Deep phosphorus fertilizer placement increases maize productivity by improving root-shoot coordination and photosynthetic performance

It’s well known that the development and distribution of roots could be regulated to obtain deep soil resource and enhance the grain yield by increasing the depth of fertilization, but little is known about whether increasing P fertilization depth can optimize the root distribution to delay leaf senescence, enhance photosynthetic performance and root-shoot coordination or not. We conducted a field experiment that tested the following four placement depths of P fertilization: 5 cm (P5), 10 cm (P10), 15 cm (P15), and 20 cm (P20). The experiment was designed to explore the regulatory effects of the P fertilization depth on the root growth and distribution, the photosynthetic performance, the root-shoot coordination, the yield formation, the N and P fertilizer utilization of maize plants. We found that deep P placement did indeed alter the root parameters. In the 20–60 cm soil layer, both the root dry weight and length of P15 treatment were on average 23.2% higher than those of P5 treatment. The specific root length and specific root surface area of P15 treatment were 4.5% and 5.6% higher than those of P5 treatment. In addition, the P15 treatment achieved a significantly improved photosynthetic performance over the P5 treatment: The leaf area index at the R6 stage was 10.2% higher, the leaf senescence index from the R2 to the R6 stages was 31.4% lower, the photosynthetic rate at the R3 stage was 25.9% higher. The P placement depth also optimized the root-shoot coordination: The ratios of root weight to shoot weight, root surface area to leaf area, and root length to leaf area of P15 treatment were 6.7%, 13.8%, and 12.7% higher than those of P5 treatment, respectively. Finally, the root P and N uptake efficiency, the photosynthetic P-use efficiency, and the physiological P-use efficiency of P15 treatment were all significantly higher than those of P5 treatments. And together these responses had the effect of increasing the mature biomass by 12.5%, and the grain yield by 22.0%. In conclusion, increasing the P fertilization placement depth to 15 cm regulates the growth and development of the root system, which in turn improves the capability of plant to uptake and utilize N and P in the soil, delays the onset of leaf senescence, enhances its photosynthetic performance and biomass accumulation rate, and thus ultimately increases the yield.