Objectives Long-term shallow rotary tillage by small power mechanical engineering often leads to shallow top soil layer and thick plough pan in the root layer, so subsoiling has been used to break the plough pan and promote root distribution into deep soil. This research studied the phosphorus (P) placement depths for high P uptake and P fertilizer use efficiency of maize in high-yielding spring maize under subsoiling measurement.

Methods In 2014, a split field experiment was conducted in Tongliao City, Inner Mongolia. Rotary tillage and subsoiling plus rotary tillage were set up as the main plots, and P placement depths of 6 cm (P6), 12 cm (P12), 18 cm (P18), 24 cm (P24) were set up as sub-plots, using no P fertilization as control (CK). In 2015, field experiment was conducted under the subsoiling tillage to investigate dry matter, P content, P uptake of maize and analyze the differences of P uptake and use efficiency of maize among P placement depths. The effects of matching relationship between P distribution in soil profile and root distribution on P uptake and utilization of P fertilizer were also discussed.

Results The grain yields of spring maize under different P placement depths showed P12 > P6 > P18 > P24, grain yields were higher under subsoiling plus rotary tillage than rotary tillage, and the maize yield under treatment P12 was significantly higher than other treatments under subsoiling plus rotary tillage. Plant P content in P12 treatment was the highest, followed by that in P6 at silking and ripening stage. The P12 treatment had the highest dry matter yield of maize which was higher in subsoiling plus rotary tillage than rotary tillage. There was no significant difference in dry matter yield among P application depths at silking and maturity stage under rotary tillage, and no significant difference among various P application depths at silking stage under the subsoiling plus rotary tillage practice, while P12 treatment had significant higher dry matter yield than P24 treatment at maturity stage. P12 treatment had the highest P uptake, 7.47% higher than P6 treatment (2014) before silking and 3.85% higher (2014) after silking under rotary tillage practice. P uptake in P12 treatment was 10.32% (2014), 9.01% (2015) higher before silking and 9.34% (2014), 10.20% (2015) higher after silking than P6 treatment under subsoiling plus rotary tillage practice. Subsoiling promoted the phosphorus uptake of maize, more obvious after silking. P uptake efficiency and P fertilizer use efficiency were the highest in P12 treatment, followed by P6 treatment and the lowest in P24 treatment. The P uptake in P12 treatment was significantly higher than other treatments. P fertilizer use efficiency in P12 treatment was 19.22% (2014) higher under rotary tillage practice, 29.22% (2014) and 29.04% (2015) higher under subsoiling plus rotary tillage practice than P6 treatment.

Conclusions Moderate deep application (12 cm) of P fertilizer under the subsoiling tillage was found to be capable of improving P uptake and P fertilizer use efficiency, and increasing grain yield in the studied area, and should be taken as an effective way to reduce P fertilizer rate and increase P use efficiency in high-yielding spring maize.