An assessment method to gauge the water-use efficiency of a plant and drought resistance of a farm
Why is it that the field on the left (below) has a greater resistance to a severe drought than the adjacent field on the neighbouring farm on the right?
Why is it that the same field (below left) is able to recover quicker and better than the neighbouring field on the right?
Photos: Courtesy of R McLean
Why is it that this field can have good green pasture growth despite receiving only 105 mm RF in 5 months
(Oct 2013 - Feb. 2014)?
Workshop assessing the characteristics of this drought prone soil and the management options required to increase its drought resistance
Soil moisture deficits and prolonged dry periods severely limit farm productivity and the financial margins a farm can make per hectare. With the changing weather patterns and increasing occurrence of droughts and subsequent soil moisture deficits, it is timely to look at a number of ways to reduce the severity of droughts on farm by increasing the water-holding capacity of the soil and the ability of the plant to more efficiently utilise the moisture in the soil.
We are now growing twice as much food but require three times as much water to do it.
While there is no substitute for good soil moisture levels, there is much that can be done to increase the water-use efficiency of a plant and the drought resistance of rain-fed farms. To reduce the effect of a drought and increase the resistance of a pastoral and cropping farm to drought conditions, there are 20 key measures that farmers can address to increase drought resistance. These key factors provide a Drought Resistance Index (DRI) of whether a field is likely to have a high, moderate or low resistance to dry conditions and importantly what can be done about it. Unlike soil texture, aspect, climatic zones, weather patterns etc., the 20 indicators are dynamic and as such are influenced by soil condition, management and land use.
The 20 key factors provide the basis of a quick and easy to use scorecard for both pasture and cropping but also apply to other plants. Anyone of the indicators affects the resistance of a field to drought but collectively, the 20 factors have a significant influence on the water-use efficiency of a plant and the drought tolerance of a farm. As such, addressing the 20 factors can also significantly reduce the amount of water that is applied by irrigation, saving water and pumping costs. The Drought Resistance Scorecard (DRS) requires about 20‒25 minutes to complete in the field.
Each of the indicators is scored according to rating scales and comparative photographs provided. As the farmer/grower scores each indicator, it becomes immediately apparent what factors are limiting the water-use efficiency of a plant, the water-holding capacity of the soil and a farms resistance to drought, and what specific ameliorative aspects need to be addressed. This leads to the management decisions required to increase a plant’s water-use efficiency and the drought resistance of a field. The 20 indicators include soil structure, root density, rooting depth, eight soil chemical and five biological properties, soil carbon, the amount and form of fertiliser and nitrogen used, the percentage cover by drought resistant species, and pasture residual levels. The indicators for cropping are similar except the pasture specific factors are replaced by the Method of Cultivation and Percentage Ground Cover.
A workshop on the Drought Resistance Index and what makes a plant more water efficient entails a 90 minute powerpoint seminar where each of the 20 drought resistant indicators and the science that underpins them are presented and discussed. This is followed by a practical exercise in the field filling out the scorecard and addressing the management options required to develop a more water efficient plant and raise the drought resistance of a farm.
While the Drought Resistance Index, i.e. the total score gives an overall assessment of the water-use efficiency of a plant and whether a field has a high, moderate or low resistance to dry conditions, the individual scores of each indicator provides the basis of an action plan as to what needs to be addressed and the management practices required to increase drought resistance and the production performance of the farm. Any indicator scoring 1 or less needs to be looked at as to what can be done to raise the score.
The main purpose of the workshop is to 1) address those factors that promote the water-use efficiency of a plant; 2) address those factors that increase the water-holding capacity of the soil; 3) assess the drought potential of a field, and 4) develop an action plan to help mitigate the effects of a drought. Because of seasonal, logistic and budget constraints, not all 20 indicators can necessarily be addressed straight away. It is therefore a matter of determining what are the indicators that are scoring the lowest and what needs to be looked at in the first instance to lift their score and therefore production.
Like the Visual Soil Assessment (VSA) method I wrote, the Drought Resistance Scorecard incorporates a number of visual soil indicators but also requires management input and information from soil and herbage tests. To complete the field exercise, the course participants receive a six page handout of the scorecard and the defining drought resistance rating scales and comparative photographs of each indicator. A report on the scorecard and the recommended management options to raise the drought resistance of the field is also given post workshop. This includes a discussion of each of the 20 indicators and an action plan to lift any underperforming indicators of drought resistance.
Drought resistance seminar, Geelong, VICTORIA