Effects of phosphorus fertilizers on spatial-temporal distribution of soil available phosphorus, cotton yield and phosphorus use efficiency

Objective We compared the distribution of commonly used water-soluble P fertilizers in soils within a fertigation cycle (7 days), and the soil available P content at different cotton growth stages, aiming to provide a reference for the rational application of P fertilizer in drip irrigation cotton fields.

Methods Field experiments were conducted in 2020 and 2021. Four treatments were set up, including: no P fertilizer (P0), and applying mono-ammonium phosphate (MAP), phosphoric acid (AP) and ammonium polyphosphate (APP). The horizontal and vertical distribution of P fertilizers was determined every day within a fertigation cycle (7 days). At the squaring, initial flowering, full flowering and boll opening stage, 0−60 cm soil samples were collected for determination of available P, and plant samples were collected for measurement of dry matter weight, total P content and yield.

Results Within a fertigation cycle, all the three applied P fertilizers were mainly distributed in the 0−5 cm away and 0−15 cm below the emitters. AP treatment was recorded the highest soil available P in the first 3 days, while APP treatment was recorded that during the 5−7 days of fertigation. All the three P fertilizer treatments significantly increased available P in 0−40 cm soil. AP treatment had higher soil available P than MAP and APP treatment at the bud stage, and APP treatment had higher available P at flowering to boll opening stage of cotton. P treatments significantly increased the total dry matter weight of cotton, APP treatment exhibited the highest dry matter at boll opening stage, which was 7.5%−7.8% and 7.8%−8.1% higher than MAP and AP treatment, respectively. APP also showed the best effect on cotton yield, P use efficiency, P recovery efficiency and agronomic efficiency, its cotton yield was 3.2%−7.7% and 5.6%−6.0% higher than MAP and AP, P use efficiency was 10.9%−18.4% higher than MAP, P recovery efficiency was 43.2%−60.3% and 12.0%−37.5% higher, and agronomic efficiency was 12.9%−47.4% and 24.2%−34.4% higher than MAP and AP treatment, respectively.

Conclusions MAP and AP are more effective in increasing soil available P at squaring stage, while APP is more effective at the middle and late growth stages of cotton, so APP is more effective than MAP and AP to promote the growth of cotton reproductive organs and nutrient uptake, and thus improve the yield and P use efficiency.