Salinity and climatic effects on the yields of citrus

A multiple linear regression analysis of salinity and climate against yield of Valencia and Washington Navel Oranges was performed for the period 1945-79 on data from irrigated orchards in Sunraysia, Berri, Waikerie and Mypolonga. Principal component analysis was utilized to reduce the number of climatic variables introduced into the multiple regression analysis. High temperatures and high evaporation during flowering and fruit set (November and December) were associated with reduced yields in Sunraysia, Berri and Waikerie, possibly by increasing flower and fruit drop, and by reducing fruit set. At Mypolonga, the coolest location studied, high temperatures were associated with increased yields. Salinity was negatively associated with yield at Mypolonga, Waikerie and Berri, the locations of highest salinity. No effects were observed at Sunraysia. It was not possible to deduce a critical level of salinity in irrigation water that is associated with yield loss or the magnitude of yield loss from the statistical analyses. However, we did observe that salinity during the irrigation season prior to harvest was associated with decreased yields, while only at Mypolonga was salinity in the year of harvest a significant variable in the analyses.