Dry direct-seeded rice (DDSR) offers several advantages: rapid planting, easy mechanization, less labor and water requirement, and early maturity with fewer environmental footprints. Despite these recompenses, the major snag with practicing DDSR is the potential biotic threat posed by weeds. The yield losses under DDSR are estimated as high as 75%. Thus, weed management shares a very high relative importance, ranking among different agronomic management options for higher productivity in DDSR.
Several constraints involved with transplanted puddled rice (TPR), namely a huge water demand for puddling and maintaining continuous flooding; a huge energy requirement, and almost 15–20% higher labor inputs over direct-seeded rice (DSR), have made it unaffordable for many farmers, especially for small and marginal farmers in Southeast Asia.
Furthermore, repeated plowing for puddling breaks capillary pores, disperses clay particles, and destroys aggregate stability in the topsoil, resulting in a hardpan creation at the shallow depth. Dry direct-seeded rice (DDSR) is an impending version of upland rice cultivation practiced widely to save water, labor, and energy over TPR. The rice crop is established by sowing the seeds directly in the non-puddled and non-saturated soil. DDSR can be adopted both as upland rice and aerobic rice.
The advantages offered by DDSR, namely rapid planting, easy mechanization, less labor and water requirement, and early maturity with fewer environmental footprints have brought almost 22% of the total rice area in Asia under DSR. In fact, DDSR is one of the oldest methods of rice establishment and before the 1950s it was very popular but was gradually replaced by TPR. The traditional rain-fed systems of rice cultivation instinctively fall under DSR.
However, the non-conventional areas of rice cultivation like the trans-Indo Gangetic Plains of India have also reported yield enhancement and water-saving under DDSR followed by yield increment in the subsequent wheat crop also under the rice-wheat system.
Variable yield response and water productivity in DDSR have been reported by numerous researchers worldwide depending on location and the type of agronomic management adopted. The rice productivity of over 7 tons/hectare (t/ha) under DDSR with good agronomic management was reported by the International Rice Research Institute back in the early 1970s in the Philippines and Peru and then from 8.4 to even 10.3 t/ha across the world.
Despite these recompenses, the major snag with practicing DDSR is the potential biotic threat posed by weeds. The yield losses under DDSR are estimated as high as 75%, which exhausts more than 30% of the total cost incurred in rice cultivation. The concurrent crop and weed growth and the absence of standing water in the initial crop establishment phase aggravate weed insurgence in DDSR. Under these systems, weeds could be managed by hand weeding (manual means), through herbicides, or by a combination of both.
However, chemical weed management is replacing manual weeding due to meager labor availability, escalating labor costs, and drudgery involved. The newer low dose high-efficacy herbicides are convenient and have made DDSR viable, especially with high-yielding short-duration varieties. However, there have been grave apprehension about the solitary use of herbicides in the recent past due to the development of resistance in weeds, changes in the weed density and composition, and the emerging negative environmental footprints.
Amidst these concerns, the adoption of any single approach remains both insufficient and ineffective for sustainable weed management in DDSR and the present review emphasizes integrated weed management practices for DDSR. We have also attempted to identify opportunities for the plausible integration of region-specific weed management in an economic and effective way to reap the benefits offered by DSR.
DDSR could be practiced in rain-fed upland, lowland, and also flood-prone areas. Globally, out of the total 161 million hectares under paddy cultivation, DSR is being practiced on about 33 million hectares. The aerobic soil environment in DDSR saves water, but with the absence of stagnating water and the lack of a “head start” in rice seedlings over germinating weed seedlings; the weed menace in DSR is aggravated.
The critical period of weed competition in DDSR remains up to 41 days after sowing (DAS), yet a weed-free situation until 70 DAS remains desirable for higher productivity. Weeds, when not controlled during this period, may reduce yields from 15 to 100%. The intense competition for water, nutrients and solar radiation posed by weeds reduces yield and grain quality. Poor weed control is the second major yield barrier after an inadequate water supply in DDSR worldwide, the range of maximum and minimum yield losses, however, differ under varying ecologies.
The yield losses remain higher under DDSR over TPR. An approximate 35% yield loss has been reported in TPR, however, under DDSR it may reach as high as 100%. Out of the total 40% yield loss in rice caused by various pests, weeds create nearly 10% of the yield loss, which under DSR may go up to 32%.
Thus, weed management shares a very high relative importance, ranking among different agronomic management options for higher productivity in DDSR.
DDSR with appropriate agronomic interventions can produce similar yields as that of TPR and remains a feasible substitute for TPR under a labor and water shortage. A systematic weed-monitoring program for implementing successful integrated weed management is required, wherein different weed-management approaches namely cultural weed management through stale seedbed and crop residue mulch, utilizing crop-competitiveness by growing suitable cultivars and altering seed rate, row spacing, nutrient and water management can enhance the crop competitive ability.
Needs-based chemical weed management through herbicide, herbicide mixture, identification of new herbicides against a wide spectrum of weeds, and use of HT rice, would help in achieving a long-term and sustainable weed control in DDSR. The newer technologies for assessing weed losses through crop models and exploring self-suppressive allelopathy remain desirable.
These agronomic and technological innovations have made weed management very effective and economical by reducing the weed-management costs incurred in curative tactics in DDSR. Also, developing new rice cultivars suitable for direct dry sowing and short-statured ideotypes with higher initial vigor would help the wider adoption of DDSR.
Read the study:
Shekhawat K, Rathore SS, Chauhan BS. (2020) Weed Management in Dry Direct-Seeded Rice: A Review on Challenges and Opportunities for Sustainable Rice Production. Agronomy 10(9):1264.