The Effect Of Tithonia Diversifolia (Hemsley) A. Gray Biomass On The Solubility Of Rock Phosphates: A Laboratory Incubation Experiment. Tropical And Subtropical Agro Ecosystems.

Abstract

A 16-week laboratory incubation experiment was conducted to evaluate the effect of Tithonia diversifolia leaves on the dissolution of Minjingu (MPR) and Busumbu (BRP) rock phosphates in a Kenyan Oxisol. Triple superphosphate (TSP) fertilizer was included as a positive control. Soil samples were extracted with anion exchange resin (AER) and mixed anion-cation exchange resin (ACER) after 1, 7, 14, 28, 56 and 112 days to estimate plant available P. Soil P fractionation was carried out using solutions of 0.5M NaHCO3, 0.1M NaOH and 1M HC l. The highest mean AER-extractable P concentrations for BRP and MPR treatments were 6.0 and 20 mg kg-1 respectively; while that of the TSP treatments was 24 mg kg-1. The AER-extractable P concentrations were in the order TSP >MRP > BRP. The ACER-extractable P concentrations were higher than those of AER. Application of tithonia at 10 tons ha-1 in combination with MPR caused a significant (P<0.05) depression in AER-extractable P. The TSP treatments had the highest NaHCO3-Pi and NaOH-Pi (labile and moderately labile inorganic P) fractions which ranged from 22 to 32% and 45 to 59% of total added P, respectively; followed by MPR treatment which had NaHCO3-Pi and NaOH-Pi fractions ranging from 13 to 22% and 26 to 34% of the total added P, respectively. Addition of tithonia decreased the NaHCO3-Pi and NaOH-Pi fractions from the MPR treatments by 2 to 8%. The RP treatments had the highest HCl-Pi (undissolved RP) fraction.