Effect of Labile Inorganic Phosphate Status and Organic Carbon Additions on the Microbial Uptake of Phosphorus in Soils

Abstract

. Can. J. Soil Sci. 61: 373-385. The effect of labile inorganic phosphate (Pi) status of the soil on the decomposition of added cellulose and on the immobilization, mineralization, and redistribution of.native and addcd P in soils was studiecl in a grcenhousc incubation experiment. Cellulose was addcd at 765 pg C.gr soil with and without P (9 pg'g' soil) every 30 days under adequatc N, H2O, and constant tempreature to two soils of different available P status.Lacli of P eventually slowed down decomposition of added C, but this effect was partially compensated for by increased mineralization of organic P (P.) fbrms. Added P was re<listributed to both Pi 68-697o) andP,,(42-3lTc) forms;higher amounts of P,' were found in the soil with the highest Pi status. The correlation between microbial P uptake and solution P valucs was significant, and microbial C:P ratios ranged from l2: I under high available P conditions to 45:l where P was in low supply' Les effets de la situation des phosphates inorganiques labiles (Pi) du sol sur la d6compo-sition de la cellulosc incorpor6e, et sur I'immobilisation, la min6ralisation et la redistribution du P origincl et ajout6 ont 6td 6tudi6s en sere nous incubation. Des (Canada Soil Survey Committee 1978), were used in this experiment. These soils were air-dried at room temperature, ground to pass a 2-mm sieve, and thoroughly mixed prior to use. The available P status of the Bradwcll soil (rcsin-extractable P-49.1 pg.g r. NaHCOj-cxrractable p-18.0 pg ' g ') was much higher than that of the Oxbow soil (resin extractable P-4.4 pg.gI, NaHCO3-extractable P-3.0 pg . g r). In the first trcatment, cellulose (43% C) was addcd at a rate cquivalent to 765 pg C . g Ieucry 3udays. ln a second treatmcnt cellulose was added at the same rate, and P as KHTPO4 was added at a rate equivalcnt to 9 pg' g I soil. Inthe thirdtreatmenrthesamequantity of P was added without the addition of C, and in the fourth treatment the original soil was incubated wrthout addition of either C or P. Measurements of microbial biomass, CO, evolution. NaHCO:-extractable P' and Po-extractable P, P-. solution P, and resin-extractable P were taken at the time of the maximum decomoosition rate of the added organic materials. as dctcrmined by CO2 production, and at a later stage when the CO2 production had levelled off and approximately reached steady state conditions. At the end of the 9-mo incubation period, the total soil P was fractionatcd rnto various P1 and P6 forms. Experimental details have been described previously (Chauhan et al. 1979).

Biomassa microbiana do solo em sistema de integração lavoura-pecuária em plantio direto, submetido a intensidades de pastejo

“…Para Gijsman et al (1997), a relação C/ P é influenciada pela utilização de leguminosas no sistema. Entretanto, no presente estudo, o que parece ter mais influenciado essa relação foi o C-BM e o alto teor de P disponível no solo (Souza, 2008), tal como indicado por Chauhan et al (1981). 554 kg ha -1 de C e de 30 a 35 kg ha -1 de N para as áreas P-10 e P-20, respectivamente.…”

Long-term effects of fertilizers and manure application on the forms and availability of soil phosphorus

“…The amounts of NaHCO.-P, and NaHCOT-P' varied from 18 to 61 and from 28 to 35 mg P kg-r, respectively, depending on treatment, and both represented an average 9Vo ofPt. These labile pools (resin-and NaHCOT-P1) corresponded to the P form sorbed on the soil surface and to the easily mineralizable organic P (Chauhan et al 1981 For personal use only. ha-l), organic P pools were maintained and the soil P, was significantly increased in manured treatments.…”

Extraction of organic phosphorus in Andosols by various methods

“…Especially, the amount of Ca-P 0' which seems to be the main form of Po extracted by all the methods, was almost nil in all the tested soils. These observations may be ascribed to the fact that a part of the P added by fertilization to the Andosols was supplied as labile PI (increase of Ca-P i amount), but most of it was fixed immediately with the active-AI and -Fe fraction (increase of AI-, Fe-Pi amounts), and the fixed PI may be removed from the P-cycle (Chauhan et al 1981). It is possible that immobilization of the labile PI (PI to Po) occurred by incorporation into the biomass P pool.…”