by Noriko Kanno, Ricardo Garcia, Roel R. Suralta, Aurora M. Corales, Crisanta S. Bueno, Niño P.M.C Banayo, Pompe C. Sta. Cruz, Virender Kumar, and Yoichiro Kato
In Asia, rapid economic growth has also caused a shift of labor from agriculture to other industries, and the increase in farm labor demand has increased the labor cost for rice cultivation. To address these water and labor shortages, dry direct seeding of rice (DDSR) is increasingly being used across Asia. The objective of this study was to examine the effects of different sowing depths on crop growth, phenology, and grain yield of DDSR.
Conventional rice (Oryza sativa L.) farming with transplanting in puddled fields requires large amounts of water and labor. The total seasonal water input to rice fields is typically 1300 to 1500 mm, which is two to three times the amount required by other cereals.
However, water for rice cultivation is becoming increasingly scarce owing to the lowering of groundwater levels and declining river flows in many parts of Asia. Climate change is also leading to more extreme precipitation patterns, leading to an uncertain water supply.
In Asia, rapid economic growth has also caused a shift of labor from agriculture to other industries, and the increase in farm labor demand has increased the labor cost for rice cultivation.
To address these water and labor shortages, dry direct seeding of rice (DDSR) is increasingly being used across Asia. In the conventional transplanting method, young seedlings are transplanted into puddled and submerged soil.
In DDSR, dry seeds are sown directly into dry soils. DDSR can save up to 40% of seasonal water input and 60% of the labor input compared with conventional transplanting. Grain yield in DDSR is generally 15% lower than that in conventional transplanting, but it is possible to achieve similar yield with appropriate crop management starting with good seedling establishment, followed by prevention of weed infestation.
However, dry spells during germination often cause poor crop establishment in DDSR. Drought can decrease the percentage emergence (%emergence) to between 30% and 60%, leading to a low tiller number and low ground coverage.
The poor crop establishment also leads to severe competition with weeds. To avoid the risk of low plant density, farmers tend to increase their seeding rates, resulting in increased seed costs. Despite the recommended rate of 20 to 60 kg/ha, actual seeding rates range from 100 to 400 kg/ha in the tropics.
A potential solution to mitigate drought effects on seedling establishment is deep sowing. Common practice for DDSR is to broadcast seeds on the soil surface or to drill seed to a depth of 1 to 2 cm. By placing seeds deeper in the soil, the residual moisture below the surface can be utilized and seed predation by birds can be minimized. This technique has been tested in maize and wheat. These dryland species have greater emergence with a sowing depth of 6 to 10 cm than with conventional shallow sowing (2 to 3 cm) under drought.
In DDSR, on the other hand, this technique has rarely been used. The %emergence of rice sharply decreases with increasing sowing depth, but these studies investigated only seedling establishment. The effect of deep sowing on crop growth, phenological development, and grain yield has not been reported. It is likely that deep sowing will affect the subsequent growth after emergence, since germinated plants must consume stored carbohydrates in seeds during shoot elongation in the soil.
Cultivars of rice, as well as maize and wheat, differ in their ability to emerge from deeper in the soil In DDSR, some cultivars completely fail to emerge when sown at a depth of 5 cm, whereas others can maintain high %emergence at a depth of 7 cm.
However, it remains unclear whether cultivar difference in the %emergence under deep sowing would affect grain yield. The morphological characteristics that contribute to seedling emergence under deep sowing should also be identified to support effective use of this technique. This is particularly important given that poor seedling establishment is one of the major yield constraints in DDSR areas across Asia.
Deep sowing, which is proven to be an effective solution to this problem in wheat and maize cropping, must be tested in rice to confirm its applicability. The objective of this study was to examine the effects of different sowing depths on crop growth, phenology, and grain yield of DDSR.
This is the first report to evaluate rice productivity under deep sowing in both the tropics and the temperate region. Deep sowing (6 to 7 cm) reduced the %emergence, which resulted in lower tiller and panicle density, which in turn led to lower yield than with shallow sowing; however, the heading date was not significantly affected.
The results suggest that differences among cultivars in yield stability under deep sowing can be attributed to a cultivar’s deep-sowing tolerance (i.e. its ability to achieve satisfactory seedling emergence under deep sowing).
The morphological traits of the seedlings, such as the lengths of the mesocotyl and of the first and second internodes, will contribute to deep-sowing tolerance. The knowledge of seedling establishment and subsequent growth of deep-sown rice provided by this study will be useful in developing appropriate sowing techniques and in identifying or developing cultivars that are tolerant of deep sowing for use in DDSR.
Read the study:
K Noriko, Garcia R, Suralta R, Corales A., Bueno C, Banayo N, Sta. Cruz P, Kumar V, and Kato Y (2023) Deep sowing of dry direct-seeded rice: cultivar differences in seedling establishment and grain yield. Plant Production Science.
