World Phosphorus Use Efficiency in Cereal Crops

Agronomy Journa l • Volume 109, I s sue 4 • 2017 Phosphorus is the second most limiting nutrient in crop production aft er N. Batjes (1997) estimated that P defi ciencies can be found in nearly 67% of world land designated for crop production. Hinsinger (2001) reported that crop production is reduced due to P defi ciency on an estimated 5.7 billion hectares of land. Due to the non-renewable nature of P resources, appropriate management should be considered to lengthen the life-span of phosphate reserves. According to Roberts and Stewart (2002), P reserves will last 343 yr at current mine production rates. Heff er et al. (2006) concluded that based on current consumption, P reserves are suffi cient for approximately 100 yr. Similarly, Smil (2000) projected that P reserves will be depleted in the next 50 to 100 yr. Th e International Fertilizer Development Center (IFDC, 2010) estimated that global P reserves range between 300 and 400 yr. Van Vuuren et al. (2010) stated that depletion of phosphate rock is not imminent. Recently, Van Kauwenbergh et al. (2013) estimated that the world has over 300 yr of P reserves (phosphate rock) and 1400 yr of resources. However, Edixhoven et al. (2014) expressed concerns about recent updates due to indistinct defi nitions for reserves and resources. Edixhoven et al. (2014) was challenged and criticized by Scholz and Wellmer (2016) stating that biased interpretations had been drawn. However, considering fi nite, non-renewable and the non-substitutable nature of P, increasing PUE remains important. Phosphorus is abundant in soil; however, the concentration of plant available P in the soil solution is generally low (Clarkson and Grignon, 1991). Th ese values were 0.1 to 10 μM as reported by Hinsinger, (2001). Marschner (1986) stated that P concentration in soil solution and P-buff er capacity are among the most relevant factors responsible for the availability of P to plants. Soil pH infl uences chemical properties and biological processes, including solubility, mobility, and availability of nutrients and trace metals. According to Lindsay et al. (1989), in alkaline soils, P can precipitate with Ca forming insoluble hydroxyapatite, octacalcium phosphate, and dicalcium phosphate. In acidic soils, P can precipitate as minerals of Fe, and Al (strengite and variscite, Sato et al., 2005). Both of these minerals decrease the availability of P for plant growth (Lindsay et al., 1989). Clay fractions such as amorphous hydrated oxides of Fe and Al, in addition to gibbsite, goethite, World Phosphorus Use Effi ciency in Cereal Crops