Long-term impact of zero-till residue management in post-rainy seasons after puddled rice and cropping intensification on weed seedbank, above-ground weed flora and crop productivity

Regulation in weed seed recruitment to soil and its emergence is an ecological approach of weed management for sustainable cropping intensification and land restoration. Intensive tillage operations in rice (Oryza sativa L.) - wheat (Triticum aestivum L.) system is a predominant practice in the South East Asian countries. This practice has emerged as an unsustainable crop management options. Consequently, zero tillage (ZT) in post-rainy seasons after conventional tilled (CT) puddled transplanted rice is being adopted to minimize tillage intensity in system in these regions. However, long-term impact of continuous CT in all seasons versus seasonal ZT (in post-rainy seasons) after puddled transplanted rice with crop residues in cropping system mode on above- and below-ground weed density and diversity is not adequately studied. Hence, we examined four tillage based residue management: (i) conventional tillage in each crop of rotation without residue (CT-CT), (ii) conventional tillage in each crop with incorporated residue (CT-CT + R), (iii) conventional tilled puddled transplanted rice - zero tillage in post-rainy season crops without residue (CT-ZT), (iv) conventional tilled puddled transplanted rice - zero tillage in post-rainy season crops with surface residue mulch (CT-ZT + R) each with three levels of crop rotation: (i) rice - wheat (R-W), (ii) rice - chickpea (Cicer arietinum L.) (R-C), (iii) rice - chickpea - mungbean (Vigna radiata (L.) (R-C-Mb) in split-plot design in Kanpur, India. Zero tillage in post-rainy seasons after conventional tilled rice resulted in 11%, 23%, and 13% lower (P < 0.05) weed seed density than CT-CT at 0-7.5, 7.5-15, and 0-15 cm depth, respectively. However, zero-tilled residue management had 15-19% and 10-14% (P < 0.05) higher above-ground weed density compared with CT-CT. Rice-chickpea-mungbean rotation reduced weed seed density by 6-11%, 4-11%, and 6-8% (P < 0.05) than those of rice-wheat and rice-chickpea across depth. In contrast, rice-chickpea-mungbean had 30-38% higher total above-ground weed density than rest of the crop rotations. Post-rainy seasons zero tillage with and without residues attributed higher weed diversity indices (Shannon and Simpson) compared with conventional tillage in seedbank. Importantly, CT-ZT + R with R-C-Mb (interaction) reduced 24% total viable seed density at 0-15 cm depth than CT-CT with R-W. Further, this system brought about 15% and 62% higher rice seed yield and system productivity over CT-CT with R-W, respectively. Conventional tilled puddled transplanted rice - zero tillage with added residues increased 16% and 33% seed yield of wheat and chickpea compared with CT-CT (P < 0.05), respectively. Thus, it can be concluded that zero tillage in post-rainy seasons after puddled transplanted rice and intensive pulse based cropping (rice-chickpea-mungbean) can minimize viable weed seeds in soil vis-a-vis above-ground weed density over time than conventional tillage and rice-wheat system. The reduced weed density could reduce soil fertility degradation, enhance crop/system productivity, restore soil health and provides opportunity for sustainable cropping intensification in rice ecologies of the Indo-Gangetic plains.

Automated summary

The study examined the impact of different residue management approaches on above- and below-ground weed density and diversity. Results showed that zero tillage with residue management reduced underground weed seed density but increased above-ground weed density.