A graphical method to evaluate irrigation water application uniformity

Drought reduces pasture production. Irrigation can be an effective response, but apply too little water and pasture production will be less than the well-watered potential. Apply too much and nutrients can be leached, reducing soil fertility and pasture production. For the right amount of water, application should be uniform across the irrigated area. To evaluate irrigation water application uniformity, we developed a graphical method to analyse measurements along linear transects. By plotting the data, variable results were readily identified as well as potentially systematic patterns. The plot was divided into quadrants and the observations in each quadrant counted. For a random spatial distribution, one-quarter of the measurements were expected in each quadrant. The observed and expected counts were compared using a chi square statistical test. To illustrate, we analysed measurements made on eleven irrigated farms and contrasting hypothetical situations. The results and conventional distribution uniformity calculations will be discussed.