Seed germination of Bidens subalternans DC. exposed to different environmental factors.

Bidens subalternans DC. is a weed found in several tropical countries such as Brazil. Large number of produced seeds and easy dispersion favor the colonization of agricultural fields by this species. To know the factors that affect the germination of B. subalternans can help to understand its ecology, permitting to develop control strategies. Laboratory experiments were carried out to evaluate how the temperature, photoperiod, burial depth, water deficit, and salt stress affect the seed germination of B. subalternans. The means of the treatments of each experiment were shown in scatter plots with the bars indicating the least significant difference (LSD, p≤0.05). The results showed a germination percentage above 77% for a wide alternating temperature (15/20 C to 30/35 C night/day). The highest germination and uniformity occurred at 25/30°C night/day. Only 11% of the seeds germinated at a temperature of 35/40°C night/day. The deeper burial of seeds reduced their germination. Only 17% of the seeds germinated in darkness conditions. However, in constant light and 12 hours of light/dark conditions the germination percentage was over 96%, confirming the light dependence of the B. subalternans during germination. In constant light and 12 hours of light/dark, the germination was over 96%. B. subalternans seeds showed sensitivity to water and salt stress, and their germination was inhibited under a water potential of -0.4 MPa and 100.09 mM, respectively. The sensitivity of B. subalternans seeds to high temperatures, water stress, and salt stress explains the high frequency of this weed in south-central Brazil. The light and sowing depth showed that burial of seeds by mechanical control is a strategy to reduce the high infestation of B. subalternans.

Sorption and desorption of ametryn in different types of soils / Sorção e dessorção do ametryn em diferentes tipos de solos

Knowledge of factors related to the dynamics of herbicides in the environment is of fundamental importance to predicting the behavior of herbicides in soils with different attributes, to select appropriate dosages, as well as to avoid harmful effects on the environment and subsequent crops. The objective of this work was to evaluate the sorption and desorption of ametryn in seven soils with different attributes. Initially, the equilibrium time was determined by the "Batch Equilibrium". Then, it was performed the sorption test with different concentrations (0.5; 1; 2; 4; 8; 16; 24 and 32 mg L-1) of ametryn in 0.01 mol L-1CaCl2. 10 mL of these solutions were added to samples of 2.00 g of each soil, remaining under rotary shaking for 4 hours. After centrifugation and filtration, the ametryn concentration in the supernatant was determined by high-performance liquid chromatography. Desorption was evaluated using the tubes containing 16 mg L-1 prior to sorption testing. The results indicated that the sorption and desorption of ametryn depend on the physicochemical attributes of the soil. Sorption was higher in soils with high organic matter content and high ion exchange capacity, while desorption was inversely proportional to sorption.

O conhecimento dos fatores relacionados à dinâmica de herbicidas no ambiente é de fundamental importância para prever o comportamento de herbicidas em solos com diferentes atributos e para seleção de dosagens adequadas, bem como para evitar efeitos prejudiciais ao ambiente e às culturas subsequentes. O objetivo do trabalho foi avaliar a sorção e dessorção do ametryn em sete solos com diferentes atributos. Inicialmente, foi determinado o tempo de equilíbrio pelo método "Batch Equilibrium". Em seguida foi realizado o ensaio de sorção com diferentes concentrações (0,5; 1; 2; 4; 8; 16; 24 e 32 mg L-1) de ametryn em CaCl2 0,01 mol L-1. Foram adicionadas 10 mL destas soluções a amostras de 2,00 g de cada solo, permanecendo sob agitação rotatória por 4 horas. Após centrifugação e filtração, a concentração do ametryn no sobrenadante foi determinada por cromatografia líquida de alta eficiência. A dessorção foi avaliada utilizando os tubos que continham 16 mg L-1 antes do ensaio de sorção. Os resultados indicaram que a sorção e a dessorção do ametryn depende dos atributos físico-químicos do solo. A sorção foi maior em solos com alto teor matéria orgânica e alta capacidade de troca iônica, enquanto que a dessorção foi inversamente proporcional à sorção.

Accumulation of macronutrients in cowpea and weeds in competition and under soil water deficit / Acumulação de macronutrientes em feijão-caupi e plantas daninhas em competição e sob déficit hídrico no solo

The ability of a plant species to succeed in colonization of agroecosystem depends on its efficiency in the use of growth resources even in deficient conditions. The present study aimed to evaluate the effects of competition and water deficit in the soil on the accumulation of macronutrients of Vigna unguiculataL. Walp., Commelina benghalensis L. and Waltheria indica L. The study was conducted in a greenhouse, in randomized block design, with four replications. The treatments were arranged in a 5 × 2 factorial, with the first factor corresponding to types of interaction among species (V. unguiculata + C. benghalensis; V. unguiculata + W. indica; V. unguiculata in monoculture, C. benghalensis in monoculture and W. indica in monoculture), and the second of water regimes (irrigated and water deficit).The water deficit differently affects macronutrient content on the species, with decreased of K, Ca and Mg in cowpea, and N, P, K and Ca in W. indica. For C. benghalensis, the water deficit does not reduce the macronutrient contents on the plant. The competition between plants intensifies the effects of water deficit only on C. benghalensis, with a decreased on the content of all macronutrients studied. Under irrigated conditions, competition between plants was more damaging the weeds compared to cowpea. The C. benghalensis specie, free from interference, has a high potential for nutrient extraction under irrigated and water deficit regimes.

A capacidade de uma espécie vegetal para ter sucesso na colonização do agroecossistema depende da sua eficiência na utilização dos recursos de crescimento mesmo em condições deficientes. Objetivou-se avaliar os efeitos da competição e déficit hídrico no solo no conteúdo de macronutrientes de feijão-caupi (Vigna unguiculata L. Walp.), trapoeraba (Commelina benghalensis L.) e malva-branca (Waltheria indica L.). Foi conduzido estudo em casa de vegetação, em delineamento em blocos casualizado, com quatro repetições. Os tratamentos foram arranjados em fatorial 5 × 2, com o primeiro fator correspondente aos arranjos de competição entre as espécies (V. unguiculata + C. benghalensis; V. unguiculata + W. indica; V. unguiculataem monocultivo; C. benghalensis em monocultivo e W. indica em monocultivo), e o segundo dos regimes hídricos (irrigado e déficit hídrico). O déficit hídrico afeta de forma diferenciada o conteúdo de macronutrientes nas espécies, com redução de K, Ca e Mg no feijão-caupi, e N, P, K e Ca em W. indica. Para C. benghalensis, o déficit hídrico não reduz os conteúdos de macronutrientes na planta. A competição entre plantas intensifica os efeitos do déficit hídrico apenas em C. benghalensis, com redução do conteúdo de todos os macronutrientes estudados. Em condições irrigadas, a competição entre plantas foi mais prejudicial as plantas daninhas do que o feijão-caupi. Aespécie C. benghalensis, livre de interferência, apresenta elevado potencial de extração de nutrientes sob regimes irrigado e de déficit hídrico.