Effects of Fertilizer Nitrogen on Tree Growth, Foliar Nitrogen, and Herbage in Eastern Cottonwood Plantations

When five rates of nitrogen fertilizer (0 to 672 kg! ha) were tested in two eastern cottonwood (Populus deltoides Bartr. ) plantations 7 and 10 years old in the Mississippi River floodplain , first season volume growth was more than doubled by fertilization . By the end of the third season, the direct effect of fertilization had apparently disappeared although a volume advantage caused by the large initial response was still evident. In one plantation, volume growth for the 3 years after fertilization was greatest at 336 kg Nt ha , and in the other volume growth was greatest at 672 kg NI ha. However , lower rates gave more volume growth per unit of applied N. Fertilizer also increased the N content of herbaceous plants. Additional Index Words: Populus deltoides Bartr., fertilization, volume growth, ammonium nitrate, herbaceous N, herbaceous biomass, N ITROGEN DEFICIENCY is an important problem on m a ny old-field soil s in the Mississippi River floodplain (B lackmon and Broadfoot, 1969; Blackmon and White , 1972). Studies have demonstrated that eastern cottonwood (Populus dellodies Bartr.) growth can be st imulated by fertilization with 168 kg of nitrogen/ ha from ammonium ni trate (B lack mo n and White, 1972) . Less is known , how ever, about the re ac tion of cottonwood plantations to various leve ls o f applied nitrogen. This paper describes tree and herbage response to several rates of N applied to two esta blished cottonwood plantations in the Miss iss ippi River floodplain. I A portion of this paper was presented be fore Div . S-7 of th e Soil Sc ience Society of America at the 65th an nua l meeting of the American Society of AgronolllY. Las Vegas, NV . 11 16 Nov. 1973. Received 27 Jan . 1977 . Approved 10 May 1977 . ' Principal Soil Scientist, Southern Hard woods Laboratory. maintained at Stoneville. MS ~8776 , hy the Southern Forest Ex p. Stn .. Forest Se rvice-US DA, in cooperation with the Missi ssippi Agric ultural and Forestry Exp . Stn . and the Southern Hardwood Forest Research Group.