Effects of Reduced and Conventional Tillage on Weed Communities: Results of a Long-Term Experiment in Southwestern Spain

G. PARDO,A.M.C. VERDÚ,F. PEREA,A. CIRUJEDA,M.T. MAS,J.M. URBANO

doi:10.1590/s0100-83582019370100152

G. PARDO, A.M.C. VERDÚ + Show 4 more

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https://doi.org/10.1590/s0100-83582019370100152

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Abstract

ABSTRACT: An important drawback in adopting minimum tillage (MT) and no-tillage (NT) techniques is the frequently observed weed shift promoting adapted species and achieving poorer weed control. These changes can be detected best with long-term experiments, and results might differ depending on soil characteristics and the local flora. The objectives of this work were to evaluate the effect of reduced tillage on weed seed distribution in the soil profile and to identify possible consequences on weed diversity on a long-term experiment maintained during 24 years in Seville (Spain) with three tillage systems: NT, MT and conventional tillage (CT) including moldboard plow on a vertisol. For this purpose, soil seedbanks at 0-8 cm and 8-16 cm depths were enumerated in autumn 2005 and in-field emerged plants in autumn 2005 and winter 2006. Shannon diversity index (H) and evenness (J’) were calculated for seedbank and aboveground weed communities. Total weed seed density was highest for NT and lowest for CT. Some big-seeded species, such as Chrozophora tinctorea L., showed highest seed density in CT. NT increased the relative density of Amaranthus blitoides S. Watson seeds in the seedbank and the abundance of emerged plants of Malva parviflora L., Anagallis arvensis L. and Picris echioides L. Overall, MT led to a less diverse seedbank in the 0-8 cm depth of soil than CT. The frequent drought-induced deep fractures in the expandable clay soil caused natural tillage, which probably resulted in fewer differences in weed seed and seedling densities among tillage treatments compared to what might be expected in other soil types.

Highlights

Production techniques like minimum tillage (MT) and non-tillage (NT) systems are alternatives to reduce soil losses (Brady and Weil, 2002), to maintain organic matter and moisture, and to provide stabilization of aggregates favoring water infiltration (Liebig et al, 2004; Thierfelder et al, 2015) versus conventional tillage (CT)
Nitrogen fertilizer and fuel were found to be the inputs with the highest reduction levels in the USA (Anderson, 2017)
Concerning weed control, fewer management options exist under MT and NT and, weed problems increase compared to CT for at least two reasons

Summary

Introduction

Production techniques like minimum tillage (MT) and non-tillage (NT) systems are alternatives to reduce soil losses (Brady and Weil, 2002), to maintain organic matter and moisture, and to provide stabilization of aggregates favoring water infiltration (Liebig et al, 2004; Thierfelder et al, 2015) versus conventional tillage (CT). Reduced tillage involves some disadvantages, such as higher surface compaction that can decrease water infiltration, new weed control problems, and major initial purchases of equipment for direct sowing, spraying weeds, and harvesting crops. MT and NT might promote infestations of species that emerge after partial burial or being left on the soil surface. Some examples of these species are grasses like Bromus diandrus Roth or Alopecurus myosuroides L. and the perennial species Cirsium arvense L., Convolvulus arvensis L., Cardaria draba (L.) Desv., Sonchus tenerrimus L. and Malva parviflora L. Some examples of these species are grasses like Bromus diandrus Roth or Alopecurus myosuroides L. and the perennial species Cirsium arvense L., Convolvulus arvensis L., Cardaria draba (L.) Desv., Sonchus tenerrimus L. and Malva parviflora L. (Mas and Verdú, 2003; Sans et al, 2011; Soane et al, 2012)

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