Research quantifies benefits of summer rainfall

Author: Natalie Lee | Date: 05 Mar 2013

Black sky  with a light brown field

Moisture will be stored in the subsoil and potentially lead to higher yields in the subsequent grain crop if more than 25 to 30mm is received in a single summer rainfall event.

While crop residue on the surface of paddocks plays an important role in preventing wind and water erosion, it has little impact on the amount of water stored in the soil from summer rain.

CSIRO senior researcher Phil Ward told the Agribusiness Crop Updates that these were some key findings from recent Western Australian research supported by the Grains Research and Development Corporation (GRDC).

The research included crop simulation modelling studies and projects conducted under the GRDC Water Use Efficiency Initiative, and involved a number of stakeholders including CSIRO, the WA No-Tillage Farmers Association (WANTFA) and the Liebe Group.

Dr Ward said studies had shown that a rainfall event of 25mm or less generally evaporated prior to sowing, regardless of when it fell between November and the start of the following growing season (May 1).

“Even if a grower received 25mm of rain on April 15, there would only be 7 or 8mm of moisture left in the soil by the start of May, which is obviously beneficial and provides an opportunity for seeding, but is less than growers might have thought,” he said.

CSIRO researcher Phil Ward with a soil moisture probe

CSIRO researcher Phil Ward with a soil moisture probe.

But Dr Ward said that if more than 25mm of summer rainfall was received at one time, moisture would be retained for extended periods in the subsoil, especially on sandier textured soils which tended to lose less water to evaporation.

“For example, a rainfall event of 100mm would leave about 70mm in the soil, with later rainfall being more beneficial,” he said.

Dr Ward said increased soil water at sowing could lead to higher crop yields, particularly on soils with higher soil water capacity or in dry growing conditions.

“In sandy soils, retained soil moisture from summer rainfall will be useful usually only in dry growing seasons, as these soils have limited water holding capacity,” he said.

Dr Ward said that while crop residue management was not likely to influence stored soil water, it did reduce the risk of wind and water erosion and decreased evaporation rates for a few days after a rainfall event.

“Crop residue may therefore be beneficial in extending the sowing opportunity for a grower following breaking rains,” he said.

Dr Ward said that while research had produced data about how much summer rainfall was retained in different soil types, the degree to which summer weeds affected soil water and crop yields was less clear.

“However, research has shown that summer weeds are effective scavengers of soil water and nitrogen, and that summer weed control usually provides a positive economic return,” he said.

“Modelling studies in WA’s Northern Agricultural Region suggest that, on average, soil water storage on May 1 is reduced by about 10mm if summer weeds are not controlled.

“The effect of summer weeds on soil water storage varies considerably from year to year depending on the amount of rainfall received and where it falls.”

Perth’s Agribusiness Crop Updates, held on February 25 and 26, were supported by the GRDC and the Department of Agriculture and Food (DAFWA).

The GRDC’s five-year $17.6 million Water Use Efficiency Initiative was established in 2008 with the aim of lifting the water use efficiency (WUE) of grain-based production systems by 10 per cent across Australia’s southern and western cropping regions.

Findings from research conducted under the initiative are outlined in the new Water Use Efficiency supplement included in the March-April edition of the GRDC magazine Ground Cover and available for free download at


CAPTION: A wet summer provides an opportunity to store water, and perhaps nitrogen, in the soil for improved crop growth in the subsequent growing season.

CAPTION: CSIRO researcher Phil Ward with a soil moisture probe.

For interviews:

Phil Ward, CSIRO
(08) 9333 6616


Natalie Lee, Cox Inall Communications
(08) 9864 2034

GRDC Project Code CSP00127, CSP00128, LIE00006

Region West