Solar radiation interception and canopy expansion of sweet corn in response to phosphorus

Insufficient phosphorus (P) availability decreases the yield of Zea mays, particularly for sweet corn crops grown in cool environments. This research examined the mechanisms of yield reductions with initial emphasis on canopy expansion processes that affect the interception of solar radiation. Experiments in two consecutive seasons (2001/2002 and 2002/2003) were grown at a low P site (Olsen P = 6 μg ml⁻¹) at Lincoln, New Zealand. Each experiment contained five rates of P application. In 2001/2002 rates of 0, 50, 100, 150, or 200 kg P ha⁻¹ were applied. In 2002/2003 an additional 0, 0, 10, 20 or 40 kg P ha⁻¹ was applied to the same plots producing total P treatments of 0, 50, 110, 170 or 240 kg P ha⁻¹ summed over the two seasons.When P availability was limited (0 or 50 kg P ha⁻¹) the rates of leaf tip and fully expanded leaf appearance were slower in both seasons. Phyllochrons (°Cd leaf tip⁻¹) were 5 °Cd longer in crops that received 0 kg P ha⁻¹ than those fertilised with ≥100 kg P ha⁻¹. The area of individual leaves was also reduced by low P inputs but the ranking of leaf area by main stem leaf position was conservative. The leaf area of the largest leaf of the unfertilised crops was at least 22% less than the maximum measured leaf area in both seasons. In contrast, P fertiliser application had no effect on leaf senescence.The rate of leaf appearance per plant, individual leaf area and plant population were integrated to calculate green leaf area index (GLAI) and to estimate accumulated radiation interception (RI_cum) for these crops. The total RI_cum throughout the season in the unfertilised crops was 12–28% less than for those crops that received ≥100 kg P ha⁻¹ in both seasons. This difference partly explained the differences in crop biomass production in response to P availability. A sensitivity analysis showed that RI_cum was equally sensitive to changes of the rate of leaf appearance and the area of individual leaves in response to P supply. Both processes need to be incorporated in mechanistic models of P effects on Z. mays which can be used to design efficient P fertiliser strategies.