Effect of NPK Fertilizer Levels on Mineral Nutrition and Yield of Hybrid (Tall x Dwarf) Coconut

A field experiment was conducted at Coconut Research Station, Veppankulam during 2006-09 to asses the nutritional requirement of hybrid coconut (T x D) with 50 per cent nitrogen (N) substitution through organic manure. The experiment was conducted in 35 years old hybrid (T x D) palms (VHC 2). The experimental results proved that in hybrid coconut, a fertilizer level of 1000:250:2000 g NPK / Palm / year along with 50 kg of organic manure (Composted Coir Pith/ Vermi Compost) achieved economically higher mean annual nut yield, besides sustaining the soil fertility. While, the soil available NPK and index leaf NPK content was the highest at 1000:500:2000 g NPK/Palm / year. Considering consistent nut yield and sustainable soil health, 50 per cent of recommended N may be supplied through organic manure viz., vermicompost or composted coir pith and remaining 50 per cent N may be supplied through fertilizers. The organic manure that carries 50 per cent nitrogen can add organic matter to some extent in organically poor coastal coconut soils.

Coconut (Cocos nucifera Lin.) is an important plantation crop mainly cultivated in coastal belts of India.In general, coconuts survive for more than 60 years and continue to yield under ideal management conditions throughout the year and hence, require a continuous and balanced supply of nutrients for higher productivity (Upadhyay et al., 1998).Coconut palm absorbs large quantities of nutrients from the soil.A high proportion of mineral nutrients are removed from the soil by the coconut along with the harvested produce and debris.Application of fertilizers containing NPK and Mg at recommended rates partially compensates the depletion (Nadheesha and Tennakoon, 2008).Fertilizer requirement in coconut is generally assessed through computing the annual harvest of the nutrients by the palm or by studying the yield response to graded levels of applied fertilizers (Wahid, 1984).The annual nutrient removal by the coconut palms through nuts, fronds, trunk, bunch, spathe etc., varied from 20 to 174 kg N, 2.5 to 20.0 kg P2O5 and 35 to 49 kg K2O ha -1 (Ouverier and Ochs, 1978).The removed nutrients are to be replenished by one way or other for the sustainable coconut production.Hence, nutrient management plays a key role in determining the productivity of palms.
Either under nourishment or negligence of fertilizer organics to coconut or total dependence on chemical fertilizer often leads to poor productivity and leads to soil health deterioration.Hence, for sustaining the palm productivity and health of coconut soil, a judicious combination of organic manure and fertilizer nutrients are essential.Coconut based cropping system offers enormous scope for nitrogen substitution through organic manure by way of in-situ waste recycling through vermicomposting.The present experiment is contemplated mainly to supplement the chemical fertilizers with organic manures through vermicomposting / composted coir pith in coconut gardens.This may paves way for the gradual replacement of chemical fertilizers in coconut based cropping system in long run.

Materials and Methods
A field experiment was laidout at Coconut Research Station, Veppankulam in order to assess the nutrient requirement of hybrid coconut (VHC 2) with 50 per cent nitrogen (N) substitution through organic manures.The experimental site is located at 20m above MSL with average mean annual rainfall of 1,125 mm.The experimental soil was sandy loam in texture with a pH 7.1, EC 0.16 and organic carbon content of 0.20 per cent.The available NPK content of the experimental soil was low in N, medium in P and K ie., 118, 11.5 and 136 kg ha -1 , respectively.The palms were 35 years old and treatments consisted of each three levels of N (0, 500 and 1000 g / palm / year), P (0, 250 and 500 g / palm /year) and K (0, 1000 and 2000 g / palm /year) and totally there were 27 treatment combinations.Three palms were selected for each treatment and the experiment was conducted in a 3 3 non-replicated confounded factorial design.Based on the NPK content of vermicompost (1.4% N, 0.14% P and 0.29% K) and the composted coir pith (1.02: 0.60: 1.06 % and C: N ratio of 24.1), the required quantity of vermicompost or composted coir pith equivalent to 50 % N for each treatment along with P, K fertilizers (excluding the quantum of P, K supplied by the vermicompost -VC / composted coir pith -CCP) were applied as per treatments based on the avalilability of organic manure (CCP/VC).The above organic manure were applied in addition to the recommended Farm Yard Manure (FYM) ie., 50 kg/ palm/year.The fertilizers and organic manure (vermicompost / CCP) were applied in two equal splits, first during February and second during September of every year.The yield attributes viz., number of functional leaves, number of bunches produced, nut setting per cent, and nut yield for every treatment at the end of year were recorded.Besides, the soil available NPK and index leaf NPK content were estimated at the end of each year.

Effect of treatments on yield and yield attributes of coconut (Table 1 & 4)
The number of functional leaves recorded was significantly influenced by the NPK applied at graded levels.The number of functional leaves and bunches produced were in the range of 26 to 34 and 11 to 13 / palm, respectively among the NPK levels.Number of buttons produced was between 20.0 and 35.0 / Here, out of 1000 g of N, 500 g was supplied through composted coir pith or vermicompost based on availability.With regard to N and K, for every incremental addition of each nutrient, there was a corresponding increase in nut yield, whereas in case of P, the increase in nut yield was observed only up to 250 g / palm / year.Incremental addition of nitrogen, from 0 to 1000 g / palm /year, the increase in nut yield was from 146 to 158 nuts / palm / year (2008-09).For P level from 0 to 250 g / palm / year, the yield increase was from 144 to 156 nuts / palm / year and for K level from 0 to 2000 g / palm / year, the increase was from 136 to 165 nuts / palm / year (2008-09).Though there was some numerical variation among the various NPK levels, the trend of observation was similar in all the years of experimentation with respect to yield and yield attributes of coconut.The overall performance of palm could be improved by the application of NPK fertilizers at recommended level (Sudhakara and Nambiar, 1991).Rethinam et al. (1991) reported that integrated nutrient management increased the nut yield from 28 to 51 nuts / palm / year within three years.Integrated nutrient management is a handy tool for productivity increase and its sustenance in coconut garden (Hameed Khan, 2004).

Effect of NPK on soil fertility (Table 2)
Soil available NPK was appreciably increased for every incremental addition of respective nutrients (Table 2&3).Among the different levels of NPK, the highest soil available NPK was registered at their highest level tried i.e. 1000: 500: 2000 g of NPK / palm / year, though the economic nut yield was obtained at 1000: 250: 2000 g NPK / palm / year.This fact was true throughout the period of experimentation.The results on soil available NPK revealed that all the treatments recorded low status of available nitrogen, however there was some numerical difference between the treatments.Treatment combinations viz., T1 to T9 were found to have available nitrogen in the range of 101 to 117 kg ha -1 (2008-09) wherein, no nitrogen was applied.Among the treatments, from T10 to T18 that received 500 g N/palm / year registered the available N in the range of 142 to 152 kg ha -1 (2008-09).The higher available nitrogen was observed with the application of nitrogen at it's highest level i.e., 1000 g/palm/year (178 to 211 kg N ha -1 in 2008-09).Increasing the phosphorus level from 0 to 500 g/palm/year, progressively enhanced the P availability in soil.The available P content of 11.7, 19.0 and 22.7 kg ha -1 was recorded for P0, P250 and P500 levels respectively (2008-09).Similar increase in K level from 1000 to 2000 g/palm/year, enhanced the soil available K content from medium to high level (130 to 259 kg ha -1 2008-09).The effect of treatments on soil fertility status was almost similar in all the years of experimentation.Integrated nutrient management Index leaf nutrient content (Table 3) The index leaf nutrient (NPK) content was significantly influenced due to added levels of NPK as observed in other parameters.Hereagain, the highest leaf NPK content was observed with the application of NPK at their highest level viz., 1000, 500, 2000 g NPK, respectively, per palm per year.Enhanced nutrient release at the highest level of NPK and its subsequent absorption by the palm ultimately resulted in higher NPK in the index leaf, which may help in better photosynthesis and leads to better palm productivity.At the highest level of NPK i.e., 1000, 500, 2000 g / palm / year, respectively, the index leaf NPK content were also the highest.This proved the beneficial effect of INM in enhancing the leaf nutrient content.Similar observation was earlier made by Ghosh and Bandopadhyay (2009)

Conclusion
For hybrid coconut, a fertilizer level of 1000:250:2000 g NPK/Palms/year along with 50 kg FYM was found to be economical for achieving higher nut yield and sustaining the soil fertility.Considering consistent nut yield and sustainable soil fertility, 50 per cent of recommended nitrogen may be supplied through organic manure of either vermicompost or composted coir pith based on availability and remaining 50 per cent nitrogen may be applied as fertilizer.The soil available NPK and index leaf NPK content was highest at 1000:500:2000 g NPK/Palm/ year.This may pave way for the gradual replacement fertilizer in coconut based cropping system by way of in-situ waste recycling.