Phosphorus in Agriculture: A Review of Results from 175 Years of Research at Rothamsted, UK.

Insight into the role of phosphorus (P) in soil fertility and crop nutrition at Rothamsted, UK, and its involvement in associated environmental issues, has come from long-term field experiments initially started by J. B. Lawes in 1843 and continued by others, together with experiments on different soils. Results from the 1940s confirmed that residues of P applied in fertilizers and manures build up reserves of P in soil. There is a strong relationship between crop yield and plant-available P (Olsen P), and a critical level of Olsen P can be determined. For soils near the critical level, P-use efficiency is high when the P applied and offtake by the crop is nearly equal. Soil inorganic P is associated with various soil components and is held there with a range of bonding energies so that when no P is applied, the decline in Olsen P follows a smooth curve. We conceptualize inorganic soil P as being in four pools of vastly varying size, availability for uptake, and extractability by reagents used in routine soil analysis, and with reversible transfer of P between pools. For very disparate soils at Rothamsted and in the United States, there is a strong relationship between the change in Olsen P and P removal/input ratios, suggesting an underlying similarity in inorganic P behavior. Maintaining soil near the critical level should optimize yield and the use of the global P resource while minimizing the risk of transfer of large amounts of P to the aquatic environment.