عنوان مقاله [English]
Introduction: Potato is a cool-season vegetable that ranks with wheat and rice as one of the most important staple crops in the human diet around the world. Weed control is important in potato production management, because without doing it potato harvest would not be cost- effective. Metribuzin (4-amino-6-tert butyl-3-methylthio-1, 2, 4-triazin-5-one), a triazine, is used as a selective herbicides for control of annuals grasses and broadleaf weeds inpotato. Its herbicide efficiency and its relatively low toxicity are such that it is widely used around the world. Replacing metribuzin with other herbicide that have the greatest effect on weed control in potato seems unlikely. The persistence of metribuzin in soil is defined as the period or extension of time in which it remains active. Knowing the case of herbicides is particularly important because, on one hand, it determines the period of time in which weeds can be controlled, and on the other, it is related to the later phytotoxic effects which can damage the subsequent crops. In order to understand about affiance of this herbicide in potato fields, researches on metribuzin toxicity in common lamb’squarters in soils with different utilizations are essential.
Material and Methods: This experiment was conducted to study the effect of soil characteristics and utilization history of metribuzin on its efficiency to common lamb’squarters control as a factorial on the base of randomized complete blocks design with three replications in green house of Institue of Plant Protection in 2012. First factor was soil type in six levels (Hamedan with 15 years and without utilization history, Jiroft with 15 years and without utilization history, Isfahan with 2 years utilization history and Mashhad with 3 years utilization history) and second factor was concentration of metribuzin in six levels (included 0, 100, 300, 700 and 1000 g ai h-1). Soil samples were collected from 0-15 cm depth. Before cultivating, the pots with mentioned soils were treated with metribuzin. Each sample was thoroughly mixed to allow a homogeneous distribution. Non-sprayed samples were used as controls. Common lamb’squarters seeds were planted in pots and the soil in each pot was watered as mist. After emergence, the seedlings were thinned to two per pot. Harvesting weeds were done four weeks after sowing. Then, dry weight and the length of shoot and root were measured. All data were subjected to analysis of variance and means were compared at the 5% level of significance. The classical bioassay, often used to quantify the amount of herbicide in soil, employs a single “standard” dose-response curve. This standard curve show the plant response to different herbicide concentrations and report information of different concepts related to herbicide efficacy, such as selectivity, tolerance and resistance. A typical dose-response curve is sigmoid in shape. One example of such a curve is the loglogistic curve. The data were expressed as a percentage of the untreated control and dose- response curves were drawn.
Results: According to results, more common lamb’squarters was controlled due to increase of herbicide dose. But the effects of metribuzin residue were decreased by increase of amounts of clay, organic matter and utilization history. The amount of herbicide required to reduce the growth of weed by 50% (GR₅₀) when compared with the control was determined for each soil. In the soils with higher organic matter GR₅₀ were increased. The highest and lowest damage to common lamb’squarters was observed in soils of Jiroft without utilization history and Hamedan with 15 years utilization history, respectively So in the soil with long utilization history of metribuzin, common lamb’squarters control was greatly reduced due to the presence of microorganisms adapted to the herbicide and use of it to supply energy. The breakdown of herbicides by soil organisms known as microbes accounts for a large portion of herbicide degradation in soil. Certain bacteria, fungi, and algae use herbicide as a food source. Microbes are herbicide-specific and their population in the soil is related to the amount of herbicide can lead to increased microbe populations and a shorter duration of effective weed control. Organic matter provides excellent habitat for microbes. The adsorption degree of this herbicide is positively correlated with organic matter content and negatively with their persistence. In these situations for controlling this weed higher concentration of metribuzin must be used.