Effect of sodium chloride on soil characteristics, yield and quality of coconut grown in a laterite soil
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Date
1987
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Department of Soil Science and Agricultural Chemistry, College of Horticulture
Abstract
The coconut palms of the sodium chloride trial conducted at the Regional Agricultural Research Station (K. A. U.), Pilicode, Kasaragod district, Kerala were made use of for the present study. At the Reegional Agricultural Research Station, Pilicode there are two field experiments laid out in 1976, in order to evaluate the effect of NaCl on coconut palms. The soil type of the experiment site is laterite. The design, layout and treatments were the same for both the experiments. It is randomized block design with six treatments and four replications retaining six palms per plot.
Treatments
T1 control
T2 1000 g K2O/palm/year
T3 750 g K2O + 250 g Na2O/palm/year
T4 500 g K2O + 500 g Na2O/palm/year
T5 250 g K2O + 750 g Na2O/palm/year
T6 1000 g Na2O/palm/year
Potassium was applied as KCI and sodium as NaCI. In both experiments the crop is rainfed and the area receives an average annual rainfall of 3200 mm. The present study was conducted with soil and leaf samples drawn from these two experimental sites. The first experiment was conducted with 24 year old stock of hybrid palms (TxD) which received N, P and K as per the recommended dose till 1976 after which the above treatments were superimposed. Thus the palms received the treatments only for the last 10 years from 1976 to till the time of sampling for this study (January, 1986). The second experiment was laid out with newly planted coconut seedlings (DxT) and therefore the treatments were given from planting to till the date of sampling.
The soil, leaf and nut samples were collected from the first experiment for chemical analysis to find out the effect of NaCI on soil characteristics, nutrient uptake, yield and quality of copra. In the second experiment, as the palm had not reached the bearing stage only the soil and leaf samples were collected. Data on the yield and morphological characteristics of the palms were collected from the R. A. R. S., Pilicode. In the second experiment as the palms have not reached stabilized yield, the yield data were not collected. The nutrient contents of leaf and copra were analysed and the quality of oil was estimated. The soil samples were subjected to physical and chemical analysis.
The fertilizer treatments did not differ significantly in respect of the number of functioning leaves retained by the palms in the experiment No.1. Yield was significantly correlated with the number of functioning leaves and a unit increase in number of leaf would correspond to an increase in yield of 5.045 nuts per palm. In the second experiment, the number of functioning leaves was significantly influenced by the fertilizer treatments. The maximum number of leaves (18.48) was recorded by treatment No.4 (50% substitution of K2O by Na2O) and the minimum number of leaves (15.3) was registered by T1 (control).
The treatments did not differ significantly in their influence on the total number of leaves produced per palm per year in the case of the first experiment and on the total number of leaves produced so far by the palms of the second experiment. Differences between treatments were not significant with regard to the number of female flowers produced per palm in the first experiment or the early flowering nature of the palms of the second experiment.
Observations on yield, in the first experiment revealed that yield of the palms increased continuously with progressing period of time and the maximum increase in yield was in T4 (50% substitution of K2O by Na2O). Though there was 104.15 per cent increase in yield in T4 as compared to T1, the difference was not found statistically significant, the significance being lost by marginal difference. When the data were subjected to the analysis of covariance the adjusted treatment mean values varied significantly, the maximum being recorded by T2 (1000 g K2O) and the minimum by T1 (control). Treatment T2 was closely followed by T4 and the difference between T2, T4, T5, T6 and T3 were not significant.
The treatments did not differ significantly in their influence on the copra weight per nut. The percentage oil recovery of copra did not differ significantly by the application of treatments.
Nitrogen and phosphorus uptake by the palms in both the experiments did not differ significantly by the application of treatments. The potassium uptake was decisively influenced by the treatments in both experiments. Treatments receiving higher levels of K showed a correspondingly higher uptake of this element. The treatment T1 (control) registered a higher uptake of K than T6 (1000 g Na2O). The sodium uptake by the palms in both the experiments was also significantly influenced by the treatments. In general palms receiving higher levels of Na retained higher amount of Na in their leaves. Antagonism between K and Na in leaves was also exhibited in both experiments. The uptake of divalent cations (Ca and Mg) by the palms was not decisively influenced by the application of treatments in both experiments. The treatments did not differ significantly in the uptake of CI by the palms in the case of the first experiment. But in the second experiment, the CI uptake of the palms was decisively influenced by the treatments. The treatment T1 (control) which received no application of CI recorded the minimum value which was significantly lower than all other treatment mean values. All other treatment mean values were statistically on par.
The soluble K content of coconut water did not differ significantly by the application of treatments whereas the soluble Na content of coconut water showed significant variation between treatments. The maximum amount of Na was in T6 (1000 g Na2O).
The copra analysis showed that the treatments did not differ significantly with regard to their influence on the extent of N, P and K in copra. The sodium content of copra was found to be influenced by the treatments. The Na content increased with increasing application of Na. The differences between treatments in the case of Ca, Mg and CI contents of copra were not statistically significant.
The analysis on the quality of oil revealed that there was no significant difference in the specific gravity, Refractive index, iodine number and saponification value of oil, between treatments.
The pH and Ec of the soil did not differ between the treatments in both the experiments. The soil physical constants viz., apparent density, absolute specific gravity, percentage pore space, percentage volume expansion and maximum water holding capacity were not significantly different under various treatments in both the experiments. The moisture retension characteristics like field capacity and wilting coefficient and the percentage available water of the soil were not significantly influenced by the substitution of KCI, by NaCI to various extent.
The aggregate analysis of the soil of both the experiment sites showed that there was no significant defference between treatments in the percentage aggregate stebility of the soil. Thus the structure of the soil was not found affected due to the application of NaCI at the rate employed in the experiment.
The treatments did not differ in their influence on the percentage organic carbon in soil, total N in soil and available P in soil in both the experiments.
Available K in soil registered significant difference between treatments in both the experiments. Invariably, treatment receiving the highest amount of K (T2 1000 g K2O) retained the highest amount of this element in soil. In general soil receiving a higher quantity of NaCI recorded higher values for available Na in soil. However, the differences between treatment means were not sufficient to establish statistical significance, in the case of the first experiment. In the second experiment the treatments had significant influence on available Na in soil and the treatment T6 (1000 g of Na2O) registered a significantly higher value of available Na than all other treatments. The available chlorine in soil did not differ significantly due to the application of treatments.
The treatments did not differ significantly as far as CEC of the soil in both experiments was considered. Exchangeable Ca and Mg contents in soil in both the experiments did not differ significantly between treatments. The treatments could decisively influence the exchangeable K in soil in the first experiment but failed to do so in the second experiment. The values of exchangeable K registered by individual treatments increased in accordance with the increasing order of application of K to soil in the first experiment. Exchangeable Na as well as exchangeable Na percentage in soil were not significantly different when the treatment means were compared.
These results showed that substitution of K2O applied to coconut palms as KCI, by Na2O applied as NaCI to the extent of 50 per cent is possible without a reduction in the yield, quality of soil and adverse effects on soil characteristics, under the climatic and soil conditions comparable to that tried in this experiment
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