Conservation agriculture (CA) has a major influence on the relative abundance of weed species, while weed control is perceived as one of the most challenging issues with the initial adoption of CA. In this first-ever study of the soil weed seedbank in long-term CA experimentsin Bangladesh, we assessed the weed response to tillage practice and residue retention under CA in rice-based cropping systems to determine how weed seedbanks changed over time, and to predict changes in weed management practices that are needed to prepare for more widespread adoption of CA on smallholder, rice-based cropping systems.
Conservation agriculture (CA) has a major influence on the relative abundance of weed species, while weed control is perceived as one of the most challenging issues with the initial adoption of CA. Due to a cessation of tillage, the composition and dynamics of weeds in the soil weed seedbank will change, compared to conventional tillage that leads to shifts in the weed communities.
Minimum soil disturbance of the CA system generally favors the emergence of perennial weed species, relative to annual weed species in the seedbank. It is reported to encourage perennial weeds, such as Cyperus rotundus L., Saccharum spontaneum L., and Sorghum halepense (L.) Pers, in the soil weed seedbank of minimally disturbed soil, since tubers and rhizomes present underground in soil are not buried or uprooted.
Also, in no-tillage systems, the annual grass populations usually increase, concurrent with a decrease in the populations of dicotyledonous weeds. On the other hand, the seedbank of annual and perennial grasses, perennial dicot species, wind-disseminated species, and volunteer crop species was reported to increase, and the annual dicot species was reported to decrease in a reduced tillage (RT) system.
For example, the seedling density of Amaranthus spp. was much higher in the no-till soils than the tilled soils. Notwithstanding the above effects of decreased soil disturbance by CA on the weed seedbank, there have been no comparable studies in the intensive, triple-cropping systems, where there is an annual period of soil submergence for wetland rice crops. Despite its widespread global adoption, in Bangladesh, experimentation on CA began in around 2005, to adapt its practices for smallholder farms. However, studies on weed species composition in the soil seedbank, and their changes after several years of CA practice, have rarely been examined.
Tillage practices, crop rotation, and weed control practices may change the weed seed density in the soil, which affects the soil weed seedbank and the efficacy of weed control practices. Changes in the weed seedbank, due to crop production practices, are an important predictor of subsequent weed problems. Information on the effect of strip tillage and crop residue retention in the intensive cropping pattern on the soil weed seedbank might be a useful background for sustainable weed management in CA.
Hence, in this first-ever study of the soil weed seedbank in long-term CA experiments, at two locations in Bangladesh, we assessed the weed response to tillage practice and residue retention under CA in rice-based cropping systems. The aim was to determine how weed seedbanks changed over time, and to predict changes in weed management practices that are needed to prepare for more widespread adoption of CA on smallholder, rice-based cropping systems.
Two on-farm CA experiments were sampled (in Beluapara after 3 years and Digram after 5 years) in Bangladesh for the effects of strip planting (SP) and bed planting (BP) at both the sites, plus no-tillage (NT) in Beluapara, and increased retention of the residue of previous crops (20% vs.50%).
We concluded that the continued strip planting-based conservation agriculture with 50% crop residue retention for 3–5 years reduced the weed seedbank size and diversity of weed species in the seedbank in contrasting rice-based cropping patterns. However, strip planting, bed planting, and no-tillage increased the proportion of perennial weeds in the weed seedbank, relative to the dominance of annual weeds in conventional tillage.
This may necessitate a change, over time, in weed control strategies. To verify this finding, a more extensive on-farm field study on the soil weed seedbanks under longterm conservation agriculture is suggested.
Also, it is necessary to conduct research on the control of perennial weeds in conservation agriculture systems. Further research is also essential, in order to fully understand the complex relationships of weed species, and how they are affected by different tillage and residue mulch retention levels.
Read the study:
Hossain MM, Begum M, Hashem A, Rahman MM, Haque ME, Bell RW. (2021) Continuous Practice of Conservation Agriculture for 3–5 Years in Intensive Rice-Based Cropping Patterns Reduces Soil Weed Seedbank. Agriculture; 11(9):895.
