What's the difference between dry seeded rice (DSR) and aerobic rice?

DSR

DSR means different things to different people. In thinking about the answer to the question, we need to be conscious of three totally different crop management aspects:

• the method of planting or crop establishment (transplanting, dry seeding or wet seeding),
• land preparation or tillage (zero tillage, dry/moist tillage, puddling), and
• water management (which can range from continuous flooding to alternate wetting and drying to rainfed)

Strictly speaking, dry seeding is a planting method, nothing more. How water is managed is a totally separate matter.

Before dry seeding, the soil may have undergone dry land preparation. This is done either through conventional tillage (CT-DSR), or through zero till dry seeded rice (ZT-DSR).

As the term suggests, in dry seeding, the soil is not puddled or flooded at the time of seeding.

In irrigated areas in India, the term DSR is commonly used to define more than just the planting method. It is often taken to imply that the crop is NOT grown under flooded conditions i.e., the crop receives irregular but frequent irrigation, such as in wheat. Thus, for a number of people, the term DSR is about both the planting method and water management. This causes the confusion. 

In fact, water management for DSR can vary greatly (just as it can for puddled transplanted rice and wet seeded rice), from continuous flooding for most of the growing season to frequent alternate wetting and drying (AWD), to less frequent AWD, to rainfed.

In the irrigated areas of India where DSR is being introduced, the goal is to achieve similar yield to that of puddled transplanted rice, while minimizing the irrigation input to the rice.

Therefore, the dry seeded rice is not continuously flooded, but is irrigated frequently to avoid yield loss. This means keeping soil water content of the root zone (~0−20 cm) between saturation and field capacity much of the time.

Aerobic rice

Aerobic rice is grown under conditions where the root zone is maintained in a non-flooded or aerobic condition for most of the time. This means that the soil's water content in a significant part of the root zone is allowed to dry down to less than field capacity.

This comes with a yield penalty due to water loss stress. To try and reduce the penalty, special cultivars are being developed with greater drought tolerance, but at the same time with the ability to respond to inputs, especially nutrients.

The System of Aerobic Rice involves growing these specially developed cultivars under aerobic conditions. At present, the yield potential of aerobic cultivars (under well-water conditions) is less than the yield potential of high yielding cultivars bred for puddled transplanted systems grown.

Aerobic rice is usually dry seeded into dry or moist tilled soil like in DSR, although it doesn’t have to be. Aerobic conditions can also be introduced into fields after puddling and transplanting.