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Responses of biomass, chlorophyll and macro- and micronutrient uptake of rice (Oryza sativa L.) to organic and chemical fertilisers

Mohammad Ali Bahmanyar1, Hemmatollah Piradshti2

1Associate Professor, Department of Soil Science, Email: mabahmaniar@yahoo.com
2Assistant of professor, Department of Agronomy and Plant Breeding
Sari Agricultural Sciences and Natural Resources University, Sari, Iran

Abstract

The effect of different amounts of organic fertilisers (compost, vermicompost and sewage sludge) and chemical fertilisers on biomass, chlorophyll content and micronutrient uptake in rice (Oryza sativa L.) seeds, was investigated at the research farm of Sari Agricultural Sciences and Natural Resources University in 2007. Treatments consisted of 20 and 40 t/ha compost, vermicompost and sewage sludge without chemical fertiliser and with 50% of the chemical fertiliser needed by plants according to soil testing, chemical fertiliser treatment (100 kg K2SO4, 150 kg super phosphate and 150 kg urea per hectare) and control (without organic or chemical fertiliser). The results indicated that chlorophyll content at tillering and heading stages and K content of rice plants did not differ significantly among treatments, although the plants grown in 40 t/ha compost enriched with 50% chemical fertiliser had more chlorophyll content at around 30 and 60 days after transplanting compared to the control. All composts, except 20 t/ha sewage sludge, either alone or enriched with chemical fertilisers, produced more biomass than the control. In terms of nutrient accumulation, 20 t/ha compost alone or enriched, 40 t/ha compost enriched, 20 t/ha sewage sludge enriched and 40 t/ha sewage sludge alone or enriched resulted in higher amounts of N in rice seeds.

Keywords

micronutrient, organic fertiliser, biomass, rice

Introduction

Rice is a major staple food crop grown in Asia. Large amounts of organic wastes, such as biosolids, animal manures and household wastes are produced in Iran. It is well known that management practices with organic materials influence agricultural sustainability by improving physical, chemical and biological properties of soils. To increase the productivity and to meet the heavy demand for food of the growing population, it is necessary to recycle available resources and wastes. Wastes of animal and plant origin are one of the major under-utilised resources in many countries (Jeyabal and Kuppuswamy 2001) and these organic wastes could easily be used in agriculture. For example, vermicomposting has been recognized as an eco-friendly technology for converting organic wastes into high value organic manure. By definition, composting under controlled conditions, involving earthworms, is called vermicomposting (Pramanik et al. 2007).Vermicompost contains most nutrients in plant-available forms such as nitrates, phosphates, and exchangeable calcium and soluble potassium (Orozco et al. 1996; Arancon et al. 2004). Sewage sludge is a concentrated source of nutrients with a potentially high agricultural value. Improvements in soil chemical properties that have been reported following the use of organic by-products include; increased crop yield (Maynard 1993 ; Arancon et al. 2004; Courtney and Mullen 2008) and increased plant available N, K, Ca and Mg. Since much of leaf nitrogen is involved in enzymes associated with chlorophyll, the chlorophyll content evaluation using SPAD and its relation with leaf nitrogen concentration could provide an indirect assessment of leaf nitrogen status (Chapman and Barreto 1997).The current study was implemented to assess the effects of land application of different organic fertilisers on biomass, chlorophyll content and uptake of some macro- and micronutrients by rice (Oryza sativa L.) and to compare the response to a commercial mineral fertiliser treatment.

Methods

The experiment was performed on a rice crop (O. sativa L., variety Tarom Mahali, at 16 plants per m2) at the Research Farm at Sari Agricultural Sciences and Natural Resources University, Sari, Iran from May to September 2007. The experiment was laid out as a randomized block with three replications. The soil was a silty clay and the treatments applied were: compost (C), vermicompost (VC) and sewage sludge (SS) (Table 1) at 20 and 40 t/ha alone or enriched by 50 % of the chemical fertiliser needed as determined by soil analysis, a complete chemical fertiliser (CF) (100 kg K2SO4, 150 kg super phosphate and 150 kg urea per ha.) and one treatment which was not amended and represented the control soil. The size of each plot was 12 m2 with 0.5 m between plots to prevent interference between treatments. The crop was sown at the end of April. The field was flooded one day after transplanting and the water depth was maintained at 5-10 cm until 10 days before maturity. Plants were harvested at physiological maturity, at the beginning of October. Chlorophyll content of leaves was estimated by a Minolta 502 SPAD meter when plants were at tillering, flowering and heading stages. Mature rice heads were harvested within a randomly placed 400 cm2 quadrat and dried at 60°C for 24 h to give dry weight biomass. Grain was separated and weighed (shoots + grains). After harvest, plant materials from each plot were allowed to dry. Total N in plant materials was determined according to the modified Kjeldahl method. Total elemental (K, Fe and Zn) analysis in plant materials was carried out after dry-ashing at 450°C and digestion of the ash in 6 M HNO3. Fe and Zn were determined by atomic absorption spectrophotometry. The experimental data were subjected to analysis of variance (ANOVA) using SAS (SAS Ins. 1990) tests with mean separation by the Duncan Multiple Range Test using a significance of P < 0.05. Pearson correlation coefficients were used to determine significance of correlations between rice yields and other traits.

Table 1. Properties of the organic fertilisers

Organic Fertilisers

pH

EC
(dS/m)

TOC
(g/kg)

C/N

Fe
(g/kg)

Zn
(g/kg)

C

7.41

10.07

131.8

11.14

7.15

0.76

VC

8.05

2.05

156.6

11.45

5.46

0.05

SS

7.44

18.22

179.8

7.8

16.54

0.47

Results

Chlorophyll content at tillering and heading stages and K content of rice plants did not differ significantly among treatments although the plants grown in 40 t/ha compost enriched with 50 % chemical fertiliser had more chlorophyll in leaves at around 30 and 60 days after transplanting compared to the control (Table 2).

All composts, except 20 t/ha sewage sludge, and chemical fertilisers, produced more biomass than the control. This indicates that the different compost types provided the required plant-available nutrients and improved soil characteristics (MacKey et al. 1989; Marcote et al. 2001). Among fertilisers, 20 t/ha compost alone or enriched, 40 t/ha compost enriched, 20 t/ha sewage sludge enriched and 40 t/ha sewage sludge alone or enriched caused higher N accumulation in rice seeds (Table 2). None of the vermicompost treatments resulted in an increased level of N in rice seeds.

Table 2. Effect of organic fertilisers on chlorophyll content, biomass and N, K, Fe and Zn concentration of seeds in rice.

†Means followed by the same letter within a column are not significantly different using Duncan’s test at the 5% level.
††Significant differences are designated with asterisk/s: (*) at P <0:05 and (**) at P <0:01 and ns (not significant).

Conclusion

The three composts used varied in composition in terms of nutrients and elemental content (Table 1). Accordingly, their effects on studied traits varied depending on parameter and application rate. Overall, application of composts raised levels of micro- and macro-nutrients in seeds and chlorophyll content of leaves to concentrations greater than the control. There was variation between the compost types and application rates in their effect on seed N, Fe and Zn content, and in particular the vermicompost treatments had little effect on seed N. This experiment was only conducted for a single season. Longer-term monitoring is required to determine the long-term effect of the compost types and application rates on plant nutrition and soil characteristics.

References

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Chapman SC and Barreto HJ (1997). Using a chlorophyll meter to estimate specific leaf nitrogen of tropical maize during vegetative growth. Agronomy Journal 89, 557-562.

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