DOI: 10.7291/d1kd69
title: Saccharum spontaneum biomass and associated soil and foliar nutrient data

description: Invasive C4 grasses that colonize tropical landscapes abandoned from use
 for intensive grazing and agriculture can inhibit natural regeneration of
 secondary forest. In Panama, dense stands of Saccharum spontaneum require
 active forest restoration to re-establish successional processes. In this
 region, restoration strategies typically involve clearing grass cover and
 applying fertilizer prior to planting tree seedlings. However, if
 fertilizers alleviate nutrient limitation in the grasses and enhance their
 competition with tree seedlings, it can add to costs for manual
 maintenance of the sites free of Saccharum. Here we evaluated how S.
 spontaneum responds to nitrogen and phosphorus addition in the field to
 determine whether S. spontaneum is nutrient limited in this system. S.
 spontaneum was both nitrogen and phosphorus as revealed through increased
 foliar nutrient concentrations. S. spontaneum biomass was significantly
 greater in both nitrogen and phosphorus addition plots after both the
 first growth period (early rainy season) and second growth period (late
 rainy season), with release from co-limitation of N and P, and the overall
 impact of N, greater during the second growth period. Nutrient limitation
 in S. spontaneum and seasonal shifts in resource allocation suggest
 caution when fertilizing areas under restoration that were previously
 dominated by exotic grasses.
description: This experiment consisted of
 twelve blocks, each with four nutrient treatments:  no nutrient addition
 (control; C), N addition (N), P addition (P), and N+P combination (N+P).
 Plots were 5 x 5 m<sup>2</sup>, with a 2-m buffer between
 plots within a block, and a 3-m buffer between blocks. Dry fertilizer was
 added by hand after clearing <em>S. spontaneum </em>in July.
 Nitrogen was added as urea
 ((NH<sub>2</sub>)<sub>2</sub>CO<sub>2</sub>), and phosphorus was added as triple super phosphate (Ca(H<sub>2</sub>PO<sub>4</sub>)<sub>2</sub>•H<sub>2</sub>O). Nutrient application corresponded to 125 kg<sup> </sup>ha<sup>-1</sup> N and 50 kg<sup> </sup>ha<sup>-1</sup> P, as recommended for this region.  Nutrients were applied after clearing the site in July and again in October, after the first biomass harvest. Soil cores were taken at the end of the study (December) from each plot to compare final soil nutrient availability across treatments. We assessed <em>S. spontaneum</em> performance, in terms of density and above-ground biomass, in September and December 2011. Additionally, in December we collected soil and leaf nutrient data to compare nutrient treatments. We randomly collected and homogenized 10 soil cores at 10-cm depth for each plot; a 20-g subsample was used to extract soil nitrogen and another for phosphorus. We followed the KCl and Mehlich standardized protocols to extract available nitrate (NO<sub>3</sub><sup>-</sup>), ammonium (NH<sub>4</sub><sup>+</sup>), and phosphate  (PO<sub>4</sub><sup>-2</sup>). Soil samples were placed directly into solution in the field and processed in the lab within 24 h of being collected. For plant tissue nutrient analysis, we collected the third mature leaf from the base of 15 randomly selected individuals in each plot. Leaves were dried for 3 days at 60<sup>o</sup>C, and samples were processed at the University of California Santa Cruz. Five leaves were selected from each plot and leaf N and P were extracted following the Kjeldahl acid digestion protocol using a Lachat BD 46 block digester (Lachat Instruments, Milwaukee, WI USA).
description: Data are in a .csv file that can be opened with any spreadsheet
 or R.