Nutritional concerns in selection of black cottonwood and hybrid clones for short rotation

Abstract

Nitrogen in leaf fall and in aboveground tissue of close-spaced 4-year-old clones of black cottonwood (Populus trichocarpa Torr. and Gray), Populus trichocarpa .times. Populus deltoides Bartr. hybrids, and a ''Robusta'' clone was determined. Phosphorus and calcium in the harvested material were also determined. Dry weight of leaf fall varied from 4.4 to 6.6 Mg ha-1 year-1 and it contained from 62 to 84 kg N ha-1. Estimated annual uptake of N in aboveground biomass and leaves ranged from 95 to 276 kg N ha-1 and was largely related to clonal productivity. Aboveground dry weight of woody biomass at the end of 4 years varied from 29 to 111 Mg ha-1 with the two trichocarpa .times. deltoides hybrids being the highest producers. Nutrients contained in aboveground woody biomass differed greatly among clones in this study, ranging from 95 to 420 kg N ha-1, 14 to 105 kg P ha-1, and 80 to 288 kg Ca ha-1. The N and P utilization efficiency of clones ranked as follows: black cottonwood > new hybrids > ''Robusta''. For Ca, the ranking was as follows: black cottonwood = new hybrids > ''Robusta''. From the standpont of nutrient-use efficiency, as well as high yield, rooting of cuttings, sprouting after harvest, and other desirable features, black cottonwood offers clear advantages to be captured in breeding programs for short-rotation culture.