Reproductive biomass: Plant Competition Under Different Nitrogen Levels:A Garden Experiment

This is the new garden plot experiment located next to the E026 gardens. This garden contains monocultures of major grass species from across the grassland biome of North America, and also 3 legume species (E070). The design and purpose are similar to E026, except the plots are larger. The basic experimental design consists of growing plants in monoculture and in various competitive combinations on each of 14 different soil mixtures. A bulldozer was used to remove 30 inches of top soil at the site. To each plot a certain amount of black dirt, ranging from 0.3 inches to 10 inches, was added. Total carbon ranged from 0.1928% to 5.63134% and total nitrogen ranged from 0.0158% to 0.4591%. The exact amounts of black soil added to each plot are described in the field operations.

Equal amounts of MgSO4, CaCO3, P2O5 \& K2O are added to the plots each year in early May and late June. For further information, see fertilization details. Each soil mixture has 26 sub-plots. Subplots 24, 25 and 26 are now part of experiment 70.

Each subplot, which is 1.2 m x 1.2 m, is a unique treatment. Thus, there are no replicates of a treatment within a soil mixture. Rather, the experiment is a regression experiment, with the regression variable being the experimentally-imposed level of total soil nitrogen. At the time the seeds were planted, each plot was fertilized with a mixture of P, K, Ca, Mg and trace metals.

The plots were planted with different combinations of the following species: Schizachyrium scoparium (SS), Andropogon gerardi (AG), Bouteloua gracilis (BG), Panicum virgatum (PV), Agropyron smithii (AS), Buchloe dactyloides (BD) and Solidago canadensis (SC). Seeds were planted on May 23-25, 1989. The Solidago canadensis did not germinate, so Quercus ellipsoidalis (QR) seeds were planted in its place.

A below-ground gopher fence (3 feet deep and 1 foot wide) and an above-ground rodent/deer fence (6 feet tall) was built around the area. The plots are watered throughout the growing season to keep water from becoming a limiting resource. Light readings were taken above and below vegetation. Soil samples for ammonium and nitrate and belowground biomass are periodically taken. A sample of aboveground biomass are clipped, sorted and weighed periodically.