Soil carbon and nutrients in a coastal Oregon Douglas-fir plantation with red alder
Cromack, K.J.; Miller, R.E.; Helgerson, O.T.; Smith, R.B.; Anderson, H.W.
Soil Science Society of America Journal 63(1): 232-239
ISSN/ISBN: 0361-5995 DOI: 10.2136/sssaj1999.03615995006300010034x
Carbon and nutrients in the forest floor and mineral soil were measured to determine amounts and variation among eighteen 0.081-ha plots in a Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] plantation growing with volunteer red alder (Alnus rubra Bong.). Ten years earlier, the preceding mature conifer stand was clearcut and nearly all logging slash and forest floor were consumed by slash fire. Forest floor mass in the 9-yr-old plantation averaged 9.86 Mg ha-1, with 3.71 Mg C, 98.0 kg N, 10.6 kg P, and 8.4 kg S ha-1. Mineral soil to 1-m depth averaged 176 Mg C, 8330 kg N, 3340 kg P, and 605 kg S ha-1 in the <2-mm fraction. The 2- to <6-mm soil fraction averaged an additional 100 Mg C, 4480 kg N, and 1700 kg P ha-1. Net mineralizable N as NH4 (anaerobic N mineralization index) totaled 99 kg N ha-1 in the top 45 cm of the mineral soil and 62 kg N ha-1 in the 45- to 100-cm depth. Density fractionation showed that the light fraction (<1.65 Mg m-3) was only 13.4% of the fine soil mass of the 0- to 15-cm depth, yet contained about 40% of the total C and N capital in the <2-mm size fraction. The substantial amounts of C and nutrients in this low-bulk density soil (<2-mm fraction, 0.30 Mg m-3) indicate a fertile soil despite large previous losses of organic matter and N from the site. Reprinted by permission of the publisher.