Bioavailability of Phosphorus and Micronutrients in the Soil-Plant-Microbe Continuum

An increasing need to produce food for the expanding world population creates significant pressure on suitable land already in production and requires continuous expansion of food-producing ecosystems into less fertile areas. In every such food-producing system, crops and pastures must be provided with sufficient nutrients for vigorous growth and high outputs, putting an emphasis on understanding soil-plant microbe interactions governing nutrient acquisition by plants. This review will summarise the available knowledge on relevant interactions underlying plant acquisition of P and micronutrients (with an emphasis on Mn). Soils resulting in P and micronutrient deficiency in crops and pastures are abundant in the world, but such nutrient deficiency arises from poor P and micronutrient mobility rather than low total amounts present in soil (Rengel, 2001). Hence, the plant-available nutrient fraction and the concentration in the soil solution may be insufficient to satisfy plant requirements (Jorquera et al., 2008; Rengel and Marschner, 2005). Around 90% of the total P use in the world today is for food production (Jasinski, 2006). Hence, modern agricultural systems are dependent on continual inputs of P fertilizers processed from phosphate rock. Yet, the world reserves of phosphate rock are becoming increasingly scarce, and estimates are they will be depleted within 50-100 years, with a global peak in usage of P reserves occurring by 2040 (Jasinski, 2006). While the exact timing might be disputed, it is widely accepted that the quality of P rock is decreasing and cost increasing (indeed, the price of phosphate rock has risen 7-fold in the 14 months since Feb 2007) (Cordell, 2008).