Abstract: A field experiment was conducted to evaluate the comparative effect of Zn levels applied by different methods i.e. nursery root dipping in 1.0% ZnSO4, 0.20% ZnSO4 solution spray after transplanting and 10 kg Zn ha-1 by field broad cast method. A significant increase in Zn content of rice leaf before and after flowering and a significant decrease in P content of straw and paddy and starch content of paddy was recorded for all the methods. N, K and Zn of paddy and straw and Zn contents of roots increased significantly with the application of zinc irrespective of the methods over control. Soil application of Zn was rated superior because it gave significantly higher content of N in rice paddy.
Introduction
Zinc deficiency is the most common problem in the flooded rice. The deficiency of Zn in rice soils of Pakistan has been observed (Tahir et al., 1979). Zinc deficiency is dramatically manifested by chlorosis, necrosis, early death of seedling or delayed development and reduced crop yields, an explicit information on micronutrient status of rice crop is urgently required. Various investigations have been carried out on the past in this aspect of micronutrient (Tahir et al., 1986). Zn applied at 100 ppm to nursery or 10 ppm after transplanting or 10 kg ha-1 as basal dressing (Yoshida and Tanaka, 1969) proved effective in alleviating its deficiency in rice. Dipping rice seedling roots in 1% ZnO suspension is noticed as the most practical method for curing Zn deficiency in rice (Yoshida et al., 1970). In a field study, ZnSO4, ZnCl2, ZnO and ZnCO3 as effective materials for removing zinc deficiency in rice and 10-100 kg ha-1 Zn application was suggested its optimum rate (Tahir et al., 1979). In a green house and field experiments Zn-enriched nursery beds @ 20 kg Zn ha-1 proved equally effective or superior to conventional ZnSO4 field broad cast method (Rashid et al., 2000). Rice growth was similarly affected with zinc applied as ZnO, ZnSO4 and Zn-EDTA but Zn uptake in plants differed (Giardano and Mortvedt, 1972). Moreover, Zn applied to surface or mixed in soil affected yield and Zn uptake more favorably than that placed below the seed (Giardano and Mortvedt, 1973). Dipping the seedlings in 2% ZnSO4 solution or 25 kg Zn ha-1as basal dressing or spraying 0.5% ZnSO4 solution once or twice to the transplanted crop were proved equally effective (Kumar et al., 1996). Soil application of Zn prior to flooding was more effective than its flood water application for rice (Giardano, 1977). Keeping all these points on view, the study was carried out to know the chemical composition and grain quality of rice and the comparative effect of different methods of zinc fertilizer for managing Zn deficiency in transplanted flooded rice grown in calcareous soil.
Materials and Methods
A field experiment was conducted at the research area of Faculty of Agriculture, Gomal University D.I.Khan. Thirty days old nursery of a rice variety IRRI-6 was transplanted in standing water. The Randomized Complete Block Design (RCBD) was used with three replication and a plot size of 2m x5m. Row to row and plant to plant distance was maintained at 20 cm. Following experimental treatments were applied.
Half of the nitrogen as urea and whole of phosphorous as TSP and potassium as K2SO4 was incorporated before transplanting while remaining N was used at panicle emergence. Physical and chemical characteristics of composite soil samples taken from experimental field were determined, following the methods as described in Methods of Soil Analysis by Page et al. (1982).These measurement are presented in Table 1. Crop was harvested at maturity; grain and straw samples for all the treatment were oven dried at 70°C. Plant material was prepared by dry ash method as described by Issac and Johnson (1975) and Zn was determined by atomic absorption spectrophotometer.
| Table 1: | Physico-chemical characteristics of soil |
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Ground rice straw and paddy samples were analyzed for nitrogen, phosphorous, potassium and zinc following standard procedures as given by Page et al. (1982). Statistical analysis of all the data was done using Fisher Analysis of Variance Technique and least significant difference test was applied at 5% probability level to determine the difference among treatment means (Steel and Torrie, 1984).
Results and Discussion
Zinc content of rice leaf before flowering
The zinc content in rice leaf before flowering, is reported in Table
2 indicated that the highest zinc content of 62.50 ppm was recorded in the
treatment receiving 0.20% ZnSO4 by foliar spray followed by that
receiving 10 kg Zn ha-1 by soil dressing and 1.0% ZnSO4
by root dipping which might be owing to the direct application of zinc to plants
and its absorption by the plant tissue thereby increasing the leaf zinc content.
The lowest zinc content of 19.40 ppm was obtained in control. The results showed
that all the doses of zinc applied by different methods significantly increased
the leaf Zn content over control. Similar results were reported by Kumar et
al. (1997).
Zinc content of rice leaf after flowering
The data for the zinc content of the rice leaf after flowering as affected
by zinc applied by different methods are presented in Table 2.
The highest zinc content of 45.10 ppm was recorded in the plots receiving 0.20%
ZnSO4 by foliar spray followed by that receiving 10 kg Zn ha-1
by soil dressing and 1.0% ZnSO4 by root dipping. Significantly the
lowest zinc content of 19.00 ppm was recorded in the plots where no zinc fertilization
was done. However, the differences amongst the methods of zinc application were
non-significant and the Zn content of rice leaf varied from 44.60 to 45.10 ppm.
Similar results were reported by Kumar et al. (1997).
Zinc content of rice root
The influence of zinc doses applied by different methods on the Zn content
of rice root is shown in Table 2. The zinc doses affected
Zn content in root significantly over control. The highest Zn root content of
78.10 ppm was obtained from the plots receiving 10 kg Zn ha-1 by
soil dressing which was statistically similar to the plots receiving 1.0% ZnSO4
by root dipping but was significantly different from plots receiving 0.20% ZnSO4
by foliar application which showed that soil application of Zn had more beneficial
effect on the availability of soil Zn as compared to other methods. It was probably
attributed to its synergetic effect on the enhancement of root development,
which increased the uptake of the Zn from soil through diffusion from the immediate
vicinity of the plant roots. The lowest Zn content of 37.15 ppm was recorded
in control. Mehdi et al. (1990) also reported that an increase in the
level of zinc applied through soil increased the zinc content of roots.
Carbohydrate content of rice paddy
The data presented in Table 2 manifested that significantly
maximum value of 87.10% starch content was recorded in plots where no zinc fertilization
was done which was at par with the plots receiving 0.20% ZnSO4 by
foliar spray.
| Table 2: | Zn content of leaf, roots and starch content of paddy as influenced by different methods of Zn application. |
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| Table 3: | Nitrogen, Phosphorous, Potassium and Zinc content of rice paddy and straw |
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| Mean values with the same letters are non-significant at p ≤ 0.05 | |
The lowest starch content of 81.30% was recorded in the plots receiving 10kg Zn ha-1 by soil dressing which was statistically at par with that receiving 1.0% ZnSO4 by root dipping or 0.20% by foliar spray. The adverse effect of Zn application on starch content of rice paddy was probably due to either decrease in formation or an increase in utilization of carbohydrates in tissue. Rajub (1999) reported similar results.
Nitrogen content of rice paddy
The data on % N content of rice paddy shown in Table 3
indicated that nitrogen content in paddy under different methods of Zn application
increased significantly over control. Significantly highest value of 0.98% N
was obtained in the plots treated with 10 kg Zn ha-1 by soil dressing
followed by that receiving 1.0% ZnSO4 by root dipping (0.94%) and
0.20% ZnSO4 by foliar spray (0.91%). The lowest N content of 0.76%
was obtained in control. The increase in N content by application of Zn through
broad casting might be ascribed to its beneficial effect on soil microorganism
helpful in nitrogen recycling and its release from organic sources. Obata et
al. (1990) and Yaseen et al. (1999) also reported somewhat similar
results.
Phosphorous content of rice paddy
The data pertaining to P concentration in paddy are presented in Table
3. The results showed that application of zinc by different methods decreased
the P content of paddy over control, which might be due to the antagonistic
effect of Zn on P absorption. Significantly highest P content of 0.27% was recorded
in control followed by the plot receiving 10 kg Zn ha-1 to soil and
that receiving 1.0% ZnSO4 by root dipping. The lowest P content of
0.22% was obtained from the plots receiving 0.20% ZnSO4 by foliar
application. The lowest P content in the paddy treated by foliar application
was attributed to its higher Zn content which might have decreased the P translocation.
Chaudhry et al. (1992) and Yaseen et al. (1999) also reported
similar results.
Potassium content of rice paddy
The data regarding K content in paddy as shown in Table 3
indicated that significantly maximum K content of 0.205% was recorded in plots
treated with 10 kg Zn ha-1 by soil dressing which was statistically
at par with the plots treated with 1.0% ZnSO4 by root dipping but
was significantly higher than that of 0.20% ZnSO4 by foliar spray.
It showed that soil Zinc application method had more beneficial effect on the
availability of soil K as compared to other methods. It might be attributed
to its synergetic effect on the enhancement of root development, which increased
the uptake of K from soil through diffusion and mass flow from the immediate
vicinity of the plant roots. The lowest K content of 0.170% was recorded in
the control. Yaseen et al. (1999) also reported somewhat similar results.
Zinc content of rice paddy
The data shown in Table 3 indicated that zinc application
by different methods increased significantly the paddy Zn content over control.
The highest zinc content of 32.45 ppm was recorded in the plots treated with
0.20% ZnSO4 by foliar spray, which was statistically at par with
the plots treated with 10 kg Zn ha-1 by broad casting but differed
significantly from the treatment of 1.0% ZnSO4 by root dipping. It
might be attributed to its direct absorption in plant tissue resulting in increased
grain content of zinc. Similar results were also reported by Devarajan and Ramanathan
(1995) and Srivastava et al. (1999) who reported that zinc application
to zinc deficient soil increased the total biomass, grain yield, zinc concentration
in the grain and uptake of zinc by the straw and the grain.
Nitrogen content of rice straw
The data for the N content as affected by zinc levels is reported in Table
3. The results showed that the effect of Zn on the N content was significant.
The highest value of 0.53% N in rice straw was recorded in the plots treated
with 10 kg Zn ha-1 by soil dressing followed by that receiving 1.0%
ZnSO4 by root dipping and by that receiving 0.20% ZnSO4
by foliar spray. The increase in N content of rice straw suggested that zinc
application by soil dressing might be effective in the proliferation of roots,
which increased the uptake of nutrient from the soil and ultimately supplied
to the aerial parts of the plant. The lowest N content of 0.38% was noted in
the plots where no zinc fertilization was done. Singh et al. (1990) and
Yaseen et al. (1999) reported similar results.
Phosphorous content of rice straw
The data for P content as influenced by Zn, applied by different methods
is shown in Table 3. The results showed that all the doses
of zinc applied by different methods decreased the P content significantly over
control, which indicated the antagonistic effect of Zn on P absorption. Significantly
the maximum mean P content of 0.048% was recorded in control followed by the
plots receiving 10 kg Zn ha-1 by soil dressing and that receiving
1.0% ZnSO4 by root dipping. The lowest P content of 0.028% was obtained
for the plots receiving 0.20% ZnSO4 by foliar spray which might be
attributed to the higher Zn content in straw which might have inversely decreased
the P translocation. As regards methods used to apply zinc, all were statistically
similar. These results are in conformity with those of Chaudhry et al.
(1992) and Yaseen et al. (1999).
Potassium content of rice straw
The data for K content as affected by Zn levels applied by different methods
are reported in Table 3.The results showed that application
of zinc by any method increased significantly the K content in straw over control.
The maximum K straw content of 1.913% was obtained in plots treated with 10
kg Zn ha-1 by soil dressing which was followed by the plots treated
with 1.0% ZnSO4 by root dipping and that treated with 0.20% ZnSO4
by foliar spray. It showed that soil application of Zn had more beneficial effect
on the availability of soil K as than other methods. It was attributed to its
synergetic effect on root proliferation, which increased the uptake of the K
element from soil through diffusion and mass flow from the immediate vicinity
of the plant roots. The lowest K content of 1.250% was observed in control,
showing thereby the response of K to zinc application and the ability of zinc
to enhance the availability of soil K. These results are in accordance with
those reported by Yaseen et al. (1999).
Zinc content of rice straw
The data on zinc content of rice straw as influenced by different doses
of zinc applied by different methods are presented in Table 3.
Zinc application by various methods increased the Zn content of rice straw significantly
over control but the differences among them were nonsignificant and the Zn content
on an average varied from 27.37 to 30.12% against significantly the minimum
of 22.10% in control. Srivastava et al. (1999) and Yaseen et al.
(1999) reported similar results.