Impacto de plantas de cobertura e da distribuição de chuvas sobre Scaptocoris castanea (Hemiptera: Cydnidae)

The objective of this work was to evaluate the population dynamics of the burrower bug (Scaptocoris castanea) in an area with cotton (Gossypium hirsutum) cultivated after cover crops. The insects were counted in soil samples collected at 0–40 cm depth. Insect incidence was documented in 18 cover crops, alone or intercropped, in each plant stage. Rainfall distribution was compared with fluctuations in the burrower bug population. Crotalaria species have a suppressive effect on the insect population, whereas some grass species favor its increase. Rainfall distribution directly influences the insect population.O objetivo deste trabalho foi avaliar a dinâmica populacional do percevejo-castanho (Scaptocoris castanea) em área com algodão (Gossypium hirsutum) cultivado após plantas de cobertura. Os insetos foram contados em amostras de solo coletadas a 0–40 cm de profundidade. A incidência de insetos foi documentada em 18 espécies de cobertura, isoladas ou consorciadas, em cada estágio da planta. A distribuição das chuvas foi comparada com a flutuação populacional do inseto. Espécies de crotalária apresentam efeito supressivo sobre a população do percevejo-castanho, enquanto algumas espécies de gramíneas favorecem o seu aumento. A distribuição das chuvas influencia diretamente a população de insetos

DRY MATTER DECOMPOSITION OF COVER CROPS IN A NO-TILLAGE COTTON SYSTEM

<div><p>ABSTRACT No-tillage cotton systems require soil coverage with cover crop residue for a longer time due to the late cycle of cotton. However, decomposition rates may vary between cover crops, and the adjustment of models to describe it is critical to no-tillage cotton management. Two non-linear regression models, exponential (EM) and Michaelis-Menten (MM), were adjusted to dry matter decomposition of cover crops in a cotton no-tillage system, in Brazil. Three field trials were performed in 2012 for the cover crops Urochloa ruziziensis (brachiaria), Pennisetum glaucum (pearl millet), and Cajanus cajan (pigeon pea). Samples of cover crop were collected at 20, 50, 70, 110, 140, and 170 days after sowing upland cotton to measure dry matter decomposition. MM showed better adjustment than EM for all cover crops. The estimations of half-life parameters were different between the cover crops, suggesting that each cover crop has its own rate of decomposition. For pearl millet, brachiaria, and pigeon pea, the half-life estimation by exponential model was over the MM in 9, 12, and 12 days.</p></div