and large seeds; however, the germination rate of small seeds is reduced under salt stress conditions. Drought stress drastically reduces the shoot growth of seedlings regardless of seed size, whereas root growth is higher in seedlings from medium and large seeds under water stress conditions. Under non-stressful environments, the use of large seeds is preferable, resulting in more vigorous seedlings with a greater dry matter accumulation. Medium-size seeds are more adapted to adverse environmental conditions and, therefore, should be used under conditions of water shortage and salt excess in the soil at sowing time. Seedlings are more tolerant to salinity than to water stress during the germination stage and initial growth under laboratory conditions.