Effects of Combining Minjingu Phosphate Rock and Triple Superphosphate with Selected Plant Biomass on Phosphorus Availability in Two Soils with Contrasting Properties

Abstract

An incubation experiment was conducted to assess the influence of combining Minjingu phosphate rock (MPR) with Gliricidia (GLC) sepillm leaves and maize stover (MS) 011 MPR dissolution and availability of the dissolved P in Magadll and Kilosa soils. The two soils have been classified as Oxic Haplustult and U1tic Haplustalf, respectively. Treatments tested were: an absolute control (ABS), and addition of either MPR, MPR+GLC, MPR+GLC+MS, TSP, TSP+GLC, GLC, GLC+ MS. The rate of application of MPR and TSP was 40 mg Pkg^-1 while the rate of biomass application was I g^-1. All samples were incllbated for 42 days but sub-samples were withdrawn from each treatment periodically for determination of NaOH- and Bray I -P. In addition, a P adsorption study was conducted to determine the P adsortion parameters of the two soils. The results indicated that at 42 days of incubation 75% of the applied MPR had dissolved in Magadu soil while 50% of the MPR had dissolved in Kilosa soil. Addition of plant biomass did not improve the dissolution of MPR in both soils. The amollnt of MPR dissolved in Magadll soil was comparable to thatreleased by TSP. However in Kilosa soil, Oil average the amount of P dissolved from MPR was much If?ss by 54% than that from TSP. On the other hand, Bray I - P from the MPR treatmellts was comparable in Magadu and Kilosa soils despite the large differellce in the extent of MPR dissollltion in the two soils. Addition of organic materials caused slight increases in Bray I-P il1 both TSP and MPR treatmellts in the two soils. The level of Bray I -P Fom the TSP treatmellts was on average 50% higher in Kilosa soil than in Magadu soil. This was attributed to higher P fixation in Magadu soil than in Kilosa soil. It was concluded that soil factors especially pH and P adsorption capacity had big influences on MPR dissolution and availability of the released P. However co-application of MPR and organic materials did not enhance dissolution of MPR bllt tended to increase available P.

Keywords: Gliricidia sepium. maize stover, NaOH-P, Bray-l-P, PR dissolution, P fixation

Tanzania J. Agric. Sc. (2007) Vol. 8 No. 1,67 -78