Phosphate biofertilizers as renewable and safe nutrient suppliers for cropping systems: A review

Abstract

Sustainable agriculture highly depends on soil microorganisms to supply essential nutrients for plants and circulate the nutrient cycles in cropping systems. These microorganisms which are commercially formulated and briefly named "biofertilizers" can significantly reduce fossil fuel consumption, environmental degradation, and production cost related to agriculture. Phosphate biofertilizer is one of the most important groups of these beneficial microorganisms which plays a notable role in nutrient preparation for crops. Although these biofertilizers are usually known as phosphate suppliers for cropping systems, they can also provide other macro- and micronutrients to crops. Fungi and bacteria form two major groups of phosphate biofertilizers which can live freely or as symbiont organisms in agricultural soils. Mycorrhiza is a symbiont fungus which increases plant uptake of phosphate, nitrogen, and micronutrients and improves soil structure via formation of an extensive and dense mycelial network connected to plant roots. In contrast, phosphate solubilizing microorganisms are usually free living and able to solubilize insoluble phosphate compounds in soil mainly via releasing a wide range of organic acids and chelating metabolites. However, the effectiveness of these microorganisms is significantly influenced by edaphic factors and field management practices. For example, tillage as a usual practice in most of the cropping systems has negative effects on the absence and activity of mycorrhizal fungi. Application of chemical fertilizers which is another routine operation in modern agriculture also notably reduces the survival and effectiveness of phosphate biofertilizers. This review article presents the results on the main phosphate biofertilizers which can potentially be applied in sustainable agriculture, their action mechanisms, and important factors influencing their effectiveness.