Long‐term impact of legume‐based cropping with chemical and integrated fertilisation on viable weed seed density, diversity and community structure

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AbstractDominance, evenness and diversity of weeds in the seedbank have been recommended as potential indicators for monitoring the sustainability of cropping systems. We aimed to investigate viable seed density and diversity in soil after 13 years of diversified cropping and nutrient management practices. The long‐term field experiment comprised four cropping sequences: maize (Zea mays L.)–wheat (Triticum aestivum L.) (M‐W), maize–wheat–mungbean (Vigna radiata L.) (M‐W‐Mb), maize–wheat–maize–chickpea (Cicer arietinum L.) (M‐W‐M‐C) and pigeonpea (Cajanus cajan L.)–wheat (P‐W) in main plots and three nutrient management regimes: without fertilisation (CT), recommended inorganic fertilisers (RDF) and integrated nutrient management (INM) in subplots. The importance value index (IVI), the sum of relative frequency, density and abundance, was used to measure how dominant a species was in a given treatment. The M‐W rotation recorded a higher IVI of Phyllanthus niruri L. and Medicago denticulata L. compared with legume‐based cropping (M‐W‐Mb, M‐W‐M‐C and P‐W). INM also resulted in higher IVI of these species than RDF in the 0–15 cm soil layer. The P‐W rotation resulted in 33%–40% (at 0–7.5 cm), 16%–26% (at 7.5–15 cm) and 27%–36% (at 0–15 cm) higher seed density compared to the remaining rotations (expressed as the mean of other rotations). However, the sequence of seed density was INM = CT > RDF for the nutrient management. Weed species diversity (Shannon and richness indices) in the seedbank was higher in legume‐based cropping than the M‐W. The M‐W rotation also had higher ecological dominance than legume‐based rotations throughout the soil profile. Averaged across depths, RDF had 16% higher ecological dominance than the INM practice. Above‐ground weed density in wheat at harvest was significantly lower in M‐W‐Mb and M‐W‐M‐C than the M‐W rotation indicating that weed pressure and competition in wheat are reduced when systems were diversified with mungbean and chickpea. However, the P‐W rotation and INM can increase both weed seed density and species diversity compared with continuous cereal–cereal rotation (M‐W) and chemical fertilisation (RDF) in the long term. Thus, diversification of M‐W with legume (chickpea and mungbean) can be an important strategy to enhance species diversity vis‐à‐vis to reduce weed competition, herbicide inputs and avoiding the evolution of herbicide resistance.