Biological damage caused by macronutrient deficiency in watermelon plants is still not known, and may lead to nutritional disorders and alterations in absorption and utilization efficiencies, depending on the evaluated nutrient. In this context, the aim of the present study was to evaluate the growth and nutritional efficiency of watermelon plants grown under macronutrient deficiencies. The experiments were carried out in pots containing an aerated nutrient solution. Treatments consisted of the nutrient solution containing (control) or lacking nitrogen (LN), phosphorus (LP), potassium (LK), calcium (LCa), magnesium (LMg), and sulfur (LS), in a completely randomized design with three replications. At the end of the experiment with the onset of symptoms of deficiency, plant growth, green color index, nutrient accumulation, nutrient uptake, nutrient utilization efficiency, root density, and foliar deficiency symptoms were evaluated. P, K, Ca, Mg, and S deficiencies increased plant utilization efficiency and can potentiate watermelon development in environments deficient in these nutrients. The opposite was observed concerning nitrogen deficiency, because this condition induced greater biological damage, with low utilization efficiency, indicating the sensitivity of this species in low N conditions.

Alterações induzidas pela seca na absorção de nitrogênio, fósforo e potássio, e as relações com a tolerância da cana-de-açúcar ao deficit hídrico July, 19, 2016 and approved in November 23, 2016 ABSTRACTAlthough there are evidences that the proper supply of mineral nutrients to plants relieves water stress, little is known on the approach of how the drought affects the absorption and accumulation of nutrients by distinct sugar cane genotypes, or in different parts of a same plant. Thus, the objective of this study was to determine the content and accumulation of N, P and K in the aerial part of plant from three genotypes of sugar cane, submitted to three water potentials in the soil, and check the relationship of these variables with the tolerance of plants to prolonged drought. In order to access this objective, an experiment under greenhouse conditions, comprised by a fatorial 3 × 3, in a randomized block design, and four replicates was carried out. After 90 days from treatment imposition, the plant transpiration rate, plant dry mass, concentration of N, P and K were determined in leaves and culms, as well as in total plant shoot were measured. It was found that tolerance to drought in sugar cane is related to higher levels of N and K in the leaves and stems, and larger accumulations of K and P in the plant shoot. There is high positive correlations among accumulation of N, P and K in the plant shoot and dry matter production by plants submitted to drought. There are intermediate correlations among plant transpiration and nutrient uptake by plants under drought. Plants of the genotype SP81-3250 are more tolerante to prolonged drought, than the RB855453 and IACSP95-5000 plants.Index terms: Saccharum officinarum L.; water limitations; mineral nutrition; soil water potentials; plant growth. RESUMOEmbora existam evidências de que o adequado fornecimento de nutrientes minerais para plantas alivia o estresse hídrico, pouco se sabe sobre a abordagem de como a seca afeta a absorção e acumulação de nutrientes por distintos genótipos de cana-de-açúcar, ou por diferentes partes de uma mesma planta. Assim, o objetivo deste estudo foi determinar o teor e acúmulo de N, P e K na parte aérea da planta de três genótipos de cana-de-açúcar, submetidos a três potenciais hídricos do solo e verificar se existe relação dessas variáveis com a tolerância das plantas ao déficit hídrico prolongado. Para isso, foi realizado um experimento em casa de vegetação, em um esquema fatorial 3×3, em delineamento de blocos casualizados, com quatro repetições. Após 90 dias da imposição dos tratamentos, foi determinada a massa seca e a taxa de transpiração das plantas, a concentração de N, P e K nas folhas e colmos, além do acúmulo desses nutrientes na parte aérea das plantas. Verificou-se que a tolerância à seca em cana está relacionada com níveis mais altos de N e K nas folhas e caules e maiores acumulações de K e P na parte aérea das plantas. Existem fortes correlações positivas entre acúmulo de N, P e K na parte aérea das plantas e produção...

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