Remove soil constraints and lift yield


A new analysis shows overcoming a severe soil constraint that suppresses crop production and grain yields can be economic in most areas of the Western Australian grainbelt.

Findings from this research, conducted by CSIRO and the Department of Primary Industries and Regional Development with Grains Research and Development Corporation investment, will be presented at the Updates.

The CSIRO and DPIRD team used soil moisture probes and amelioration tactics, including deep ripping, at sites right across the WA grainbelt to help quantify the financial benefits of fixing soil constraints.

Soil constraints such as soil acidity, compaction, sodicity and salinity can lead to significant grain yield losses in WA crops.

At the GRDC Grains Research Update, Perth, CSIRO senior research scientist Phil Ward will outline findings from the field trials at Wubin and Dandaragan, where soil water data from seasons 2015, 2016 and 2017 was combined with Agricultural Production Systems sIMulator crop modelling data.

Dr Ward said the key results from these sites, which were also supported by the local West Midlands Group and Liebe Group, included:

Crop water use and yield responses to subsoil amelioration vary widely.

A driving factor for crop response is distribution of rainfall in the growing season.

Total growing season or pre-season rainfall is not as important as distribution.

Economic responses are common where a severe soil constraint can be fully overcome.

Partial amelioration (typically achieved by growers on-farm) will provide a one-year positive return in the majority of situations (for severe constraints).

Dr Ward said deep ripping to loosen compact soils and incorporate ameliorants, such as lime or gypsum, to improve fertility and soil structure had become an accepted farming practice in many parts of WA.

But he said research and experience was finding that crop responses to deep ripping could vary depending on the initial level of constraint from subsoil conditions and the seasonal conditions after treatment.

Dr Ward said costs of subsoil amelioration could also vary greatly, depending on the soil type and tactics used.

“The key to deciding whether to spend money on soil amelioration is to accurately determine the initial level of constraint imposed by the soil,” he said.

“Growers can get an indication of the level of their soil constraint by comparing actual yields with potential water limited yields.

“A severe constraint can result in actual yields being less than half of what is potentially achievable, which might provide impetus for growers and advisers to consider tactics that will address the problem.”

For its economic analysis, the CSIRO and DPIRD research team used an average cost of $100 per hectare for deep ripping.

“This meant in a one-year period and at a wheat price of $250 per tonne, the crop yield increase after treatment needed to be at least 400kg/ha for this tactic to be profitable,” Dr Ward said.

“Where the original soil constraint was severe and then fully overcome, this level of yield increase occurred in almost all seasons.

“But where the constraint was less severe, the required yield increase was obtained in 75 per cent of years, according to our modelling.

“Of course, yield increases are likely over more than one year, but a rapid return on investment helps to reduce the risks associated with soil amelioration.”

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