The 2012 ASHS Annual Conference

Besides the effect of alternate bearing to decrease yield in Off years, alos low nut yield in pecans growing under subtropical regions had occurred in seasons preceded by winters with very low chilling accumulation. Also, alternated periods of warm and cold conditions during dormancy are common and its effect on nut yield is unknown. The objective of this study was to determine the effect of weather during dormancy on commercial pecan nut yield. The effects of temperature, relative humidity and precipitation of November, December, January, and February on commercial nut yield of pecans growing under subtropical conditions were examined by linear regression analysis. Growing area studied has an elevation of 70 m and it is located in Northwest México between 28°N and 29°N and 111°W and 112°W. Using a temperature base of 7.2 °C, from November 1 to February 28, chilling hours ranged from 142 in “warm winters” to 232 in “cold winters”, in a 10 years span (1999–2009). Independent variables were the average and the standard deviation (SD) of daily chilling hours (base temperature 10 °C, minus hours above 25 °C), daily high temperature, daily low temperature, daily average temperature, daily range temperature, and daily relative humidity. Also cumulative precipitation was included. Period from November 1 to February 28 was divided by month (November, December, January, and February), bimonthly (November + December, December + January, and January + February), and for the whole period (November 1 to February 28). The only significant effect was found with the standard deviation of the February Chilling (kg/ha= 105.8 + 439 · SD February daily chilling; r²= 0.53*) and the standard deviation of the February daily minimum temperature (kg/ha= -104.8 + 680.8 · SD daily low temperature; r²= 0.47*). No significant responses were detected for precipitation and relative humidity. The higher the variation in daily chilling hours and minimum temperature represent the presence of periods of cold and warm days. According data, dormancy stage during February seems to be more sensitive period to temperature.