Phosphorus (P) is critical for maximizing agricultural production and represents an appreciable input cost. Geologic sources of P that are most easily mined are a finite resource, while P transported from agricultural land to surface waters contributes to water quality degradation. Improved knowledge of P timing needs by corn (maize) can help inform management decisions that increase P use efficiency, which is beneficial to productivity, economics, and environmental quality. The objective of this study was to evaluate P application timing on the growth and yield components of corn. Corn was grown in a sand-culture hydroponics system that eliminated confounding plant–soil interactions and allowed for precise control of nutrient availability and timing. All nutrients were applied via drip irrigation and were therefore 100% bioavailable. Eight P timing treatments were tested using “low” (L) and “sufficient” (S) P concentrations. In each of the three growth phases, solution P application levels were changed or maintained, resulting in eight possible combinations, LLL, LLS, LSL, LSS, SLL, SSL, SLS, and SSS, where the first, second, and third letters indicate P solution application levels from planting to V6, V6 to R1, and R1 to R6, respectively. All other nutrients were applied at sufficient levels. Sacrificial samples were harvested at V6, R1, and R6 and evaluated for various yield parameters. Plants that received sufficient P between V6 and R1 produced a significantly higher grain yield than plants that received low P between V6 and R1 regardless of the level of P supply before V6 or after R1. The grain yield of plants that received sufficient P only between V6 and R1 did not differ significantly from plants that received only sufficient P (SSS), due to (1) a greater ear P concentration at R1; (2) an efficient remobilization of assimilates from the stem and leaf to grains between R1 and R6 (source–sink relationship); (3) a higher kernel/grain weight; and (4) less investment into root biomass.

The high demands of corn (Zea mays L.) grain production coupled with water quality goals and phosphorus (P) conservation pose a great challenge to farmers and society and necessitate improved P utilization efficiency (PUtE: grain yield per mass total P (TP) content). The objective of this study was to evaluate PUtE among six Pioneer corn hybrids released over a span of 75 years. Corn was grown in a sand culture hydroponics system that eliminated confounding plant–soil interactions and root architecture and allowed for precise control of nutrient availability. Four P concentration levels (4, 7, 10, and 12 mg P L⁻¹) were applied to hybrids released in 1936, 1942, 1946, 1952, 2008, and 2011. Nutrients other than P were applied at sufficient levels. Shoots and roots were harvested at maturity (R6) and biomass and P concentration determined. Results showed that total biomass did not differ among hybrids, but partitioning of biomass varied with hybrid. Grain yield varied between hybrids, but there was no trend with the year of release. Grain P content was negatively correlated with stem P content (R² = 0.89). PUtE differed between the most recently released hybrids (2008 and 2011) whereas older hybrids had intermediate and similar PUtE. Grain yield was not solely determined by TP in the plant, but was strongly influenced by biomass and P partitioning, which was manifested as relative differences in PUtE between hybrids. While the PUtE did not necessarily change as a function of the breeding period, there were differences between hybrids. The findings highlight the critical role of the source–sink relationship in determining PUtE and grain yield.

Phosphorus (P) influx kinetics of plants, characterized by Imax (maximum uptake rate) and Km (P concentration where the uptake rate equals half of Imax), s