Sensitivity of yield determinants to potassium deficiency in 'Nonpareil' almond (Prunus dulcis (Mill.) DA Webb)

The objective of this multi-year study was to generate data linking potassium (K) deficiency to almond (Prunus dulcis (Mill.) D.A. Webb) productivity. A range of tree K status (as indicated by leaf K concentrations) which encompassed the currently-accepted K deficiency/sufficiency range was established to assess the relative sensitivity to K deficiency of yield components (flower number, percentage fruit set, fruit size, and spur mortality) and to establish the time frame between the onset of K deficiency and yield reduction. Although large, statistically-significant differences in leaf K concentrations were detected in the year following the start of differential K fertilizer application, yield was not affected significantly until the third growing season (i.e. two years after the start of differential K fertilizer applications). Inadequate K-availability did not affect percentage fruit set or fruit size. Spur mortality following fruit maturation was (highly) significantly increased on fruit-bearing spurs relative to vegetative spurs, but there was no evidence of an independent effect of K availability on spur mortality. Potassium-deficient spurs exhibited reduced flowering in the subsequent years. Effects of K-deficiency are likely to be cumulative, and especially pronounced following years of heavy cropping. There was a good linear correlation (R = 0.60, P = 0.0050) between leaf K concentration in 1999 and yield in 2000.