Soil P forms and P uptake P under intensive plant growth in the greenhouse

Randy  Killorn; Carlos  Henríquez

Soil P forms and P uptake P under intensive plant growth in the greenhouse

Autores

Randy Killorn

Carlos Henríquez

Editor

Universidad de Costa Rica

Descripción

The concentration of available soil (P) isa function of the equilibrium established amongdifferent soil P forms through numerous anddifferent reactions in soil. The objective of thisstudy was to examine the changes in P forms andP supply under exhaustive extraction conditionsin soils from 3 different land use areas. In order toestablish a greenhouse experiment, representativesoil samples (0-20 cm) were taken from threefields located adjacent to one another, in a TypicHapludands in Costa Rica. One field was acoffee plantation (Coffea arabica var Catuai),the second a sugar cane plantation (Saccharumspp. var 611721), and the third a secondaryforest. Sorghum (Sorghum bicolor var Glazer41) was planted in 1-liter pots and harvested4 times consecutively. Treatments were no Pand P application (100 mg kg-1) for each of thedifferent land-use soil samples. Shoot and rootdry matter and total P uptake were determined.Soil samples were taken before and after each ofthe 4 plant growth cycles and analyzed using amodified Hedley et al. (1982) soil P fractionationmethodology. Labile-Pi, NaOH-Pi, HCl-Pi,extractable-Po, and residual-P were determined.Applied P increased labile-Pi, NaOH-Pi andHCl-Pi. Statistical changes were not observedin extractable organic P and residual-P due to Papplication. The NaOH-Pi and HCl-Pi seemed to act as a temporary pool of applied P. The possibleparticipation of residual-P in replenishment oflabile-P and NaOH-Pi was observed. The amountof plant P uptake was closely related to the initialamount of labile-Pi and was higher in coffeethan in forest and sugar cane soils. The labile-Pwas depleted by plant uptake. Rapid changes inreversibly available soil P forms (NaOH-Pi andHCl-Pi) were observed during the experiment.Our results suggest the occurrence of very rapidand dynamic changes between available andunavailable soil P forms in response to fertilizerapplication and plant uptake, supporting the ideaof a continuum among the P forms.