Managing the Goldilocks Nutrient: Phosphorus

Phosphorus (P) is generally considered most second-most limiting nutrient to primary productivity, and in some agricultural systems on weathered soils can be as growth-limiting as nitrogen. In only the last 70 years, our species has quadrupled P fluxes in the biosphere by tapping into geological deposits of P to enrich soils under agricultural crop production. While this has been wildly successful in terms of crop productivity, it has encumbered impairment of water resources, from local to continental scales.

Circularizing the P cycle: agricultural re-use of recovered P. Agricultural re-use of P recovered from waste streams stands to mitigate point-source P losses, meet agricultural P needs, and – depending on the speciation of rP– mitigate P losses from agriculture. However, rP speciation differs markedly based on waste stream composition and recovery method, which can further interact with soil and crop characteristics of agricultural sinks. Solubility of rP presents key tensions between engineered P recovery and agronomic re-use because it defines both the ability to separate organic and inorganic P from aqueous streams and the crop-availability of rP added to soil. With the support of the Illinois Nutrient Research and Education Council (NREC), in collaboration with Illinois producers via on-farm trials, and with engagement of the Illinois Farm Bureau, our group evaluates rP production from diverse nutrient-rich waste sources and its re-use in the Midwestern agricultural sink.

Biogeochemical P cycling in intensified agricultural landscapes: pedon to watershed scale. To navigate the trade-offs between agronomic production and environmental quality, we take a hydrobiogeochemical approach to P in the highly intensified landscapes of the US Midwest. From pedon to watershed spatial scales and from week to centennial timescales, we integrated hydrology, agronomy, and soil chemistry to better understand how P is stored and cycled across soil-water interfaces in the agriculturally dominated landscapes of Illinois.

Example of legacy P derived from agronomic P balances at the long-term Morrow Plots experiment, established in 1876. From Rothman et al., in prep.

Managing P limitations in weathered soils in the developing tropics. Soils that achieved the end-state of the Walker-Syers model have evolved multiple co-constraints to soil P availability. In collaboration with the International Center for Tropical Agriculture (CIAT), we evaluate strategies for smallholder (Kenyan highlands) and industrial (Colombian llanos) producers to manage P limitations in such soils.

P-deficient maize in western Kenya
(Rhodic Kandiudox)