Dlomitic limestone (CaCO3.MgCO3) is recommended for a tea soil which is provides both calcium and magnesium (Tea Circular 1989). Zoysa (2002) reported that the application of dolomite powder to tea soils is an important agronomic practice. This helps the maintenance of sustainability of tea cultivation in Sri Lanka. The amount of dolomite required to be applied to the soil depends on the soil pH and the buffering ability of the soil. Because most soil can resist pH changes to an appreciable extent when large amounts of materials either acid forming or base forming fertilizers added (Zoysa et al., 2008). Dolomite should be applied to pruning field soon before or after the pruning, while ensuring even distribution on the ground. The beneficial effects of liming are: improvement of soil pH suitable for nutrient availability and absorption, supply of an inexpensive source of magnesium and calcium, reduction of possible toxicity by aluminum and manganese and improvement of soil physical and biological conditions. Iron, aluminum, titanium, manganese, silica, sodium, potassium and organic matter are the usual minor constituents of dolomite (Pathirana, 2000).

In this context this study was carried out to develop dolomite recommendation for the mid country wet zone of Sri Lanka with the specific objective of to study effect of application of dolomite on major and micro nutrient availability of tea growing soils.

2 Materials and Methods

A field experiment was conducted in 2015 at Rathode tea estate. The site is situated in the mid country wet zone of Sri Lanka at latitude of 7°31'4.44" N and longitude of 80°43'23.87".The experimental site lies at an altitude of about 884 mean sea level. It is characterized by average rainfall of 1250-3150 mm, soils are derived from the colluvial material , well drained and very deep having dark reddish brown, clay loam surface underlain by dark reddish brown, loam surface soils (Mapa.,1999).

2.2 Treatments and Experimental Design

The field experiment was carried out using the tea cultivar TRI 2023 .The Randomized complete Block Design (RCBD) with 3 replicates was used as an experimental design. Field plots were established for five levels of treatments. Rectangular plots of highest length were recommended because of sloppiness of land. Each plot was separated by the gourd row which separated the treated area in order to prevent the treatment effect in any adjacent plots. Each individual plot was marked with 30 bushes.

2.3 Fertilizer Application

Fertilizer was applied to all plots evenly. Nitrogen, K2O and P2O5 applied at the rate of 320, 120 and 35 Kg/ha/year respectively.

2.4 Sampling Procedure

Soil samples from two depth 0-15cm and 15-30cm were collected from the randomly selected places in each plot as a bulk and sub sample was taken from the bulk. During soil sampling dead plant, stones, area near tree and other inert materials were removed. A part of the sub sample was allowed to air dried and passed through the 2mm sieve prior to chemical analysis in order to get homogeneous sample.

2.5 Soil Analytical methods

Soil sample was analyzed at laboratory of soil and plant nutrition Division, Tea Research Institute, St cooms Estate Talawakella. Trace elements iron and manganese were extracted by DTPA and concentration was determined by AAS. Aluminium extracted by KCl and concentration was measured using spectrophotometer at 530 nm wavelength (Bertsch et al., 1981). Exchangeable Ca2+, Mg2+ and K+ were extracted by ammonium chloride (Blackmore et al, 1987). K determined by using flame photometer. Soil Ca and Mg were determined by using AAS.

2.6 Statistical Analysis

Data were subjected to an analysis of variance (ANOVA) to examine the effect of dolomite limestone application on major and micro nutrient availability of tea soil. A statistical analysis was conducted using Statistical Analysis System (SAS) window version 9.1 and Microsoft Excel 2007 package. The least significance difference (LSD) test was used to separate significantly differing treatment means after main effects were found significant at P < 0.05.

 

Table 1 Treatments

 

3 Result and Discussion

3.1 Effect of application of Dolomite on major Nutrient content of Tea soil

The effect of different rate of dolomite on soil Ca, Mg and K are shown in the Table 2 respectively. Different rate dolomite did not affect significantly on availability of Ca in both depths.

 

Table 2 Effect of application of different rate of dolomite on soil Exchangeable Ca, Mg and K at 0-15cm and 15-30 cm

 

Figure 1 Major nutrient content at 0-150 cm depth

 

Figure 2 Major nutrient content at 15-30 cm depth

 

3.1.1 Exchangeable Calcium

Ca is the major element present in dolomite which mitigating the soil pH. That displaces the H+ and Al ions present in soil exchangeable sites. Also the soil of an experiment area has considerable buffering capacity and the pH also not significant. According to that this results obviously report that Ca2+ neutralized soil acidity and had no effect on available Ca on soil.

 

3.1.2. Exchangeable Magnesium

At 0-15cm depth Mg concentration had significant difference. Application of 4000kg dolomite/ha/pruning cycle had highest Mg concentration compare to dolomite rate of 3000 and plot without dolomite (Control). Plot with 1000, 2000 kg/ha/pruning cycle dolomite had no effect. Dolomite provides Mg itself and Mg also responsible for the arrest the soil pH.  As application of lime had high Mg saturation in soil was found by Athanase et al., (2013). Mg released by applied fertilizer is a may be a reason for high Mg in control plot. Mg content at 15-30cm had no effect. Increasing trend of soil exchangeable Mg was found by Krishnapillai et al (1992) in study with incubation of different rate of dolomite with different soil type. They reported soon after incubation Mg increased in all type of soil with increasing rate of dolomite and there was no change in Mg with time period.

3.1.3 Exchangeable Potassium

There was no change in K content at 0-15cm depth. But considerable change was observed in concentration of K at 15-30cm depth. Highest concentration of K was observed in 1000kg/ha/pruning cycle applied plots. Dolomite rate of 2000, 4000, control plots did not show any significant effect. Lowest K concentration was found in dolomite rate of 3000 kg/ha/pruning cycle.  Kovacevic and Rastija (2010) have shown that liming did not affect potassium availability on acid soil But Matale, soil series showed higher base saturation than the other soils and also CEC of these soil also very high (10-20 cmolc kg-1) (Jayalath et al., 1998). Because of this habit of soil there was no effect on Exchangeable cations in soil. Krishnapillai et al., (1992) reported that the exchangeable K+ had no variation with increasing rates of dolomite application. Similar findings reported by Jensen (1972) and Udo (1978).

3.2.1 Soil Exchangeable Aluminium (Al)

According to results obtained from this study, significant effect on soil exchangeable Al was not observed. But there was a reducing trend was observed when increasing rate of dolomite at 0-15cm depth (Table 3) and there was no considerable change at 15-30cm soil depth.

 

Many soil scientists showed that decreasing pH decreased Exchangeable Al concentration in soil.  Pathirana,(2000) observed significant reduction of Exchangeable Al by application of dolomite in acid tea soil. There are many reports about the beneficial Ca effects on the amelioration of Al-toxicity in different crops growing in acid soils (Mora et al., 1999; Mora et al., 2002). Other studies have shown that soil pH increases after the application of Ca amendments due to the displacement of Al3+ and H+ by Ca2+ from the exchange sites into the solution (Alva and Sumner, 1988; Mora et al., 1999). 

 

Figure 3 Al (mg/kg) deviation at different depth

 

3.3 D.T.P.A Extractable Mn and Fe in soil

 

Table 3 Effect of application of different rate of dolomite on trace elements in soil

 

The experimental data available do not furnish evidence that the application of different date of dolomite on the availability of D.T.P.A extractable Mn at both depths (Table 3), while lowest value was recorded in dolomite rate of 4000 kg/ha/pruning cycle.

 

Figure 4 Fe (mg/kg) deviation at different depth

 

Figure 5 Mn (mg/kg) deviation at different depth

 

Figure 6 Overall available trace nutrients in soil

 

Soil available Fe also did not show significant variation between the treatment in 0-15cm depth but the significant different was observed in 15-30 cm soil depth. Lower Fe concentration was observed in dolomite applied plots than control which had high available Fe in soil.

 

4 CONCLUSION

This study shows the advantage of incorporating dolomite which helps to supply the soil with adequate quantities of available magnesium and at the same time to reduce the concentration of aluminium and to eliminate possible toxic effects of aluminium, manganese and iron in tea soils. Although it was observed that the soil exchangeable K did not show much variation with increasing rates of dolomite application.

 

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