Multiple application of oxalic acid at low rates for promoting phosphorus input-reduced celery production
Aiming at overcoming the shortcomings of single low-dose or high-dose application of oxalic acid in improving soil phosphorus(P)bioavailability during vegetable growth period,a method involving multiple application of oxalic acid through irriga-tion at low rates was adopted to safely enhance soil P bioavailability for promoting P input-reduced greenhouse vegetable production.The effects of multiple low-dose application of oxalic acid on activating soil P and promoting celery production were evaluated by indoor shallow soil(1 cm thick)incubation experiment and greenhouse pot soil(17 cm thick)experiments with and without celery using two greenhouse vegetable soils with available P values respectively as 88.6 and 46.1 mg·kg-1(named as soil A and soil B,respectively).The soil incubation experiment revealed that multiple application of oxalic acid(0.36 g·kg-1 applied 5 times at 10-day intervals)steadily increases the content of dissolved inorganic P(DIP)in either soil.The potted soil experiment without plants revealed that the effect of elevating DIP level in soil A by such multiple low-dose application of oxalic acid concentrated in 0-10 cm soil layer,especially in 0-5 cm soil layer.The results from the potted celery experiment on multiple application of low-rate oxalic acid(0.18 or 0.36 g·kg-1 for 4 times at 10-day intervals 30 days after celery transplanting)showed that,under the condition of reducing P application by 70%in soil A and 54%in soil B,the application of oxalic acid at either rate increases the DIP content in 0-5 cm soil layer of either soil at celery harvest with the increase being significant at either rate in soil A(by 92.0%and 165%)and at the higher-rate in soil B(64.5%),while the lower-rate oxalic application is more effective in promoting celery growth,especially in soil B,significantly increasing celery yield by 20.0%-33.6%(P<0.05).More studies are needed on the performance and risk of multiple low-rate application of oxalic acid in other soil-vegetable systems.