Understanding mechanisms of reduced annual weed emergence in alfalfa

Abstract

Field experiments were carried out at the Facultad de Agronomía, Universidad de Buenos Aires, Argentina (34°25′S, 58°25′W), to evaluate the possibility of reducing weed seedling emergence through the use of alfalfa cultivars with low levels of winter dormancy and by increasing plant density from 200 to 400 plants m−2. It was hypothesized that these treatments would alter the temperature regime and the red (R)–far-red (FR) ratio of radiation to which seeds were exposed. Responses to management treatments were recorded for bull thistle, cotton thistle, plumeless thistle, tall rocket, mustard, curly dock, and pigweed. During the alfalfa establishment year, pigweed and curly dock emergence was reduced by the nondormant cultivar established at high density. This reduction disappeared when soil beneath the canopy was fitted with heaters that mimicked bare-soil temperatures. Crop canopy presence during the establishment year was not effective in reducing mustard, cotton thistle, bull thistle, plumeless thistle, and tall rocket emergence. During the second and third years after crop establishment, the canopy of the nondormant alfalfa cultivar was effective in reducing germination of weed seeds placed on the soil surface during fall and winter. In contrast, the winter-dormant cultivar allowed the establishment of weeds during the winter period. These reductions in weed emergence were associated with a modification in the R–FR ratio perceived by the seeds located at the soil surface and could largely be removed by using FR filters to increase the R–FR ratio. These results suggest that the selection of a nondormant cultivar combined with an increase in plant density could effectively reduce weed populations in alfalfa.

Winter Cover Crop Growth and Weed Suppression on the Central Coast of California1

“…Most of the weeds emerged in the first 50 DAP, which may explain why cover crop treatment did not affect weed emergence. Crop effects on weed emergence are more common in late-emerging weed species (Huarte and Arnold 2003). There were 72 and 70% fewer live weeds under the cover crops in February than January of yr 1 and 2, respectively (data not shown), indicating that most emerged weeds had senesced before the end of the cover crop season.…”

Contrasting weed species composition in perennial alfalfas and six annual crops: implications for integrated weed management

“…In perennial crops, soil characteristics (organic matter, humidity, nutrients) and microclimatic conditions (temperature, light quantity and quality) relevant to weeds may be different to annual crops (Entz et al, 2002). Therefore, some weed species may not be able to germinate without soil disturbance (Huarte and Arnold, 2003), and a delayed nitrogen availability in legume-based cropping systems (in contrast to mineral N fertilisation) may favour species with larger seeds over smaller seeds (Liebman and Davis, 2000). Finally, the absence of soil tillage and the permanent vegetation cover may favour weed seed decay or seed predation by animals (Westerman et al, 2005).…”

Linking Climatic Variability with Spatial Performance in Two Varieties of Quinoa Distributed in a Semi-Arid Zone

“…For instance, [21] demonstrated negative impacts of climate variability on production in many crops, where the temperature variability increased the risks to yield, as shown via computer simulation and experimental studies. On the other hand, it has been reported that thermal oscillation may reduce both photosynthesis parameters and survival percentage, affecting the final performance of a determined crop [22]. Although both varieties decreased their performance in both field and greenhouse conditions when they were exposed to higher thermal amplitudes, they did so in different ways.…”