Weed Ecology and Weed Management Strategies for Dry-Seeded Rice in Asia

Rice is a principal source of food for more than half of the world population, and more than 90% of rice worldwide is grown and consumed in Asia. A change in establishment method from manual transplanting of rice seedlings to dry-seeded rice (DSR) has occurred in some countries as growers respond to increased costs or decreased availability of labor or water. However, weeds are a major constraint to DSR production because of the absence of the size differential between the crop and the weeds and the suppressive effect of standing water on weed growth at crop establishment. Herbicides are used to control weeds in DSR, but because of concerns about the evolution of herbicide resistance and a scarcity of new and effective herbicides, there is a need to integrate other weed management strategies with herbicide use. In addition, because of the variability in the growth habit of weeds, any single method of weed control cannot provide effective and season-long control in DSR. Various weed management approaches need to be integrated to achieve effective, sustainable, and long-term weed control in DSR. These approaches may include tillage systems; the use of crop residue; the use of weed-competitive cultivars with high-yield potential; appropriate water depth and duration; appropriate agronomic practices, such as row spacing and seeding rates; manual or mechanical weeding; and appropriate herbicide timing, rotation, and combination. This article aims to provide a logical perspective of what can be done to improve weed management strategies in DSR.

Developing direct-seeding options for rice farmers in the Indo-Gangetic Plains

The rice-wheat farming systems of the Indo-Gangetic Plains (IGP) are essential to India’s food security. These systems face multiple threats, however, to the future of the natural resource base. These threats include increased costs for irrigation and fuel, seasonal labor shortages, and unsustainable use of groundwater. In addition, climate change means increasingly variable monsoons that are likely to pose further constraints. Direct-seeded rice, as an alternative to transplanted rice, provides a potential entry point to save labor, reduce reliance on irrigation water, and increase productivity of the wheat crop. Technology options for direct seeding and related weed management were developed and validated in India commencing with on-station experiments and small-scale on-farm trials in 2000 and increasing to a total of more than 100 farmers’ field trials by 2005. These farmers’ trials, which compared both wet and dry direct-seeded rice with transplanted rice, were conducted in the states of Uttarakhand, Uttar Pradesh, and Bihar by four agricultural universities. The trials involved a wide community of farming stakeholders in diverse agroecosystems, and spanned mechanized farms (>2 ha) in Uttarakhand to smallholder farms (>=0.5 ha) in Bihar reliant on manual labor. Direct seeding is ‘knowledge-intensive’ and farmers require access to considerable amounts of information in order to respond to the variability of the monsoon, soil conditions, and weed infestations. Making such information available within the farm communities, and providing them w
ith tools to aid better decision making and the means to evaluate their crop own management, is critical to the successful adoption of such practices. Activities with farmers’ groups have continued since 2005 to validate direct-seeding practices on-farm, and also to explore the constraints to adoption and the information requirements to support effective farmer decision making.

Weed population dynamics, herbicide efficacies, and crop performance in a sprinkler-irrigated maize-rice cropping system

In the future, maintaining food security will require an increase in rice productivity with less land, labor, and water. Agronomic approaches to reducing the water and labor demands of rice-based cropping systems include crop diversification to include crops with higher water productivity, direct-seeded rice, and irrigation scheduling based on soil water potential or alternate wetting and drying cycles. However, weeds are a major constraint to increasing rice productivity in these systems. A two-year study was conducted to identify the changes in weed population and to evaluate the efficacy of herbicides and their effect on crop performance in a sprinkler-irrigated maize-rice cropping system. The dominance of weed species shifted from a grass weed Echinochloa colona to broadleaved weeds, such as Hedyotis corymbosa, Lindernia spp., and Murdannia nudiflora. At 41 days after sowing (DAS) and at tasseling stage, glyphosate application provided a 90-100% decrease in total weed biomass of maize. The combined effects of all the herbicides applied in rice provided almost 100% control in total weed biomass at 40 DAS. However, the herbicide schedule in the cropping system was ineffective in controlling M. nudiflora. The weed control treatments had no significant effect on the yield of maize [8.7 and 11.5 (herbicide-treated) and 8.4 and 12.0 (partially weedy) Mg/ha in 2012 and 2013, respectively], but rice grain yield was influenced significantly. Rice grain yield in herbicide-treated plots in 2012 and 2013 were more than 1.5 and 8.5 times greater than yield achieved in the weedy plots, respectively. A significant negative relationship was found between rice grain yield and weed biomass in both years. Future research in maize-rice cropping systems should focus on the integration of appropriate agronomic practices with herbicide rotation to ensure that weed management strategies are sustainable and effective, and to avoid the risk of herbicide resistance developing in weed populations.

Rice in cropping systems – Modelling transitions between flooded and non-flooded soil environments

Water shortages in many rice-growing regions, combined with growing global imperatives to increase food production, are driving research into increased water use efficiency and modified agricultural practices in rice-based cropping systems. Well-tested cropping systems models that capture interactions between soil water and nutrient dynamics, crop growth, climate and management can assist in the evaluation of new agricultural practices. The APSIM model was designed to simulate diverse crop sequences, residue/tillage practices and specification of field management options. It was previously unable to simulate processes associated with the long-term flooded or saturated soil conditions encountered in rice-based systems, due to its heritage in dryland cropping applications. To address this shortcoming, the rice crop components of the ORYZA2000 rice model were incorporated and modifications were made to the APSIM soil water and nutrient modules to include descriptions of soil carbon and nitrogen dynamics under anaerobic conditions. We established a process fo
r simulating the two-way transition between anaerobic and aerobic soil conditions occurring in crop sequences of flooded rice and other nonflooded crops, pastures and fallows. These transitions are dynamically simulated and driven by modeled hydraulic variables (soil water and floodwater depth). Descriptions of floodwater biological and chemical processes were also added. Our assumptions included a simplified approach to modelling O2 transport processes in saturated soils. The improved APSIM model was tested against diverse, replicated experimental datasets for rice-based cropping systems, representing a spectrum of geographical locations (Australia, Indonesia and Philippines), soil types, management practices, crop species, varieties and sequences. The model performed equally well in simulating rice grain yield during multi-season crop sequences as the original validation testing reported for the stand-alone ORYZA2000 model simulating single crops. This suggests robustness in APSIM’s simulation of the rice-growing environment and provides evidence on the usefulness of our modifications and practicality of our assumptions. Aspects of particular strength were identified (crop rotations; response to applied fertilizers; the performance of bare fallows), together with areas for further development work (simulation of retained crop stubble during fallows, greenhouse gas emissions). APSIM is now suitable to investigate production responses of potential agronomic and management changes in rice-based cropping systems, particularly in response to future imperatives linked to resource availability, climate change, and food security. Further testing is required to evaluate the impact of our simplified assumptions on the model’s simulation of greenhouse gas emissions in rice-based cropping systems.

A Decade of Plant Proteomics and Mass Spectrometry: Translation of Technical Advancements to Food Security and Safety Issues

Tremendous progress in plant proteomics driven by mass spectrometry (MS) techniques has been made since 2000 when few proteomics reports were published and plant proteomics was in its infancy. These achievements include the refinement of existing techniques and the search for new techniques to address food security, safety, and health issues. It is projected that in 2050, the world’s population will reach 9-12 billion people demanding a food production increase of 3-70% (FAOQ3, 2009. How to feed the world in 2050, high-level expert forum. Rome: Food and Agriculture Organization of the United Nations) from today’s food production. Provision of food in a sustainable and environmentally committed manner for such a demand without threatening natural resources, requires that agricultural production increases significantly and that postharvest handling and food manufacturing systems become more efficient requiring lower energy expenditure, a decrease in postharvest losses, less waste generation and food with longer shelf life. There is also a need to look for alternative protein sources to animal based (i.e., plant based) to be able to fulfill the increase in protein demands by 2050. Thus, plant biology has a critical role to play as a science capable of addressing such challenges. In this review, we discuss proteomics especially MS, as a platform, being utilized in plant biology research for the past 10 years having the potential to expedite the process of understanding plant biology for human benefits. The increasing application of proteomics technologies in food security, analysis, and safety is emphasized in this review. But, we are aware that as no unique approach/technology is capable to address the global food issues. Proteomics-generated information/resources must be integrated and correlated with other omics-based approaches, information, and conventional programs to ensure sufficient food and resources for human development now and in the future.

Productivity and Sustainability of the RiceeWheat Cropping System in the Indo-Gangetic Plains of the Indian subcontinent: Problems, Opportunities, and Strategies

Rice and wheat are the staple foods for almost the entire Asian population and therefore they occupy a premium position among all food commodities. The era of the Green Revolution started during the early 1970s with wheat and rice and since then the ricee-heat cropping system of the Indo-Gangetic Plains has played a significant role in the food security of the region. However, recent years have witnessed a significant slowdown in the yield growth rate of this system and the sustainability of this important cropping system is at risk due to second-generation technology problems and mounting pressure on natural resources. Traditional cultivars and conventional agronomic practices are no longer able to even maintain the gains in productivity achieved during the past few decades. Demand for food is increasing with the increasing population and purchasing power of consumers. The ricewheat cropping system is labor-, water-, and energy-intensive and it becomes less profitable as these resources become increasingly scarce and the problem is aggravated with deterioration of soil health, the emergence of new weeds, and emerging challenges of climate change. Therefore, a paradigm shift is required for enhancing the system’s productivity and sustainability. Resource-cons
erving technologies involving zero- or minimum-tillage in wheat, dry direct seeding in rice, improved water- and nutrient-use efficiency, innovations in residue management to avoid straw burning, and crop diversification should assist in achieving sustainable productivity and allow farmers to reduce inputs, maximize yields, increase profitability, conserve the natural resource base, and reduce risk due to both environmental and economic factors. A number of technological innovation and diversification options have been suggested to overcome the system’s sustainability problems but some of them have not been fully embraced by the farmers as these are expensive, knowledge-intensive, or do not fit into the system and have resulted in some other unforeseen problems. Different concerns and possible strategies needed to sustain the riceewheat cropping system are discussed in this review on the basis of existing evidence and future challenges.