Nutrient losses in agricultural production are a global problem. A lysimeter test now shows that soil organisms can make a major contribution to increasing nutrient use efficiency in arable farming and reducing nutrient losses.
When nitrogen fertilisers are not fully taken up by crops, nitrogen compounds enter water bodies or are emitted to the atmosphere in gaseous form. But this need not happen, and the soil biota hold the key. Soil is home to a large part of the world’s biodiversity. Microorganisms dwelling in the soil – collectively referred to as the soil biota – perform a range of soil nutrient conversion processes. Thus, they are major drivers of plant nutrient supply, and nutrient cycles in general. Little was known until now about how different soil biota communities affect the nutrient use efficiency of plant-soil systems.
Agroscope conducted a lysimeter test to investigate the influence of two different soil biota communities of varying complexity on maize nutrition and soil nitrogen losses.
Enriching soil life
In the Agroscope study, eight lysimeter cylinders were inoculated with microorganisms less than 4 mm (4000 µm) in size, comprising diverse bacteria and fungal communities, as well as mycorrhizal fungi. For comparison, a further eight cylinders were inoculated with microorganisms less than 11 µm in size to generate a, in comparison, species-poorer biota community. This contained strongly simplified bacteria and fungal communities. A drainage hole in the bottom of each lysimeter allowed water percolating through the soil to be collected to quantify nutrient leaching losses. Gaseous losses in the form of climate-damaging nitrous oxide (N2O) and gaseous nitrogen (N2) were recorded at the soil surface using sample chambers.
Species-poor soil life reduces nutrient supply and yields
In soils containing a strongly simplified biota (lower biodiversity, predominantly microorganisms), yields were 13% lower, nitrogen uptake 20% lower and phosphorus uptake 58% lower compared with soils containing a richer biota community (higher biodiversity, presence of mycorrhizal fungi).
Species-poor communities enhance nutrient losses
The simplified soil biota was found to increase nitrogen leaching by 65% and gaseous emissions of nitrous oxide (N2O) by 124% and of N2 by 97%. Soil-biological genes for enzymes which could explain the effects on plant growth, nutrition and nutrient losses were identified using metagenomic analyses of the soil DNA.
- The results show that biota communities play a key role in nutrient cycling and have significant potential to increase nutrient use efficiency in arable farming and reduce nitrogen losses to the environment.
- A decline in biodiversity or the loss of certain groups of organisms, e.g. through land-use intensification, could disrupt nutrient cycles – leading to a decline in agricultural productivity while at the same time exacerbating water pollution and climate change.
- Adaptations to agricultural practices aimed at conserving and increasing soil life are needed to stabilise yields, cut fertiliser use and protect the environment.