2 November 2012

4 minute read

In recent years there has been an improvement in management practices for establishment and weed control in drill sown rice.

This has come about through a combination of factors including the development of a ‘direct drill rice recipe’ from Rice Research Australia Pty Ltd (RRAPL) at Jerilderie in recent research into weed management and other technologies.

Site preparation

Early site preparation is a major factor in successfully establishing a drill sown crop. Start preparing the field in autumn, with the aim of having level, evenly sloped bays with no hollows for water to lay.

Rebuilding banks and cleaning out toe furrows to ensure that drainage can occur as quickly as possible is critical for the rice establishment period.

The preferred option for drill sown rice is to prepare the field early and then control weeds using herbicides over winter, leaving a firm seed bed to direct drill the rice into in the spring.

Bankless channels and large outlets aid filling and draining of the bays. This also improves irrigation efficiency and offers the added bonus of automation in some cases. A good recycling system enables the capture of drainage water, but can also supplement supply to reduce the watering time.

Sowing time

Sowing time is a compromise between choosing the best time for seed germination and seedling establishment (warmer temperatures) and ensuring that microspore occurs when the warmest night temperatures occur (between 20th January and 10th February).

Drill sown rice takes one week longer, on average, to maturity than aerial sown crops, so it should be sown and flushed at the beginning of the sowing window for each variety. Emergence will take 7–10 days depending on soil type, sowing depth and soil temperature.

Management at sowing

Seed placement

Ideally seed should be placed at a depth of 30 mm (loam soils) and 50 mm (crusting soils) or below the depth of the crust. If sown too shallow the soil around the seed dries out too quickly and will need additional follow up irrigations to keep the seed moist enough for successful establishment to occur. These additional irrigations mean the soil will remain too moist for ground rig operations, limiting the timeliness of the first weed control.

When checking seed depth, consider how much soil will spill into the seed furrow on first watering (Figure 1). This is less of an issue with disc seeding. The seeding depth will often be deeper than first imagined. Smooth an area of 0.5 m by 0.5 m so that it is level. Carefully scratch soil away until the seeds are exposed without disturbance then measure from the seed to soil surface to determine seeding depth.

Figure 1: It is important to consider movement of the soil from the inter-row to the seeding row with the first watering in the determination of seeding depth.

Sowing too deep (i.e. greater than 50 mm) will make it difficult for the seedling to push through the soil and emerge. Disc seeders often give superior seed placement and depth control compared to tyned seeders in dry seeding situations.

Sowing rate

Sow the rice seed at between 130 kg/ha and 150 kg/ha. Lower seed rates should produce similar yields in good years. However, difficult conditions during establishment can have a bigger impact on lower plant populations from lower seeding rates than those recommended above.

Row spacing

Research into row spacing in rice, conducted by Smith and Ford (2012), has shown no grain yield penalty when row spacing is increased from 18 cm (7?) to 30 cm (12?) for the varieties Amaroo and Reiziq. However the wide row spacing of 30 cm restricted canopy closure (Figure 2), which can allow late germinations of grass and aquatic weeds to occur.

Figure 2: Rice sown on 30 cm row spacing showing incomplete canopy closure allowing light penetration to the soil surface which can allow continued and late germinations of weeds.

Fertiliser at sowing

Only apply fertiliser with the seed at sowing if soil phosphorus (P) levels are low. If soil Colwell P is less than 30 mg/kg, we recommend sowing phosphorus with the seed. Often the cheapest sources of P are either MAP or DAP but do not consider the nitrogen from these fertilizers in your crop N budget.

Nitrogen fertilizer sown with the seed may give some initial boost to seedling vigour but does not increase grain yield. Wetting and drying of the soil associated with the flush irrigations leads to nitrogen transforming to a gas and being lost from the soil into the atmosphere.

It is recommended that extra phosphorus and zinc be sown with the seed in areas that have had topsoil removed during landforming operations. Soils deficient in zinc have been found to have problems with seedling survival when permanent water is applied (Beecher and Dunn, 2012).

Further Reading You can view the full report by clicking here.

November 2012