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Water hyacinth is a serious menace in low land ecosystems and it’s spread has
threatened water quality and aquatic life. Various biological, chemical and physical
methods that have been employed to control the weed has yielded minimal results.
Hence management through utilization is a viable strategy. It can be effectively utilized
in many ways to support crop production.
Co-composting has been proved as a promising technique for safe and quick
disposal of the weed by utilizing the co-substrates viz., poultry manure, sawdust,
biochar, glyricidia, paddy straw, dried leaves and cattle manure. As the weed
accumulates N, P, K and other essential nutrients, compost made from water hyacinth
can be utilized for improving soil fertility and crop production. Hence, the present
investigation entitled “Evaluation of water hyacinth co-composts for nutrient retention
in lateritic soil” was under taken in the Department of Soil Science and Agricultural
Chemistry at College of Agriculture, Vellanikkara during 2020-2021. The objectives
were; (i) To find out the suitable combination of water hyacinth and co-substrates for
enhancing the quality of water hyacinth composts (ii) To assess the nutrient retention
capacity of different co-composts in lateritic soil.
Different co-substrates were collected from nearby areas and water hyacinth
was collected from Kole lands of Thrissur. Water hyacinth and co-substrates were
characterized prior to composting. Water hyacinth co-composts (vermi compost) were
prepared using the aforesaid substrates in concrete tanks. The physical and chemical
properties of the composting mixtures were recorded at 40 days interval starting from
20 days of composting until 100 days. The yield of water hyacinth co-composts was
estimated and the various co-composts were characterized for their physical and
chemical properties.
Incubation study was conducted to evaluate the nutrient retention capacity of
different water hyacinth co-composts in lateritic soil during December 2020 with eight
treatments and three replications (soil+ 7 co-composts and soil alone as absolute
control). The lateritic soil for study was collected from Instructional Farm, Vellanikkara
and analysed for chemical properties. Compost amended soils were incubated for a
period of 28 days and nutrient retention capacity (N, P, K, Ca, Mg, S, B, Zn) was
estimated at 4 different time periods after incubation (7, 14, 21, 28 days).
Data on characterization of co-substrates revealed that substrates vary in their
chemical properties and nutrient content. Among the co-substrates, poultry manure
possessed many favourable characteristics. Changes in physical and chemical
properties of composting mixtures at different intervals indicated the progress of
composting process and stage of compost maturity. All the co-substrates gave
reasonably good yield of water hyacinth co-composts. A notable increase in compost
yield to an extent of 159.7 per cent was realized in the biochar treatment. Addition of
co-substrates improved the bulk density and porosity of water hyacinth co-composts.
Application of co-substrates improved the pH of final compost. Highest increase was
noticed in the treatment with paddy straw. Addition of paddy straw had significant
adverse effect on the electrical conductivity of final co-compost (170.6 % increase in
EC over water hyacinth sole treatment) and all the other treatments showed EC below
maximum permissible limit for plant growth.
The total carbon content of all the co-composts was higher than water hyacinth
sole compost. Nitrogen content of the co-compost was improved to a greater extent by
the application of paddy straw and poultry manure. Co-composts with sawdust, biochar
and dried leaves had significantly lower quantity of nitrogen compared to water
hyacinth sole compost. Glyricidia and poultry manure were highly effective in
improving total phosphorus content of the co-compost. Total potassium content of
water hyacinth compost was significantly improved with the addition of co-substrates
like paddy straw and biochar, the extent of increase being 192 and 170 per cent,
respectively. Carbon to nitrogen ratio of water hyacinth co-compost was significantly
lowered by using poultry manure as a co-substrate.
Addition of poultry manure improved all the three secondary nutrients viz., Ca,
Mg and sulphur to a higher magnitude. No favourable effect was noticed on the boron
content of co-compost by the addition of different co-substrates. However, Fe and Mn
levels of final co-composts were considerably lower than the water hyacinth sole
compost. This could be considered as a favourable effect of co-composting of water
hyacinth with different substrates. Zinc content of the co-compost was significantly
improved by the inclusion of co-substrate particularly with the use of poultry manure
and dried leaves. Copper content of the co-compost was significantly higher with the
addition of poultry manure as co-substate.
The addition of co-compost to lateritic soil, improved retention of nutrients
particularly nitrogen. The only exception was co-compost with paddy straw (0.9 per
cent decrease in the nitrogen retention capacity). Irrespective of the treatments, cocompost retained all the phosphorus and boron present in the co-compost amended soil.
The soil’s potassium, magnesium, sulphur and zinc retention capacity could be
improved when amended with water hyacinth co-compost. In general, soil with biochar
co-compost showed significantly high retention capacity with respect to plant nutrients
particularly nitrogen.
Further study should be focused on field experiments to test the agronomic
efficiency of different water hyacinth co-composts, testing suitability of various crop
residues and organic wastes as co-substrates and to derive suitable substrate
combinations and ratios to eliminate the adverse effects of co-substrate on compost
quality.