Optimization of nitrogen and potassium nutrition to improve yield and yield parameters of irrigated almond (Prunus dulcis (Mill.) D. A. webb)

An experiment was conducted to evaluate the effect of nitrogen (N) and potassium (K) fertilization rates and fertilizer sources on almond yield and yield related parameters- fruit and kernel weight, number of fruits per tree, crackout percentage and leaf nutrient status by individually monitoring 768 trees. The experiment was carried out between 2008 and 2012 with four rates (140, 224, 309 and 392 kg N ha(-1)) and two sources (UAN and CAN) of N and three rates (112, 224 and 336 kg K ha(-1)) and sources (SOP + KTS, SOP and KCl) of K. Nitrogen fertilizer rate had a significant effect on yield in the second through the fourth year of the experiment. Tree yield was maximized at 18.5 kg and 23.7 kg kernel per tree in 2010 and 2011 season respectively when July leaf N was in the range 2.4-2.5% corresponding to an N application rate of 309 kg N ha(-1) and there was no increment in yield above 2.5% leaf N. Source of N had no significant effect on yield response. Potassium fertilization rate had no significant effect on yield while K sources had significant effect in 2010 only. Increasing N application resulted in lighter fruit, and kernel weight decreased with increasing N application under moderate yield conditions, and increased under high yield conditions. Yield increase with increasing N application was due to an increase in number of fruits and increased crackout percentage. Leaf K above 1% did not increase yield and there was no consistent effect of K supply and K source on yield parameters. There was a strong relationship between total yield and number of fruits per tree, which increased with increasing N application. Crackout percentage was also positively correlated to kernel yield. Nitrogen and potassium fertilization rate should be based on expected yield and tree N and K status. For a well productive mature orchard, N application of 309 kg ha(-1) with either UAN or CAN can meet crop N needs. K fertilization should consider K contribution from soil. Under condition of 100-150 mg kg(-1) soil exchangeable potassium, K application of 112 kg ha(-1) with any K fertilizer source can satisfy crop K demand.