Abstract
We presumed that ecological engineering approaches such as pulse crop inclusion in crop rotation and integrated nutrient management (INM) would have higher weed seed density and diversity compared with continuous cereal-cereal rotation and chemical fertilization in long–run. Hence, we investigated the viable weed seed density and diversity in soil using the seedling emergence method in 0–7.5, 7.5–15, and 0–15 cm depth. Soil sampling was performed in 2016 after 13 years of field experimentation with same treatment combinations and layout on a sandy loam soil of Kanpur, India. The field experiment consisted of four crop rotations (since 2003): rice (Oryza sativa L.)–wheat (Triticum aestivum L.) (R–W), rice–wheat–mungbean [Vigna radiata (L.) R. Wilczek] (R–W–Mb), rice–wheat–rice–chickpea (Cicer arietinum L.) (two years rotation: R–W–R–C), rice–chickpea (R–C) and three nutrient management: control (without fertilization: CT), integrated nutrient management (INM), and recommended inorganic fertilization (RDF). Of the total 30 emerged weed species, 21 species were broad–leaved (70%), 8 grasses (26.7%), and 1 sedge (3.3%). Seed density of Leptochloa chinensis (L.) Nees was significantly higher in R–C(RDF) than R–W–Mb(RDF) and R–W(RDF). While, Lepidium didymum L., Dactyloctenium aegyptium (L.) Willd. and Anagallis arvensis L. were higher in R–W–Mb rotation over the R–W (P < 0.05). Pulse based cropping resulted in 6.1–13.2% higher (P < 0.05) seed density over R–W rotation at 0–7.5 cm depth, while, R–W rotation attributed 2.5–4.9% higher (P < 0.05) seed density than those of remaining rotations at 7.5–15 cm depth. In total depth (0–15 cm), total viable seed density followed the order of R–C = R–W–Mb (P > 0.05) > R–W–R–C (P < 0.05) > R–W (P < 0.05) and INM > RDF > CT (P < 0.05). Importance value index (IVI) of Cyperus rotundus L. and Medicago polymorpha L. was higher for R–W rotation than R–W–Mb, R–W–R–C and R–C (P < 0.05). Notably, pulse based cropping (R–W–Mb and R–C) had the lower ecological dominance and higher Shannon, Simpson, and richness indices than the R–W rotation at 0–7.5 cm and 0–15 cm layer, because of higher species diversity. RDF contained 31% higher ecological dominance than in the INM practice (P < 0.05). Principal component analysis showed that crop rotations and nutrient management mainly influenced the M. polymorpha, D. aegyptium, L. chinensis and L. didymum after 13 years. Medicago polymorpha came out as strongly associated with R–W(INM), while, Spergula arvensis L. and Ammannia baccifera L. emerged as characteristic species in R–C rotation. Thus, it is implied that pulse based cropping and INM could enhance weed seed density with higher species diversity compared with the R–W rotation and RDF in long-run.
Published Version
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