Influence of Sewage Sludge Compost on the Cultivation of Maize (Zea mays L.)

Keywords: Municipal solid waste compost, nutrients, Heavy metals, soil physico-chemical properties

Introduction

India’s population has expanded from 342 million in 1947 to 1.12 Billion at present. The urban population is expected to grow to 470 million by 2015. With the growing population, urbanization and demand for consumer goods, both quantity and quality of urban solid waste has changed significantly causing serious environmental problems Urban solid waste is a major contributor to global warming; it leads to surface and ground water pollution through run-off from dump sites and unhygienic sanitary surroundings The environmental management, pollution abatement and control activities require essential build up of systematic knowledge in multidisciplinary areas through research and development.

Sewage sludge, also known as biosolids, is a by product of sewage treatment processes. Land application of sewage sludge is one of the important disposal alternatives. Characteristics of sewage sludge depend upon the quality of sewage and type of treatment processes followed. Being rich in organic and inorganic plant nutrients, sewage sludge may substitute for fertilizer, but availability of potential toxic metals often restricts its uses. Sludge amendment to the soil modifies its physico-chemical and biological properties. Crop yield in adequately sludge-amended soil is generally more than that of well-fertilized controls. Bioavailability of metals increases in sludge amended soil at excessive rates of application for many years.

Plants differ in their abilities to absorb sludge-derived metals from the soil. Composting sewage sludge offers several advantages such as - Microbial decomposition oxidizes the organic material to a fairly stable state resistant to odour production, heat produced during decomposition destroys many of the human pathogens, The compost is a valuable product when used as a soil conditioner and a source of macro and micronutrients favourable to plant growth, Unlike sludge, the compost can be stored conveniently. Soil has been a source of wealth for humans for thousand of years and it continues at present. As a consequence of this prolonged exploitation, significant tracts of soil have become barren land nowadays. Both mineral and organic amendments have been applied to soil in an attempt to slow down this progressive impoverishment, and compost is one of the most effective amendments The addition of compost to the soil improves not only physico-chemical properties like aeration, cation exchange capacity, buffer capacity or porosity, but biotic factors too. From a biological point of view, compost can positively affect microbial populations and their enzymatic activities and stimulates the development of plants by means of the presence of growth factors or the increase of antagonistic activity against phytopathogens, among other factors.

Moreover, biological activity, mainly microbial activity, plays a key role in soil stability and fertility on account of its participation in structuring processes as well as in biogeochemichal cycles. It is basically a special form of waste stabilization that requires special conditions of moisture and aeration to produce stable compost that can be used as a low-grade manure and soil condition. The present study was undertaken to evaluate the enriched municipal solid waste compost on rice growth, Plant Nutrients (NPK) uptake and yield. The aim of this work is : (i) study the effect of application of different rates of sewage sludge compost on the yield and quality of Maize (Zea mays L.) and (ii) assess the short term potential environmental impact on the soil.

Experimental

A field experiment was conducted at the agricultural land in Haradnahalli of Mysore district during June – November 2008. The soil texture of the experimental field is Silty loam with 17 % clay, pH 6.9 and Humus 2. 0 %. The experimental field was irrigated with water from a bore-well. The experiment was laid out in a randomized complete block design with three replications. Net plot size was 3.0 x 5.0 m. The treatments were included in the experiments are given in Table-1. Hybrid maize seeds treated with Derosal at the rate of 2.5 g/kg were sown during the last week of June 2008 in 60 cm apart rows with a single row hand drill using seed rate of 30 kg ha-1. Plant to plant distance of 30 cm. was maintained by thinning at four leave stage. Basudin was applied @ 20 kg ha-1 before first irrigation to control insects specially the maize borer (Chillo partellus Swin). Six irrigations were applied during the whole season according to the requirement of the crop. Hoeing was done manually to control weeds. All other agronomic and plant protection practices were kept normal for all the treatments. Crop was harvested in second week of September 2008. Data on yield and yield components were recorded using standard procedures and analysed statistically.

The compost used was a sewage sludge obtained from Vidyaranyapuram decentralised effluent treatment plant, Mysore . The sludge was mixed with Saw dust and lime. The mixture was composted for 30 days at 75°C to kill pathogenic microorganisms and decomposephytotoxic substances, and then sieved (<20-mm mesh) to remove large bark pieces and stored in swathes. The swathes were turned (mixed) several times in the next 6 months to promote organic matter humification. The final compost met Indian standards for pathogenic microorganisms, organic trace elements, and heavy metals The experimental site was divided into 5 plots (five treatments repeated three times) of 3.0 x 5.0 m .The plots were separated from each other and from the field edge by a buffer zone of at least 1.5 m. The sewage sludge compost was spreadby hand at the end of June 2008^1-4. The trial design was arranged in a completely randomized design of the seven treatments given in Table 1.

Soil samples were taken at depths 0-30 and 30-60 cm were taken from 15 sites (3 samples from each site ) before and after harvest. using a 5 cm-diameter bucket auger. The samples were homogenised, air-dried, ground and sieved through a 2 mm mesh before analysis. The determination of the main physico-chemical characteristics were carried out according to official analytical methods³. The soil available trace elements concentration was determined after digesting the samples with aqua regia. Grain yield per treatment was determined. The yield of dry grain was calculated in kg ha^-1. Corn ears were also randomly collected for each treatment, washed with distilled water and oven-dried at 65°C to constant weight and powdered and subjected for further analysis of heavy metals. The average compositions of the compost applied are summarised in Table- 2. It was observed that the bio waste has high organic matter content and acceptable amounts of N and P and total heavy metals and hence it is an useful organic-mineral soil amendment.

Results and discussion

The trial design arrangement of various proportions of SSC and mineral fertilizer is given in Table-1. Table-2 reveals the important physical and chemical characteristics of soil before harvesting in three depths. The characteristics of sewage sludge compost are presented in the Table-3. The values in the table infer that all the micronutrients and macronutrients are within the acceptable limit of agriculture^5,6. As significant differences were not found among plots the data correspond to average values of the 15 plots as shown in Figures 1 and 2. The plants need some macronutrients (phosphates, nitrates) that are not always present in the correct form in the soil. Bacteria play a fundamental role in biochemical cycles, permitting the recycling of the organic compounds and make them useful for the superior organisms.

Figure-1 · Concentration of NH4-N and NO3-N in Soil after harvest of Maize crop with nitrogen fertilizer and various treatment sewage sludge compost

Figure-2 · Concentration of Nitrogen in maize grains with nitrogen fertilizer and various treatment sewage sludge compost

Table-5 shows the mean values obtained for, N-NH₄ and N-NO₃, respectively. The N-NH₄ contents were maximum in all the treated plots than in the unamended-soil. Values obtained for treatments T₃ and T₄ were significantly lower than for other treatments in the first 30 cm of soil. The mean values of N-NO₃ (Table 6) showed an increase with in treatments T₄ and T₅ were significantly different than in other treatments applied and also in the unamended soil, in the first 30 cm of soil. In the 30-60 cm soil depth there was a remarkable increase in this parameter, significant in T4 compared to the other treatments. In general, this increase was also showed at depths of 40-60 cm and 60-80 cm.

Grain yield of rice was significantly influenced by different treatments (Table-6). Among the treatments T₃ and T₄ recorded higher grain yield (9500 & 9800 kg ha^-1) than other treatments. This was followed by T₁ and T₂ with value of 8800 and 9000 kg /ha respectively. As compared to the application of T₀ which recorded Lowest grain yield (7200 kg/ha). High rate of mineralization of nitrogen from sewage sludge applications must have encouraged excessive vegetative growth of maize⁷. The contents of nitrogen in grains was maximum in treatment T₀ (11.9 mg kg^-1) and increased significantly with increasing sewage sludge compost, reached 10.8,11.2,11.6,11.8 mg kg^-1 at the highest application rate. The contents of P and K decreased from T₀ to T₄ (4.67 to 2.2kg ha^-1). This might have caused due to low rate of phosphorus mineralization from the applied sewage sludge. Increased rates of sewage sludge application in the experimental soil enhanced the uptake of calcium and magnesium by corn. The concentration of Ca, Mg, Zn, Cu, Pb, Ni, Cr and Cd (figure-3) in the grains increased significantly with increasing sewage sludge compost level and were observed high at all the treatments compare to T₀, but the values are below permissible limit except for the treatment T₃ and T₄ which recorded the highest values. The values of Cr and Cd contents were below detectable level in all the treatments. There were no visual signs of toxicity or deficiency due to treatments in any part of the crop, which is further evidence that plant growth was not negatively affected by the sewage sludge compost treatments, except for the increase in heavy metal concentration in treatments T₃ and T₄.

Figure-3 · Levels of nutrients in Maize grains with nitrogen fertilizer and various treatment sewage sludge compost

Conclusion

The nitrogen concentrations of soil in the top layer was highest among all the different treatments and decreased in the bottom layer. The yield and quality of corn grain (macro and micronutrients) in the compost treatments exceeded when compared to mineral fertilizer treatment (control). It can therefore be concluded that, with the exception of T₃ and T₄ treatment (compost by high-rate application), all the other treatments are appropriate for the corn crop with Silty loam soil. The use of compost in appropriate rates provides a good quality and quantity corn yield for short term, without producing any appreciable environmental damage⁸. However, further studies should be done to evaluate the possible changes in Silty loamsoil available trace elements in the medium and long term.

References

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