Effects of hyacinth residues on chemical properties and productivity of degraded tropical soils

Water hyacinth (Eichhornia crassipes) is an aquatic weed that has blocked many navigable water-ways in the tropics. Attempts have been made to control or erradicate it to no avail. Its capacity to produce large biomass in a short time could be explored to seek other ways of utilizing it as a biofertiliser. An evaluation of the potential of water hyacinth (WH) residue as a biofertiliser was carried out in the green­house using a split-plot in a Radomized Complete Block Design (RCBD) experiment with three replica­tions of each treatment. Top soil samples taken from an Entisol, Lithic Usorthent, (S1) and an Ultisol, Typic Paleustult, (S2) constituted the main plot treatments, whereas the sub-plot treatments were control (C), inorganic fertilizer (N-P-K-Mg at the rates of 240, 60, 240 and 80 kg/ha) (F), 20 t/ha water hya­cinth (WH1), WH1 + F, 40 t/ha water hyacinth (WH2), WH2 + F, WH1 + 20 t /ha rice mill waste (WH1 + RW1), WH1 + 20 t/ha poultry droppings (WH1 + PD1) and WH1 + 10 t/ha RW and 10 t/ha PD (WH1 + RW1 +PD1). All amendments were mixed with the soils and incubated for 10 days before planting. The F treatment was applied at maize planting. Data were collected on maize performance and changes in soil chemical properties.Results showed that exchangeable cations, CEC, OC, total N, avail­able P and pH increased in the WH-amended soils relative to the controls in both S1 and S2. The more fertile S1 benefited from these amendments more than S2 and showed that maize performance during the first cropping was better on S1 than S2, whereas during the residual cropping the crop performed equally well on both soils. Lower maize dry matter yields occurred in the residual than the first crop­ping. Also the less fertile S2 had higher residual effect of the residues than S1. Generally, WH mixed with either PD or RW or both performed better than when used alone. These results indicate that WH has a lot of potential for use as a biofertilizer on these low-fertile, fragile, tropical soils, especially if mixed with PD or PD+RW. Key words: Soil chemical properties; Soil fertility improvement; Maize performance; Water hyacinth residues; Poultry manure; Rice mill wastes; Nigeria. Agro-Science Vol.2(2) 2001: 44-5