Effects of different basal-top dressing ratios of polyphosphate fertilizers on the growth of potted cotton under drip irrigation in calcareous soil

Objectives The effects of three kinds of polyphosphate fertilizer on the growth and phosphorus utilization efficiency of drip-irrigated cotton in calcareous soil was investigated in a pot experiment to expand the pool of knowledge on efficient nutrient management in cotton production.

Methods Ammonium phosphate with degrees of polymerization of 2.3, 1.8 and potassium tripolyphosphate with degree of polymerization of 3.0 were individually mixed with conventional diammonium phosphate, respectively to obtain three kinds of mixed polyphosphate fertilizers, and expressed as APP1, APP2, KTPP. 3% of the P₂O₅ in mixed phosphate fertilizer was provided by polyphosphate fertilizers. The amount of P application was P₂O₅ 0.2 g/kg, each mixed polyphosphate fertilizer was applied as three basal-top dressing ratios of 7∶3 (F_7∶3), 1∶1 (F_1∶1) and 3∶7 (F_3∶7), and the control without phosphate fertilizer (CK). The plants of cotton were harvested at 110 days after emergence, and the dry weight and total phosphorus contents of shoot and root parts of cotton were measured. The soil available phosphorus contents at 0–8 cm and 8–16 cm depth were measured respectively.

Results The soil available P of F_7∶3 treatment was significantly lower than those of F_1∶1 and F_3∶7 at 0–8 cm depth but at 8–16 cm, the soil available P obtained from F_7∶3, F_1∶1, and F_3∶7 treatments were similar. Under F_7∶3, the soil available P content of KTPP treatment was significantly higher than APP1 and APP2 treatment at 0–8 cm depth, whereas it was higher under KTPP and APP1 than APP2 when treated with F_1∶1 and F_3∶7 at both soil depths. The shoot dry weight and root dry weight of cotton treated with F_1∶1 were significantly higher than those from F_7∶3 and F_3∶7. The boll number of cotton in F_1∶1 was the highest and that in F_3∶7 was the lowest. Under F_1∶1 treatment, numbers of cotton boll from KTPP and APP1 were significantly higher than that of APP2. The shoot P uptake and P utilization efficiency of F_7∶3 and F_1∶1 were significantly higher than that of F_3∶7. Under F_1∶1 and F_7∶3 of phosphate basal-topdressing treatments, the shoot phosphorus uptake and phosphorus utilization efficiency of cotton were KTPP>APP1>APP2.

Conclusions In calcareous soils, the best effect of polyphosphate fertilizer on cotton was obtained from KTPP, followed by APP1 then APP2. Among the three kinds of polyphosphate fertilizers, the application of basal-top dressing ratio at 1∶1 had the best effect on cotton biomass accumulation and P utilization efficiency.