Abstract:
Phospho-composts of different mix ratios (5:5, 7:3, 8:2 and 9:1) were produced
through thermophilic co-composting of poultry manure (PM) and sewage sludge
(SS) with ground phosphate rock (GPR). Composted PM and SS without GPR
addition were included as control. Cured phospho-composts were chemically
characterised and used for both laboratory incubation and greenhouse studies,
respectively for phosphorus (P) mineralisation and bioavailability, over a period of
42 days. Results revealed that Bray-P1 concentration measured in compost
amended soils at 14, 21 and 42 DAI differed significantly (P<0.05) and ranged
between 5.47 and 11.14 mg kg-1 and between 5.28 and 11.78 mg kg-1 in poultry
manure and sewage sludge-based phospho-composts, respectively. The maximum
amount of cumulative P mineralised of 16.06 and 9.98 mg kg -1, respectively in PM
and SS-based phospho-composts were obtained from the 8:2 mix ratio. The
content of the acid detergent fibre of the different phospho-composts showed
positive and significant correlation with cellulose, lignin and total organic carbon
(TOC). Similarly, cellulose as well as C:P ratio showed significant correlation with
both lignin and TOC. The polynomial relationship between cumulative P mineralised
and the various GRP and manure mix ratios revealed significant and positive R2-
values of 0.731 and 0.613 for PM and SS-based phospho-composts, respectively.
The maximum amount of maize tissue P uptake of 0.12 and 0.11 mg pot-1 in PM and
SS-based phospho-compost respectively were also obtained from the 8:2 mix ratio
while the least amount of 0.04 mg P pot-1 was obtained from GPR and unamended
pots. Maize tissue P uptake following the phospho-compost application was
significantly affected by the differences in soil type. Tissue P uptake was 0.06 and
0.11 mg P/pot, respectively in low potential and high potential soils with a
significantly higher value. The use of the different phospho-composts showed great
potential for amelioration of P-deficiency problems in crops while thermophilic cocomposting
improved the solubility and bioavailability of P from non-reactive GPR.
Keywords: Ground phosphate rock; poultry manure; sewage sludge; phosphocomposts;
phosphorus mineralisation; soil fertility management.
