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.本实验为新建样地实验，毗邻E026样地园区。该园区包含北美草原生物群区主要草本物种的单作栽培群落，同时设置了3种豆科植物样地（E070）。本实验的设计与研究目标与E026相似，仅样地规模更大。基础实验设计为：在14种不同土壤配比的样地中，分别开展植物单作栽培与多种竞争组合栽培实验。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英寸的黑土。样地总有机碳含量区间为0.1928%~5.63134%，总氮含量区间为0.0158%~0.4591%，各试验样地的黑土添加量详见野外作业记录。 每年5月初与6月末，向所有样地施加等量的硫酸镁（MgSO4）、碳酸钙（CaCO3）、五氧化二磷（P2O5）与氧化钾（K2O），施肥细节详见相关说明。每种土壤配比对应26个副样地，其中第24、25、26号副样地现已归入实验70。 每个副样地规格为1.2m×1.2m，对应唯一的处理组合，因此同一土壤配比下不存在重复处理。本实验属于回归设计实验，回归变量为实验调控的土壤总氮含量水平。播种时，每个主样地均施加磷（P）、钾（K）、钙（Ca）、镁（Mg）与微量金属元素混合肥料。 实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）与加拿大一枝黄花（Solidago canadensis, SC）。播种时间为1989年5月23日至25日。因加拿大一枝黄花未萌发，后续以椭圆叶栎（Quercus ellipsoidalis, QR）种子替代补植。 实验区域外围搭建了地下防囊鼠围栏（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）。整个生长季对样地进行灌溉，避免水分成为限制性资源。研究人员定期测定植被冠层上下的光照强度；定期采集土壤样品以测定铵态氮、硝态氮含量，并采集地下生物量样品；定期刈割地上生物量样品，经过分拣后称重。