The Effect of Form, Rate, and Position of Phosphatic Fertilizers on Growth and Nutrient Uptake of Sitka Spruce on Deep Peat

The effects of superphosphate, ground rock phosphate, and basicslag, each applied in three positions, on the growth of Sitkaspruce (Picea sitchensis Carr.) were compared up to the eighthyear after planting on deep oligotrophic blanket peat in NorthernIreland. Broadcast application was initially the most effective,but after eight years there was no significant difference inmean tree height between this method and placement on top ofthe planting ribbon. Application of fertilizer below the ribbongave consistently poorer results but with the previously usedmethod of placement in the planting hole growth was almost 40per cent less even than this. At equivalent rates, superphosphateand ground rock phosphate were equally effective and both weresignificantly better than basic slag. Fertilizer position had little effect on foliar nutrient concentrationin either the fifth or eighth growing seasons. In both seasons,foliar N concentration increased with amount of slag appliedbut N levels were higher with superphosphate and G.R.P. in boththe fifth and eighth seasons. At the lower rates of appliedslag, foliar N concentrations were below the accepted optimumin the eighth season. Foliar P concentration also decreasedsignificantly with time and, except where 100 Kg P per ha hadbeen applied as slag, the P nutrition of the trees after 8 yearswas becoming critical. Fertilizer treatment had no significanteffect on foliar K concentration in the fifth season but bythe eighth season foliar K levels were inversely related togrowth rate. This suggests an imminent K deficiency. It is concluded that the broadcast application of ground rockphosphate at not less than 50 Kg P per ha is an effective fertilizerregime for the establishment of Sitka spruce on deep blanketpeat, but that supplementary fertilizing with K, and possiblyP, may be necessary about 8 years after planting.