The DAN2203 Limited Water Decision Support project (LWDS) assessed the use of partial irrigation within the Australian cotton industry. The project sought to identify the extent and methods used that maximise the returns on water resources. It investigated the challenges for sustainable water management in the face of increasing production and business risks due to unpredictable rainfall and a variable water supply.

The scope of the technical report includes an assessment of partial irrigation practices where the crop’s evapotranspiration demand is not fully met with irrigation water. It provides an analysis of strategies employed by growers to effectively manage limited water resources and it discusses strategies used to maximise bales per megalitre or gross margin ($) per megalitre rather than bales per hectare.

The Australian cotton industry is confronted with the dual challenge of enhancing production and profitability while managing finite water resources. The unpredictability of water supply, exacerbated by climate change, poses significant risks to both growers and the industry. Partial irrigation is a practice adopted most commonly in response to low water availability such as drought. It can also be adopted by growers to maximise returns from available water.

Over the last 30 years, growers have adopted key strategies to manage irrigation water in periods with low availability. These strategies include water budgeting, strategic water application, and agronomic management such as field and row configuration, variety selection, and fertiliser management. Whilst there is evidence that water productivity can be improved by reducing the water applied per hectare without significant yield penalty, results are confounded by water use efficiency measures, the variation in the volume of water applied and row spacings. Additionally, there is little consistency in the terminology used to describe irrigation tactics to maximise water productivity.

In conclusion, partial irrigation is currently a minor subset of irrigated cotton systems that is mostly used by growers when water supply is reduced. The practice varies between growers depending on their farm and situation. Growers and their advisers may prefer to do what they are familiar with and know to do well (i.e., full irrigation). This may seem like a less risky or stressful decision, and avoid the extra complexity, decision making and risk of partial irrigation. The decision is to grow less area with more water, or plant a larger area and cut out area if there is insufficient water.