Combination of short carbon chain dicarboxylic acids with diammonium phosphate increases the diffusion distance and availability of phosphorous in soil
[Objectives]We studied the effects of dicarboxylic acids on increasing the diffusion distance and availability of diammonium phosphate(DAP)in soil,to find an alternative way to increase the efficiency of phosphate fertilizer products.[Methods]Oxalic acid(OA),succinic acid(BA),adipic acid(AA),and suberic acid(SA)were selected as test dicarboxylic acids.The dicarboxylic acids were respectively mixed with DAP powder at a mass ratio of 0.5%,and then granulated to make fertilizer samples(denoted as OAP,BAP,AAP,SAP),ordinary diammonium phosphate(DAP)sample was crushed and granulated in the same way.An incubation experiment was conducted using the five fertilizer samples as treatments and a no fertilizer as control(CK),and each treatment had 18 replicates,i.e.18 petri dishes.At the 1,3,7,14,and 28th days of incubation,a filter paper,previously soaked in FeO solution,was laid on the surface of soil in a petri dish,the fertilizer phosphorus was stained and then scanned for measurement of diffusion distance of fertilizer phosphorus.The soils were sampled at the same time for the determination of available P,Ca2-P and Ca8-P content,pH,and alkaline phosphatase activity.[Results]Compared with DAP,all the DAP-dicarboxylic acid treatments(OAP,BAP,AAP and SAP)increased the P diffusion distance.The diffusion distances of P in the treatments were in order of OAP>BAP>AAP>SAP,that in OAP treatment was 29.5%higher than in DAP.All the DAP-dicarboxylic acid treatments increased soil average available P,Ca2-P and Ca8-P contents to some extent,the increment relative to DAP were 0.48%-12.6%,4.06%-37.1%and 1.25%-20.9%at the 28 days of incubation.Compared with DAP,DAP-dicarboxylic acids enhanced soil alkaline phosphatase activity and decreased pH during 3-28 days of incubation,the highest activity and lowest pH were always recorded in OAP treatment.[Conclusions]Addition of dicarboxylic acids effectively enhanced the availability of phosphorous in diammonium phosphate,due to the longer diffusion distance and higher available P content in soil.Among the tested dicarboxylic acids,addition of oxalic acid is the most effective as the resulted lowest soil pH.
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