Abstract
In Europe, conservation agriculture (CA) is currently challenged by higher weed pressure, potential glyphosate ban and reduced crop yield. Based on preliminary results and a critical analysis, we provide insights on how to assess the effect of introducing different levels of tillage intensity, after a long-term CA sequence, on weed communities and crop yield. The experiment compared three types of fallow management (ploughing (CT), reduced tillage (RT), no-till with glyphosate (NT)) on four fields after 17 years of no-plough, which ended with 7 years of CA. The introduction of tillage proved to be a major driver of weed communities before weeding (density, richness and composition) in winter wheat. Weed density and species richness before weeding was greatest in RT, intermediate in CT and lowest in NT. The number of grains per ear and crop yield increased with tillage intensity (+11% for RT, +31% for CT). We provide avenues for future research through detailed methods and key references. Differences in winter wheat productivity were possibly related to enhanced soil structure and increased mineralisation of soil organic matter. Potential benefits of occasional ploughing will depend on the density and composition of the newly upwelled weed seedbank, which will need to be assessed before implementing tillage. From a multicriteria perspective, the long-term benefits associated with CA could largely exceed short-term yield increases associated with occasional tillage. Future studies will need to characterize the impact of occasional tillage operations on the long-term multiperformance of CA systems.
Highlights
Weed management in Conservation Agriculture (CA) relies on three fundamental pillars: diversified crop rotation, permanent soil cover and absence of soil disturbance [1]
In 2010, prior to the strict no-till phase, the weed seedbank assessment revealed that the superficial horizon was slightly more species rich (0–10 cm: 12 ± 2.7 species; 10–30 cm: 9.2 ± 3.1 species; paired t-test p-value < 0.01) and roughly four times more abundant (0–10 cm: 40,099 ± 17,043 seeds/m2 ; 10–30 cm: 11,069 ± 4956 seeds/m2 ; paired t-test p-value < 0.0001)
Weed seeds which were initially concentrated on the soil surface and in the superficial soil horizon were incorporated in the top soil—i.e., placed in more favourable conditions to germinate [9]
Summary
Weed management in Conservation Agriculture (CA) relies on three fundamental pillars: diversified crop rotation, permanent soil cover and absence of soil disturbance [1] This systemic vision of CA, thereby differing from conservation tillage [2], considers these three pillars as the immutable foundation required to provide the ecosystem services associated with CA (e.g., increase in soil biological activity and soil aggregate stability). A recent survey conducted by the ENDURE network (http://www.endure-network.eu/endure) in Europe [4] revealed occasional and recurrent uses of glyphosate, either in CA- or tillage-based systems. Such results encourage the investigation of alternative solutions along the substitution-to-redesign gradient [5]. The report indicated that a diversity of non-chemical alternatives to glyphosate existed, but that their effectiveness, cost and adoption implications were highly variable and/or difficult to quantify [4]
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