Acúmulo de matéria seca e macronutrientes por plantas de Merremia aegyptia

Abstract

RESUMO -Um experimento em casa de vegetação foi conduzido entre janeiro e junho de 2008, na FCAV/UNESP, Brasil, objetivando estudar a produção de massa seca, a marcha de absorção e o acúmulo de macronutrientes por Merremia aegyptia, uma importante planta daninha em culturas anuais e perenes no Brasil. As plantas foram cultivadas em vasos de 7 L com substrato de areia, que foram irrigados diariamente com solução nutritiva de Hoagland & Arnon. Os tratamentos corresponderam às épocas de avaliação, em intervalos de 14 dias, iniciando-se 21 dias após a emergência (DAE). Em cada avaliação, as plantas de quatro vasos foram analisadas quanto à produção de massa seca e ao conteúdo de macronutrientes. M. aegyptia apresentou pequeno acúmulo de massa seca e de macronutrientes no início da fase experimental, os quais foram intensificados após 49 DAE. As folhas foram as principais estruturas acumuladoras de massa seca na primeira metade do ciclo de M. aegyptia, enquanto os caules o foram na segunda metade. N e K foram os macronutrientes mais acumulados em plantas de M. aegyptia. O período de máximo acúmulo teórico de massa seca e macronutrientes por M. aegyptia ocorreu entre 146 e 160 DAE.Palavras-chave: plantas daninhas, Convolvulacea, jitirana, crescimento, nutrição.ABSTRACT -A greenhouse experiment was carried out from January to June 2008 at FCAV/ UNESP, Brazil, to study dry mass production, absorption rate and macronutrient accumulation in Merremia aegyptia, an important weed in annual and perennial crops in Brazil. The plants were grown in seven liter pots with sand substrate and irrigated with Hoagland and Arnon nutrient solution. The treatments corresponded to the evaluation times, at 14 day intervals, beginning at 21 days after emergence (DAE). Plants of four pots were analyzed for growth and mineral nutrition. M. aegyptia showed small dry mass and macronutrient accumulation at the beginning of the experimental stage, which was intensified after 49 DAE. The main structures accumulating dry mass in the first half-stage were the leaves, and in the second half-stage, the stems. N and K accumulated more in M. aegyptia plants. The maximum theoretical period of dry mass and macronutrients for M. aegyptia occurred between 146 and 160 DAE.

Accumulation of dry mass and macronutrients by sourgrass plants

“…Greater dry mass accumulation by stems rather than leaves after the middle third of the experimental stage, higher requirement of macronutrients at the beginning of the experimental stage, K and N as the macronutrients required at higher levels, and Mg and S as the macronutrients required as lower levels in sourgrass plants were similar to results observed for American black nightshade (Bianco et al, 2010), ivyleaf morningglory (Guzzo et al, 2010), and hairy woodrose (Martins et al, 2010). However, different behavior was observed for the time of flowering, the PtMAXdm, the PtMAXmn, and the total amount of accumulation of dry mass and macronutrients.…”

“…Increasing dry mass allocation was provided by greater accumulation by stems rather than leaves, since the percentage of the dry mass accumulation by leaves, main organs producing photoassimilates, rapidly reduced after 35 DAE in comparison with other plant parts. That behavior has been observed for all weeds previously studied and it is attributed to a better plant fixation in the substrate, increasing the contact of nutrients by root interception and causing their rapid accumulation by roots (Bianco et al, 2010;Guzzo et al, 2010;Martins et al, 2010).…”

“…Hairy woodrose was also observed requiring great amounts of macronutrients for plant growing (Martins et al, 2010), but it was not verified for ivyleaf morningglory plants (Guzzo et al, 2010). Apart from interfering indirectly with crop productivity due to block the reel of the combine in mechanical harvesting (Moro et al, 2011), climbing plants, such as hairy woodrose and ivyleaf morningglory, can also interfere directly with crop productivity by competition for environmental resources.…”

“…Considering that the period of higher competition of weeds with the most annual crops is close to 77 DAE (Bianco et al, 2010;Guzzo et al, 2010;Martins et al, 2010), a time for intense increasing in the extraction of the nutrients studied, sourgrass plants showed average accumulation of 15.5 g of dry mass, 58.5 mg of N, 7.6 mg of P, 89.2 mg of K, 14.4 mg of Ca, 10.8 mg of Mg, and 3.6 mg of S by a single plant, at this time of evaluation. In function of the high reproductive capacity by seeds and rhizomes and the perennial life Accumulation of dry mass and macronutrients by ... cycle, sourgrass plants can be present in agricultural fields for a long time if not controlled, reducing the amount of nutrients available for crop growing and causing important biotic pressure on both annual and perennial crops.…”

“…There are many papers on nutritional requirements of weeds emphasizing the importance of this type of research, such as the recent ones published by Bianco et al (2010) on Solanum americanum Mill. (American black nightshade), Guzzo et al (2010) on Ipomoea hederifolia L. (ivyleaf morningglory), Martins et al (2010) on Merremia aegyptia (L.) Urban. (hairy woodrose), and others.…”