Climate-smart agriculture practices influence weed density and diversity in cereal-based agri-food systems of western Indo-Gangetic plains

With conventional management practices, high productivity derived from this continuous RW system are at the cost of over-exploitation of resources (i.e., groundwater, soil, energy) and high use of inputs, (i.e., irrigation, fertilizer, herbicides, and pesticides). The sustainability of the RW system in western Indo-Gangetic plains (IGP) is doubtful due to the rapid decline in soil and water resources, and environmental quality.

Furthermore, continued cultivation of the same cropping system (i.e., rice-wheat system) over the last five decades allowed certain weed species to adapt, increase their establishment, seedbank, and profusion. Such weeds adversely affect resource use efficiency (light, water, and nutrients), and crop productivity. In the western IGP, weed infestation negatively influences wheat production, in particular under conventional wheat management systems. Weeds infestation could decrease wheat yield by 50–80%11 or even 100% in South Asian IGP.

Under the RW cropping system, Phalaris minor is the most predominant weed, due to its ability to survive under anaerobic conditions (created during rice cultivation). Furthermore, P. minor is gaining resistance against numerous common herbicides. Besides its adverse impacts on the environment and its high cost, presently herbicide resistance is emerging at a large scale in different crops and cropping systems making chemical control less reliable. Therefore, weed management is becoming increasingly important in future cropping systems.

Although weeds are a threat to crops, it is an integral component in the agri-ecosystem and could be considered as a bio-indicator for adopted management practices in a particular region. Since applying CA-based management practices within the agro-ecosystem might shift weed density and diversity, thus, only weed species that can adapt to certain crop and management practices will grow and proliferate, while others will disappear. In this way, the emerged weeds might be considered as bio-indicators for applied management practices.

However, due to the negative impression and its impacts on crop production, weeds as bio-indicators in particular agro-ecosystem/region were poorly understood and have found little interest. Climate-smart agriculture (CSA)-based management practices are evolving as a viable and sustainable alternative to conventional RW cropping systems across south Asia for better resources conservation and yield stability.

CSA depends on agronomic aspects for improving systems adaptive capacity, sustaining food security while reducing the environmental footprints, and can influence weed density and diversity composition in particular agro-ecosystems. CSA-based management practices rely on a wide range of indicators, i.e., tillage, crop establishment, crop residue retention, crop diversification, and precise water and nutrient management, along with the use of information and communication tools (ICTs) for timely implementation of crop practices.

Keeping the soil mulch around the year (crop residue retention) and layered with precise water application through subsurface drip irrigation (SDI) helped in more predation and less germination of weeds seeds due to less sunlight and moisture near the soil surface. Besides the well-known benefits of the SDI system (i.e., minimizing evaporation from the soil, efficient water, and fertilizers application and use and reducing labor cost) the SDI system also discourages weed germination and growth. However, most of the research done was conducted with one or two treatment bases like tillage and mulch on the weed community composition, particularly in the wheat-based system.

Research investigations on the assessment of weed community responses to CSA are inadequately understood, which is vital for integrated weed management in the wheat-based cropping systems. Long-term field trials based on CSA practices are required to understand the changes in plant community diversity and composition and could give insight into long-term effects and best ecological indicators “weed species” for different management practices.

We hypothesized that CSA management scenarios (layering of different indicators/practices) could reduce weed density and composition, and diversity indices with no negative impact on wheat performance under rice/maize-based systems

Crop management activities like tillage, crop residue, crop rotations, water application, and nutrients management affect weed diversity and composition. Weed community responses to long-term CSA management practices in cereal-based agri-food systems of western IGP were investigated. The most abundant species were favored by farmers’ practice. However, CSA-based management practices markedly reduced total weeds density and biomass and shifted weed flora towards broadleaf weed species.

The effect of CSA-based management practices on weed flora composition and infestation levels was additive and more evident in the long term. Implementing long-term CSA practices might lead to weed seedbank depletion due to encouraging weed predation factors. Our results indicate that layering of CSA management practices was found to be synergistic means of weed control.

In conclusion, a full CSA-based maize–wheat–mungbean system could be a promising alternative for the RW system for better weed management in western IGP. Besides the measurement of weed density and biomass, in long-term experiments, future studies should also focus on changes of seedbank across years to get more in-depth clarity on weed behavior and dynamics.