Changes in the Weed Seed Bank in Long-Term Establishment Methods Trials under Rice-Wheat Cropping System

Abstract

The rice-wheat cropping system in the Indo-Gangetic Plains is the backbone of food security in India. In the 1990s, due to the scarcity of resources, the traditional Crop Establishment (CE) method shifted from Conventional Till Puddle Transplanted Rice (CTPTR) to CT Direct Seeded Rice (CTDSR) and Zero-Till DSR (ZTDSR) in paddy; and in wheat, from Conventional Till Wheat (CTW) to Zero Till Wheat (ZTW), with residue retention in rice (RRR) or in both rice and wheat (RRRW). Shift in CE methods led to change in Weed Seed Bank (WSB) dynamics and ultimately affected the weed management program. After five years of field trials, soil samples were drawn as per 2-factors factorial randomized block design. Factor-I comprised 4-CE methods, whereas factor-II consisted of 3-soil depths (0-10, 10-20 and 20-30 cm). Results showed CTPTR-CTW and ZTDSR-ZTW (RRRW) record the highest seed bank (SB) of grasses, sedges and BLWs as total weeds, in general; and predominant weeds like Echinochloa spp., Ammania baccifera, Commelina benghalensis and Digitaria sanguinalis, in particular. It also showed the higher species richness (D Mg ) and Shannon-Weaver (H') indices. CTDSR-CTW and CTDSR-ZTW (RRR) show the lowest WSB and at par with Shannon-Weaver (H') index; further, lowest species richness (D Mg ) under CTDSR-CTW. Species Evenness (J') and Simpson index (λ) vary non-significantly with CE methods. Furthermore, 0-10 cm soil depth showed the highest SB of different category of total weed, predominant weeds as well as higher values of D Mg , H', and λ; whereas reverse trend was observed in Whittaker Statistic (β W ). Interaction between CE methods and soil depth revealed most of WSB lying on the top layer in case of ZTDSR-ZTW (RRRW) and CTDSR-ZTW (RRR); while CTPTR-CTW showed almost uniform WSB distribution, and in case of CTDSR-CTW, a gradual decrease in WSB with soil depth.

Crop Establishment with Conservation Tillage on Viable Weed Seed Density and Diversity in Soil, Crop and Water Productivity under RWCS in North-West IGP: A Review

“…Emergence of P. minor, Chenopodium album, and R. dentatus was inhibited by 45, 83 and 88%, respectively at 6 t/ha rice residue load com-pared to without residue mulch (Kumar et al, 2013). Sharma et al(2020) also found that CTDSR-CTW recorded the lowest Shannon-Weaver (H) and Species richness (D Mg ) while the highest in CTPTR-CTW, statistically at par with CTDSR-ZTW (RRR) and ZTDSR-ZTW (RRRW). Conversely, the highest β W was observed under the CTDSR-CTW and the lowest in CTPTR-CTW which is at par with CTDSR-ZTW (RRR) and ZTDSR-ZTW (RRRW).…”

“…Density of broad-leaf weeds particularly C. album was more in CT-ZT treatment followed by ZT-ZT and MT-ZT treatments at both soil depths. Sharma et al, (2020) reported that the vertical distribution of SB of grasses, sedges, BLW, and total weeds had been affected by the different CE methods (Fig. 4a).…”

Soil weed seedbank under different cropping systems of middle Indo-Gangetic Plains

“…However, weed species not available in the "Composite List of Weeds" were verified by Xu and Deng (2017) and Walia (2016). From the data of emerged weed, the weed community structure was analysed using the WDI like, Shannon-Weaver (H'), species richness (D Mg ), species evenness (J'), Simpson index (λ) and Whittaker statistics (β W ) as per the methodology used by Sharma et al (2020).…”

“…Furthermore, currently, most of the weed dynamics studies in different cropping system either quantifies the weed population dynamics by counting the above-ground germinated weeds (Shivran et al 2017, Kumar et al 2018 or WSB in response to different agronomic practices, like tillage, crop rotation, fertilisation or weed management (Lal et al 2016, Sharma et al 2020. A weed dynamics study based on the above-ground germinated weeds did not give the real picture of potential weed problems due to WSB in future.…”

Tillage and crop establishment effects on weeds and productivity of a rice-wheat-mungbean rotation

“…Soil disturbance, crop rotations and crop management practices have a strong influence on weed seedbank and species densities ( Grundy et al, 2003 , Koocheki et al, 2009 , Hosseini et al, 2014 , Chen et al, 2017 , Weisberger et al, 2019 ). A change in tillage and crop establishment methods influences species composition by direct killing of weeds or by redistributing weed seeds in different soil depths, and by changing the soil environment and thereby affecting the weed seed germination and emergence ( Samarajeewa et al, 2005 , Nichols et al, 2015 , Sharma et al, 2020 ). Tillage can stimulate some weed seeds to germinate and bury other seeds which can remain viable in the soil for many years.…”