The 2012 ASHS Annual Conference

The 60 year old date palm industry in the Southwest Arizona region has been established with the ‘Medjool’ cultivar rather than the traditional ‘Deglet Noor’ cultivar.  Palms are increasingly irrigated using low-volume irrigation rather than border flood method, and many new trees are planted in sandy soil rather than in silty loam soil.  There are no recommended nitrogen fertilization guidelines for non-bearing ‘Medjool’ dates.  In a 30-month study, we fertilized 1 to 3 year old palms with annual N rates ranging from 0.1 to 1.6 kg/tree for the first year, increasing to 0.3 to 2.94 kg/tree for the third year.  We also provided 4 to 6 year old non-bearing palms with constant annual N rates ranging from 0.4 to 3.6 kg/tree.  For the 1 to 3 year old palms on drip irrigation on sandy soil, initial rates of 0.4 kg increasing to 1.46 kg led to a final growth rate of about 6 cm/month, while the trees provided with 0.1 kg N in year one and increasing to 0.3 kg N in the third year grew had a final growth rate of only 5 cm/month.  For 4 to 6 year old trees on the same soil and irrigation regime, an annual N rate of 1.2 kg/tree led to a final growth rate of at least 5.5 cm/month, and application of 3.6 kg N led to a 6.6 cm/month growth rate, compared with only 5.25 cm/month growth rate for the palms supplied with 0.4 kg N annually.  For 1- to 3-year-old palms irrigated using border flood and planted in silty loam soil, initial N rates of 0.8 kg increasing to 2.13 kg in the third year led to an final growth rate of about 7.5 cm/month, while the trees provided with 0.1 kg N in year one and increasing to 0.3 kg N in year three had a final growth rate of only 6.5 cm/month.  For 4 to 6 year old trees on the same silty loam soil and flood irrigation regime, an annual N rate of 1.2 kg N led to a growth rate of as much as 10.2 cm/month, compared with only 8.6 cm growth per month for the palms supplied with 0.4 kg N annually.  Leaf N concentrations generally reflected growth rates.  This work will help to provide ‘Medjool’ date palm growers with accurate guidelines for N fertilization of non-bearing date palms.