Effect of different fertilizers on the growth of coconut seedlings, availability of some nutrients and soil microbial activities

S.R.M.R. Attanayake1, C.M. Nanayakkara2 and N.A. Tennakoon3
1Agriculture Biotechnology Centre, University of Peradeniya, Sri Lanka
2Department of Plant Sciences, University of Colombo, Sri Lanka
3Soils and Plant Nutrient Division, Coconut Research Institute, Lunuwila, Sri Lanka

The present fertilizer application is manly based on chemical fertilizers which are costly and exerts negative impacts on soil health. Therefore a study was planned to find out the effect of different fertilizers on the growth of coconut seedlings, availability of some nutrients and soil microbial activities with the aim of developing a fertilizer mixture that supports the plant growth with simultaneous improvement of soil health.

Eight months old coconut seedlings of CRIC 65 cultivar was planted in large plastic pots (45 cm x 55 cm) and kept inside the green house at Coconut Research Institute, Lunuwila, Sri Lanka. Each pot was filled with Madampe series soils of Latosols which belongs to the land suitability class S1 of coconut growing soils. Six treatments were selected with three replicates 1 kg of Dolomite was added to all as the basal dressing. The treatments were: control (T1), inorganic fertilizer mixture (T2), BioGold® (T3), cattle manure (T4), Kochchikade biofertilizer (T5) and compost (T6). The growth performances of seedlings were measured by taking seedling girth, seedling height, number of leaves per seedling and total leaf area.

The measurements were recorded before and eight weeks after application of treatments. For the soil chemical analysis, soils were tested weekly for pH, EC (Electrical Conductivity) and macro and micro nutrients K, P and Mg. The microbial activities were also investigated weekly by measuring microbial biomass carbon and CO2 evolution.

The experiment design was a Complete Randomized with three replicates. The data were analyzed by analysis of variance (ANOVA) and significant means were compared by Least Significant Design (LSD) using the MINITAB statistical package. At the end of the research period no significant difference (P>0.05) was observed in growth parameters in any of the treatments. Similarly, none of the treatments were able to make a significant effect on soil pH (P=0.499) and EC (P= 0.100) throughout the research period. The significantly the highest available phosphorous (P) level was observed in inorganic fertilizer treatment and BioGold®, cattle manure, Kochchikade biofertilizer and compost also shown significant effects. A significantly high K level in soil after a six months period was shown by all the treatments except inorganic fertilizer treatment. Cattle manure contributed a significantly high level of Mg to the soil. By considering this result, it is possible to recommend cattle manure as a good fertilizer to increase the Mg level in a particular soil. A high acceleration of microbial activity was observed in BioGold® and the compost treatments. Cattle manure and Kochchikade biofertilizer had a similar effect with inorganic fertilizer showing the lowest activity. This implies that organic fertilizers are more environmental friendly compared to inorganic fertilizers. Although inorganic fertilizers are more fast and effective on increasing the available P in soil, in comparison to the organic and biofertilizers, they showed a negative impact on soil health. However, the contribution of inorganic fertilizer for K increment was not considerable. Therefore, it is important to consider all these facts before selecting a fertilizer to obtain the maximum benefit from coconut lands. Further, on recommending environmental friendly cost effective fertilizers, it is possible to recommend organic fertilizers as the environmental friendly and cost effective compared to the inorganic fertilizers.