Wheat is a principal crop staple in South Asia with current cultivation extending across 36.1 million ha; around 73% of this area is in India where wheat provides approximately 21% of the aggregate food energy and 17% of the dietary protein on a national scale. Projections suggest that wheat production in India alone will need to increase by 30% from current levels of around 110 million tons to 140 million tons by 2050 to keep pace with domestic requirements.
Because reserves of potentially cultivatable land are extremely low in South Asia, future production increases must emerge from yield intensification rather than cultivated area expansion. Hence, identifying the magnitude and causes of wheat yield gaps (that is, the difference between potential and achieved crop productivity) is essential for prioritizing and effectively targeting policies and programmes for sustainable agricultural development.
A study on ‘Time management governs climate resilience and productivity in the coupled rice–wheat cropping systems of eastern India’ by Andrew J McDonald et al looks at the issue in detail. Through a dense network of on-farm surveys for the rice–wheat system in this region, the study published in the journal Nature shows that contemporary wheat sowing dates have a central influence on achieved and attainable yields, superseding all other crop management, soil and varietal factors.
South Asia’s principal wheat growing area is the Indo–Gangetic Plain, where dry-season wheat is commonly grown in rotation with wet-season rice (that is, the rice–wheat system). The rice-wheat system occupies about 10 million ha in India. The western Indo–Gangetic Plain includes the Indian states of Punjab and Haryana and has the highest mean levels of wheat productivity in the region (4.5 t/ha).
However, modest yield gaps (9–12%) together with accelerating production challenges such as groundwater depletion have drawn into question the long-term sustainability and potential for yield intensification in these states. As a consequence, Indian policymakers have prioritized staple crop intensification in the Eastern Ganges Plain region, including Bihar state and the eastern districts of Uttar Pradesh state through initiatives such as ‘Bringing the Green Revolution to eastern India’ to meet current and future food security challenges.
Wheat yield gaps in the EGP are among the highest in India and have been variously attributed to a range of factors, including late sowing, use of older cultivars, complex weed flora, variable access and low utilization of irrigation water and labour shortages. Late wheat sowing creates substantial climate hazards from heat stress by delaying crop reproductive growth into the spring period (that is, March through early April) when temperatures warm considerably.
Heat stress reduces photosynthetic efficiency and can shorten the grain-filling duration through premature crop senescence, thereby reducing biomass production, harvest index and crop yield. Although several studies have confirmed the importance of timely sowing for avoiding yield losses from heat stress, the contribution of current sowing date patterns to yield gaps is insufficiently characterized in South Asia.
Moreover, few contemporary studies assess the enabling factors that determine the capacity of farmers to make sowing date adjustments. It is also important to note that the rice-wheat systems of South Asia are not simply a set of crops grown in sequence but rather reflect an interlinked set of management decisions that often involve yield or sustainability trade-offs.
Consideration of yield gaps is no exception and must be conceptualized at the cropping system level rather than for wheat alone. In the context of this study, it uses the concept of ‘climate resilience’ to refer to the capacity of planting date adjustments to enhance crop yields, yield potential and yield stability by reducing exposure to less favourable growing conditions.
By combining field and household survey data, time series remotely sensed information and dynamic crop simulation, this study of rice-wheat systems in the Eastern Ganges Plains of India has four interlinked objectives:
- quantification of the importance of planting dates to current wheat yields, yield potential (Yp) and yield gaps (YG),
- ex ante opportunity assessment of gains in wheat yield potential achievable through planting date adjustments,
- identification of enabling and constraining factors that contribute to the timing of wheat planting and
- simulation-based assessment of rice-wheat system-level strategies for enhancing climate resilience through planting date adjustments.
Together, these objectives seek to establish the importance of cropping calendar management (‘keeping time’) to the performance of RW systems in the stress-prone EGP to inform sustainable intensification and climate adaptation strategies in the region.
Discussion
The study estimates that untapped wheat production potential will increase by 69% with achievable adjustments to wheat sowing dates without incurring undesirable trade-offs with rice productivity, irrigation requirements or profitability.
The results of the analysis suggests that major gains in wheat productivity are achievable in the Eastern Gangetic Plains if management is modified to ensure timely wheat establishment as a mechanism for climate resilience. By combining changes in rice and wheat management, greater adjustments to the annual cropping calendar are anticipated to increase wheat yield potential by an average of 0.84 t/ha, thereby providing greater scope for yield increase, food security and income generation in the Eastern Ganges Plains. This represents a 69% increase in the attainable wheat yield gap over a baseline estimate of 0.78 t/ha.
If these gains are realized, they would transition our study region from being a net wheat importer to an important source of wheat for other food-insecure regions in South Asia. This outcome aligns with the agricultural development policy ambitions established by the government of India through the National Food Security Mission and special initiatives therein, including Bringing the Green Revolution to eastern India.
Transitions to timely wheat planting will probably increase system reliability by reducing interannual production variability and, crucially, there are no anticipated trade-offs with rice wheat systems-level productivity if rice is managed in a manner to ensure timely wheat establishment. As the favourable thermal window for dry-season wheat shrinks in South Asia with progressive climate change, timely wheat establishment will probably assume even greater importance for yield and production reliability in the Eastern Ganges Plains.
Nevertheless, the challenge of scaling innovative management strategies to optimize the annual cropping calendar is not typically a simple task because many farmers must take several steps beyond simply choosing to plant earlier to implement a new time management strategy.
This is particularly true in the case of the coupled rice-wheat systems of the Eastern Ganges Plains where rice harvest date exerts strong control over the timing of wheat planting. Further, there is a notable spatial dimension to the early-planting opportunity, with the northern half of our study area constituting the priority area for action.
There are several potential pathways towards effective time management of the RW cropping calendar that differ with respect to investment costs and other factors affecting feasibility and desirability of adoption. Here it briefly describes six of the more promising options that can be implemented independently or, in some cases, as complementary strategies that may collectively return gains in crop productivity and resilience beyond those estimated in this study through more radical adjustments to the cropping calendar.
Each of these adaptation pathways has its own risks, investment requirements and scaling considerations. Broadly speaking, technology adoption constraints can be related to insufficient awareness of an innovation, limited or unaffordable access, a heterogeneous range of expected benefits or institutional and policy hurdles. For most of farmers in the area, the use of mechanization technologies to facilitate timely wheat establishment and other management goals is not only a household-level decision but rather one that is conditioned by access to service providers.
The findings also indicate that transformative gains in wheat yields are only possible in eastern India if rice and wheat are managed as a coupled system. Steps taken to ‘keep time’ through better management of the annual cropping calendar will pay dividends for food security, profitability and climate resilience now and as a foundation for adaptation to progressive climate change.
The full paper can be accessed here