**2. Importance of tillage options on weed infestation in the crop field**

Weed management strategies are the key to success of the conservation agriculture based crop production especially at the beginning of 2 years. With the shift from conventional agriculture to conservation agriculture there will be a shift dynamic change in weed species, population and diversity. Therefore, initial weed management is an important phenomenon through integrated weed management approaches like stale seed-bed, mulch, and adjustment in planting dates, biological and mechanical control and effective combination use of herbicides. The many

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*Chemical Weed Management in Maize (*Zea mays *L.) under Conservation Agricultural Systems…*

long-term studies clearly indicated that if the proper weed management options adopted at initial 2 years then the weed population significantly reduced with time under CA-based practices than conventional practices [17–19]. Tillage systems affect the composition of weeds in a field [20]. Typically, perennial weeds in conventional tillage systems cannot be fixed due to repeated plowing but alteration of soil between the surface to sub-surface exposes new weed seeds. In the other hand, the perennial weeds are more prominent initially in CA-based tillage but also broadleaf weeds may be prominent due to the light-weight and density of seeds which remain on the surface facilitate for conducive germination environment. The several studies showed that *Phalaris minor* populations significantly reduced under zero tillage but broadleaves especially *Rumex* found increases [21–23]. A recent study in the EGP suggested, if initial weeds are not managed properly then *Polygonum* species and sedges dominated under CA systems. However, perennial weeds in these systems, the plant roots are not pulled out shall be subject to the complete eradication [24] may regenerate again. [25] reported that dry weight of weeds in crops without plowing method compared to conventional tillage crops decreased by respectively 61 and 77%. Another earlier findings [26] observed that nutrients uptake by crops under CA systems was enriched when weeds was in CA-system were reduced. CA-based agricultural systems conserve the soil health through improving the soil organic matter as well as soil microbial finally leading

*DOI: http://dx.doi.org/10.5772/intechopen.89030*

for the higher productivity of crops [27, 28].

**3. Major weed species in association with maize**

*conyzoides, Medicago denticulate, Avena ludoviciana* etc. [32, 33].

A field experiment found that the most dominant weeds in maize field were sedge *C. rotundus* and dicot weeds *T. portulacastrum*, *D. arvensis*, *P. niruri* and grass *C. dactylon* [34]. In USA, it observed the most common broadleaves weed species

Infesting weed species in crop field generally depend on crop species, cropping systems and their management practices, environmental conditions, seasonal variation, soil properties, nutrients and moisture status as well as soil types. The Eastern Gangetic Plain (EGP) as known for high weed seed bank in soils especially lower EGP (Bangladesh and West Bengal) due to flash and steady floods bring weed seeds from distance in their catchment areas. The weed species also highly depend on seasons as maize is grown round the year in three seasons i.e. Kharif (Monsoon; June– September), Rabi (Winter; November–May) and Kharif 1 (Spring; February–June). The high weed seed pressure and diversity make more difficult to manage weeds manually in conservation agriculture as well as also in conventional agriculture. Grasses weed species during Kharif season in the maize field in EGP are *Echinochloa colona* (L.), *Digitaria ciliaris* (L.), *Leptochloa chinensis* (L.), *Dactyloctenium aegyptium, Cynodon dactylon, Echinochloa crus-galli, Eleusine indica, Setaria viridis, Panicum javanicum, Paspalum commersonii* etc. The broadleaf weeds are *Marsilea minuta, Polygonum hydropiper, Galinsoga ciliata, Physalis heterophylla, Heliotropium indicum, Phyllanthus niruri, Euphorbia hirta, Jussiaea repens, Amaranthus spinosus, Amaranthus viridis, Spilanthes paniculata, Lindernia anagallis, Paspalum distichum* etc. and the major sedges weeds are *Cyperus rotundus, Cyperus difformis, Cyperus iria, Eclipta prostrata, Ludwigia octovalvis, Portulaca oleracea, Fimbristylis miliacea, Scirpus* spp. etc. [29–31]. The perennial weeds species dominant round the years but the seasonal weeds are different when maize grown in dry season (winter maize) and the major dominant weeds are *Polygonum persicaria, Polygonum pensylvanicum, Polygonum orientale, Oldenlandia diffusa, Oldenlandia aquatic, Oxalis corniculate, Chenopodium arvensis, Physalis minima, Solanum nigrum, Hydrocotyle ranunculoides, Ageratum* 

*Chemical Weed Management in Maize (*Zea mays *L.) under Conservation Agricultural Systems… DOI: http://dx.doi.org/10.5772/intechopen.89030*

long-term studies clearly indicated that if the proper weed management options adopted at initial 2 years then the weed population significantly reduced with time under CA-based practices than conventional practices [17–19]. Tillage systems affect the composition of weeds in a field [20]. Typically, perennial weeds in conventional tillage systems cannot be fixed due to repeated plowing but alteration of soil between the surface to sub-surface exposes new weed seeds. In the other hand, the perennial weeds are more prominent initially in CA-based tillage but also broadleaf weeds may be prominent due to the light-weight and density of seeds which remain on the surface facilitate for conducive germination environment. The several studies showed that *Phalaris minor* populations significantly reduced under zero tillage but broadleaves especially *Rumex* found increases [21–23]. A recent study in the EGP suggested, if initial weeds are not managed properly then *Polygonum* species and sedges dominated under CA systems. However, perennial weeds in these systems, the plant roots are not pulled out shall be subject to the complete eradication [24] may regenerate again. [25] reported that dry weight of weeds in crops without plowing method compared to conventional tillage crops decreased by respectively 61 and 77%. Another earlier findings [26] observed that nutrients uptake by crops under CA systems was enriched when weeds was in CA-system were reduced. CA-based agricultural systems conserve the soil health through improving the soil organic matter as well as soil microbial finally leading for the higher productivity of crops [27, 28].
