Plant and Soil 114. 39-43 (1989) ('~ 1989 Kluwer AcademicPublishers. Printed in the Netherlands PLSO 7818 Recovery of 15N-labelled fertilizer by Coastal bermudagrass in lignite minesoil J. G. SKOUSEN, C. A. CALL and R. W. WEAVER Texas A & M University, College Station, TX 77843, USA Received 24 May 1988. RevisedOctober 1988 Key words: ammonium sulfate fertilizer, Coastal bermudagrass, clipping, N distribution, NH4-fixation, overburden, revegetation, Texas lignite minesoil Abstract Minesoils developed from lignite surface mining in Texas are nutrient-poor and have a high N retention capacity. A major concern of landowners and soil conservationists is the response of Coastal bermudagrass to the application of low rates of ammonium-N fertilizer on these nutrient-poor minesoils. A glasshouse study, using mSN-labelled ammonium sulfate fertilizer and lignite minesoil, was conducted to measure Coastal bermudagrass biomass production and fertilizer recovery during establishment in response to clipping at 2, 4, and 8 week intervals. At N rates of 0, 40, and 80 kg N ha-~, increases in N fertilization increased Coastal bermudagrass aboveground biomass 5-fold, but showed only small increases in belowground biomass. Recovery of ammonium-N fertilizer ranged from 54 to 63%. Roots contained approximately the same N content across all fertilizer rates suggesting that young, establishing, Coastal bermudagrass roots reserve N until their N requirement is met. As more N is obtained above that which was needed to maintain roots, then additional N taken up by the plant was transported to aboveground plant parts for growth. Frequent clipping intensified N transport to aboveground tissues. Reduced amounts of N were contained in roots after clipping due to reductions in root growth, biomass, and resource demand. Fertilization of Coastal ber- mudagrass at low N rates with different N fertilizer forms influenced the distribution of N in the plant and affected N recovery by different parts of the plant. Introduction Coastal bermudagrass (Cynodon dactylon) is the most commonly used forage species for revegeta- tion of lignite surface-mined land in east central Texas because of its high yield potential, rapid surface coverage, and efficiency of nutrient use under high fertilization regimes (Burton et al., 1985). Recent research (Brown et al., 1983; Hons et al., 1979) indicates that the root biomass of Coastal bermudagrass on reclaimed minesoils in Texas is approximately three times greater than that obser- ved on unmined soils. Mixing topsoil with overbur- den materials during mining in this region of Texas results in higher silt and clay contents in the new surface horizon, with associated increases in water- holding capacity and cation exchange capacity (Dixon et al., 1980). Due to differences in root 39 biomass and soil properties between mined and unmined lands, fertilizer rates for forages grown on native soils are probably not applicable for forage production on mined lands. Furthermore, fertiliza- tion studies with forage grasses reveal the N applied to minesoils is less available for plant uptake than the same amount of N applied to adjacent native soils (Hons and Hossner, 1980; Reeder and Berg, 1977). Minesoils in east central Texas are reported to have a large ammonium fixation capacity (Hons and Hossner, 1980), with as much as 68% of N being tied up when applied as ammonium-N fer- tilizer. When fertilized at 336kgNha ~ and 269 kg P ha- 1, Coastal bermudagrass utilized both the nitrate and ammonium forms equally and produced essentially the same yields on minesoils (Hons et al., 1980). However, at fertilizer rates of 112 kg N ha- t and 134 kg P ha- i, the nitrate form