Nutrient enrichment influences grassland ecosystem structure, typically manifested by reduced species richness and increased productivity. Quantifying the long-term impacts of nutrient enrichment on grasslands contributes to understanding eutrophication effects on grassland, particularly for grasslands adapted to low soil nutrient status. Overextended time periods, nutrient enrichment may modify soil fertility. The Ukulinga Grassland Nutrient Experiment situated on a natural C4 grassland was set up in 1951 on the Ukulinga research farm, South Africa. Continuously applied treatments on plots measuring 2.7 × 9 m include combinations of nitrogen at 0, 7, 14 and 21 g m⁻² per annum, phosphorus at 0 and 2.8 g m⁻² per annum and lime at 0 and 225 g m⁻² applied every five years. Nitrogen sources included ammonium sulphate (acidifying) and limestone ammonium nitrate (less acidifying). Grass species composition was influenced by both nitrogen forms. In contrast, forb species composition was more sensitive to LAN. We found evidence of nitrogen limitation on aboveground net-primary production. However, species richness (for grass and forbs) declined with increasing ammonium sulphate levels, owing to increased soil acidity and high aluminium concentrations. Aluminium toxicity can affect overall species composition by replacing Al-sensitive species with Al-tolerant species on site.

养分富集影响草原生态系统结构，通常表现为物种丰富度降低和生产力提高。量化养分富集对草地的长期影响有助于了解富营养化对草地的影响，特别是对于适应低土壤养分状况的草地。时间过长，养分富集可能会改变土壤肥力。位于天然 C4 草原上的乌库林加草原养分实验于 1951 年在南非乌库林加研究农场建立。在 2.7 × 9 m 的地块上连续施用的处理包括每年0、7、14 和 21 gm ^{-2的氮、每年 0 和 2.8 gm -2}的磷以及 0 和 225 gm ^{-2的石灰的组合}每五年申请一次。氮源包括硫酸铵（酸化）和石灰石硝酸铵（酸化程度较低）。草种组成受两种氮形态的影响。相比之下，福布物种组成对 LAN 更敏感。我们发现了地上净初级生产氮受到限制的证据。然而，由于土壤酸度增加和铝浓度高，物种丰富度（草和禾本科植物）随着硫酸铵水平的增加而下降。铝毒性可通过在现场用耐铝物种替换对铝敏感的物种来影响总体物种组成。