Percent light penetration: 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.

本实验为新建样地实验，选址于E026园区旁。该实验样地包含源自北美草原生物群区的主要禾本科物种单一种植群落，同时还设置了3种豆科植物样地（E070）。本实验的设计与目标与E026实验相似，仅样地规模更大。
本实验的基础设计为：在14种不同配比的土壤基质上，分别开展植物单一种植及多种竞争组合种植实验。实验场地使用推土机移除了30英寸厚的表层土壤，随后向每个样地添加厚度介于0.3英寸至10英寸之间的黑土。土壤总有机碳含量范围为0.1928%至5.63134%，总氮含量范围为0.0158%至0.4591%。各试验样地所添加黑土的精确用量详见田间作业记录。
每年5月初与6月末，各试验样地会被施加等量的硫酸镁（MgSO4）、碳酸钙（CaCO3）、五氧化二磷（P2O5）及氧化钾（K2O）。更多相关信息可查阅施肥方案细节。每种土壤基质对应26个副样地，其中副样地24、25、26现已归入实验70。
每个副样地尺寸为1.2 m × 1.2 m，对应唯一的处理组。因此，在同一种土壤基质中不存在重复的处理组。本实验实为回归实验，其回归变量为实验设置的土壤总氮含量梯度。播种当日，各试验样地会施加磷（P）、钾（K）、钙（Ca）、镁（Mg）及微量金属元素混合肥。
试验样地种植了以下物种的不同组合：小须芒草（Schizachyrium scoparium，SS）、大须芒草（Andropogon gerardi，AG）、格兰马草（Bouteloua gracilis，BG）、柳枝稷（Panicum virgatum，PV）、史密斯冰草（Agropyron smithii，AS）、野牛草（Buchloe dactyloides，BD）及加拿大一枝黄花（Solidago canadensis，SC）。播种工作于1989年5月23日至25日完成。加拿大一枝黄花未萌发，因此后续改用椭圆叶栎（Quercus ellipsoidalis，QR）种子进行补植。
实验区域周边设置了地下防囊鼠围栏（深度3英尺，宽度1英尺）与地上防啮齿类/鹿类围栏（高度6英尺）。在整个生长季期间，实验样地均会进行灌溉，以避免水分成为生长限制因子。定期在植被上方与下方开展光照强度测定；定期采集土壤样本以检测铵态氮与硝态氮含量，并采集地下生物量样本；同时定期刈割地上生物量样本，经过分拣后称重。