Because each of the species has a different nutrient and it is the precisely the diversity of it which makes the soil more efficient.

Dr Patricia Fortuny thank you for your contribution to the discussion

Healthy ecosystems contain a diversity of species, and each species plays a role in ecosystem function; therefore, species diversity as well as ecosystem diversity is essential to maintaining ecosystem services. For example, many medications are derived from natural chemicals made by a diverse group of organisms. It is often measured because high biodiversity is perceived a synonymous with ecosystem health. In general diverse communities are believed to have increased stability, increased productivity, and resistance to invasion and other disturbances. Biodiversity can be measured at many different levels including genetic, species, community, and ecosystem. One way to measure biodiversity is to assess species richness of an ecosystem, which is the total number of distinct species within a local community. Knowing what species inhabit an ecosystem, and how many of each kind there are, is critical to understanding that ecosystem's structure and function, and predicting future changes. Scientists who look at the variation of life in a forest, a stream or a patch of soil are looking at its biodiversity.Ecosystems with higher species diversity tend to be more resilient. If an ecosystem has a diverse community of organisms, they are not all likely to be affected by a disturbance in the same way. Species diversity tends to increase with habitat heterogeneity. Communities that have increased habitat variation have an increased number of ways to divide up the available niches. The number or variation of available niches varies by organism-type. Increasing species diversity can influence ecosystem functions such as productivity by increasing the likelihood that species will use complementary resources and can also increase the likelihood that a particularly productive or efficient species is present in the community. Biodiversity is essential for the processes that support all life on Earth, including humans. Without a wide range of animals, plants and microorganisms, we cannot have the healthy ecosystems that we rely on to provide us with the air we breathe and the food we eat. And people also value nature of it.