Growth and Nutrient Uptake of Irrigated Young Ponderosa Pine After Fertilizer Treatments
1966
Tarrant, Robert F. | Silen, Roy R.
Ammonium nitrate and treble superphosphate were applied to irrigated, 7-year-old ponderosa pine (Pinus ponderosa Laws.) in a wind break planted on Deschutes sandy loam in central Oregon. Nitrogen was supplied at levels of 0, 200, and 400 lb/acre and P at 0, 100, and 200 lb/acre in a factorial experiment. Fertilizer treatments were repeated two years after initial application. Over a 6-year period after first fertilizer treatment, tree growth was stimulated in relation to amount of N applied singly. When N and P were applied together in various combinations, growth was in some cases stimulated and in other cases reduced, according to the combination of the two elements. Foliage N concentration was not affected significantly by any treatment, but when P was applied at the 100-lb rate, addition of N treatments caused a linear increase in foliage N concentration. With P at 200 lb, addition of N caused a linear decrease in foliage N concentration. At the conclusion of the study, N content of soils receiving the heaviest N fertilizer application was only about 11% more than that of the controls. However, under heaviest P treatments soil P was more than five times that of unfertilized soils.
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