Delaying rice water
From the November 2009 edition of Agriculture Today.
Marginally lower rice yield achieved by delaying permanent water has resulted in an 11 per cent advantage in water productivity, compared to yield from conventional irrigation treatment in a Yanco trial.
Growers have almost doubled water productivity of average NSW rice crops over the past 20 years.
After reducing water use by selecting non-leaky fields, growing shorter season and higher yielding varieties, and managing the crop to achieve maximum yield, the next best opportunity to increase water productivity appears to be delaying the application of permanent water.
Reducing the evaporation losses that occur from both the soil and exposed water surface in the period between the traditional time of permanent water application and when the rice crop canopy covers the ground or water surface enables water savings.
Industry and Investment NSW research agronomist, Brian Dunn, and CSIRO Sustainable Ecosystems researcher, Don Gaydon have been investigating the potential for saving water and improving water productivity by delaying the timing of permanent water application.
A replicated experiment was conducted at Yanco Agricultural Institute in the 2008-09 season, with water use, rice growth and yield, measured for a conventional drill sown crop and three delayed permanent water treatments.
Delayed permanent water treatments were flush irrigated at 40, 80 and 160 millimetres of cumulative evapotranspiration (ET) receiving 11, six and four irrigations respectively before permanent water was applied, prior to panicle initiation.
"Current rice varieties in our environment need deep water during the reproductive period to provide a buffer against potential grain yield loss caused by cold temperatures during pollen formation," Mr Dunn said.
The largest reduction in water use was achieved by the 160mm delayed treatment which used 16pc less irrigation water than the control.
Prior to permanent water, the 160mm treatment had fully exploited the moisture in the soil profile to 15 centimetres depth and the rice was showing symptoms of severe moisture stress.
The delayed permanent water treatments had much lower growth than the conventional treatment when measured early in the season.
The 160mm treatment had only half the dry matter of the conventional treatment before permanent water was applied, but by flowering there was no significant difference in dry matter between any treatments.
Rice grain yield of the conventional treatment was highest at 10.9 tonnes per hectare, followed by the 80mm and 160mm delayed permanent water treatments with 10.2 and 10.1 t/ha respectively.
The 40mm treatment yielded lowest at 9.2 t/ha, due to suspected nitrogen losses caused by many irrigations.
The irrigation water productivity of the 160mm treatment was 0.83 tonnes per megalitre, with the conventional treatment lower at 0.75 t/ML.
Although the grain yield of the 160mm treatment was 0.8 t/ha lower, the 2.3 ML/ha less water used to produce this yield resulted in 11pc advantage in water productivity.
"Historically weed control has been a problem for rice not grown under ponded conditions, but the use of currently available commercial herbicides provided excellent weed control in all treatments," Mr Dunn said.
"The cost of weed control must be constrained to conventional practice levels to maximise the economic benefit of the delayed permanent water practice."
The project funding was provided by Land and Water Australia, the Ricegrowers Association of Australia, Industry and Investment NSW and CSIRO.
Contact Brian Dunn, Yanco, (02) 6951 2621, brian.dunn@industry.nsw.gov.au
