Effects of salinity and applied water on yields of ‘Hass ’ avocado on Mexican seedling rootstock.

A field experiment in a commercial orchard of mature ‘Hass ’ avocados on Mexican seedling rootstock (Persea americana) was conducted between 1992 and 1997 to determine how yield was influenced by the amount of irrigation water applied and the frequency of application. Three amounts of applied water (targeted at 90, 110 and 130 % of estimated crop evapotranspiration) were applied at three frequencies (one, twice and seven times per week). The electrical conductivity and chloride concentration of the irrigation water, corrected for rain, were 0.7 dS·m-1 and 1.8 mmol·L-1 (65 mg·L-1), respectively. Irrigation treatment did not influence the average salinity in the rootzone, leaching fraction, and chloride concentrations in leaves. A maximum soil water salinity of about 4 dS·m-1 occurred in the lower portion of the rootzone for all irrigation treatments. Trees irrigated seven times per week had lower yields than those that received less frequent irrigation. Yields increased with increasing amounts of applied water during the last two years of the experiment. The influence of the amount of applied water and soil salinity on avocado yields and leaching fractions for treatments irrigated once and twice a week was explained using production function concepts. The threshold salinity above which yield decline occurred was determined to be 0.57 dS·m-1 and yield declined by 65 % per unit of salinity above the threshold. Our results suggest that maximum yields of ‘Hass ’ avocado on Mexican seedling rootstock are not achievable when the average annual salinity of irrigation water, including rainfall, is greater than about 0.5 dS·m-1