Somasiri, L.L.W.

Tennakoon, N.A.

Coconut Research Institute Repository

O R G A N I C M A N U R E S : A P O T E N T I A L M I C R O N U T R I E N T S O U R C E F O R C O C O N U T The elements which are required in very small amounts but essential for plant growth are known as micronutrients or trace elements. Eight such elements viz manganese (Mn), iron (Fe), boron (B), zinc (Zn), copper (Cu), molybdenum (Mo), cobolt (Co) and chlorine (Ci) have been recognized as micro-nutrients for plant growth. The coconut palm takes up nitrogen (N), phosphorus (P) and potassium (K) in large quantities as primary nutrients and the magnesium (Mg) and sulphur (S) in moderate quantities as secondary nutrients. Chlorine (CI) is also removed by the coconut palm in a large quantity which is comparable to potassium. The soil may get rapidly depleted of these nu­trients due to prolonged coconut cultivation. Therefore potassium and magnesium defi­ciency symptoms are often visible in coconut plantations. Such deficiencies can be corrected by application of common NPK and Mg fer­tilizers. Micronutrient deficiency symptoms in coconut plantations have not been observed so far except boron (B) in very few sites. In 1980's, the boron deficiency symptom first ap­peared in coconut palms on a heavily leached soil at Pujapitiya, in Kandy district. Later the boron deficiency symptoms appeared in Kegalle and Peradeniya areas in 1993, where coconut has been planted in uprooted rubber lands. "Visible symptoms occur in the leaf only when the deficiency is severe. When the N A Tennakoon L L W Somasiri Coconut Research Institute of Sri Lanka deficiency is mild, symptoms are not visible but yield limiting conditions would occur. In such circumstances, deficiencies should be diagnosed by special techniques. Nutrient de­ficiencies of the coconut palm can be diag­nosed easily by analysing the leaf nutrient con­centration of the 14th frond. Sufficiency ranges of concentrations of primary and sec­ondary nutrients are well established. Suffi­ciency ranges for few micronutrients have been determined by some workers and those for other micronutrients are under investiga­tion. The sufficiency ranges of micronutri­ents for the coconut palm are as follows. Mn - 60 mg/kg B - 8-10 mg/kg Fe - 40 mg/kg Cu - 5-7 mg/kg Zn - 15-24 mg/kg CI - 3000-6000 mg/kg (Manciot et al., 1979; Eschbach and Manciot, 1981; ANON, 1989). The leaf analysis of coconut palms grown on some predominent soil types in the major coconut growing areas, such as Madampe series, Sudu series, Andigama se­ries, Kuliyapitiya series, and Kurunegala se­ries indicated that Fe and Mn concentrations were above the respective sufficiency ranges in all five soil series. The study further showed that leaf Cu concentration of coconut in all 1 five soil types was marginal. The leaf zinc concentration was also marginal in Kuliyapitiya and Kurunegala soil series. Low concentrations of leaf boron were randomly observed in all soils irrespective of the soil type (Somasiri, 1994). Therefore, the situa­tion is not alarming to the extent that micro-nutrient fertilizers to be applied to coconut. But the current situation suggests that appli­cation of organic manures to coconut could be a successful preventive measure against oc­currence of micronutrient deficiencies of co­conut plantations in the future. Organic manures are rich in micronu-trients as shown in Table 1. Trace elements in organic manures occur in complex forms. They are released to the soil at a slow rate de­pending on the rate of decomposition of or­ganic matrix (Tennakoon, 1994). Most or­ganic sources are applied to the coconut palm at the rate of 30 kg per palm per year, except goat dung which is applied at the rate of 15 kg per palm per year (Anon, 1987). Obviously, organic manures can be success­fully used for replenishing the soil micronu­trient pool. Although the current recommen­dations on organic manures for coconut (eg. Table 1 Micronutrient concentrations in different types of organic sources (Tennakoon, 1994) Organic source Micronutrients ppm (mg/kg) Fe Mn Cu Zn B Goat dung 1449-2174 246-505 20-38 112-184 29-66 Cow dung 690-1518 167-389 24-40 128-183 13-30 Poultry manure Broiler Litter Layer Litter 723-1565 1144-2215 213-421 287-450 27-40 22-38 166-271 182-329 15-27 12-23 Pig dung . 1020-1990 180-207 45-48 186-575 4-13 Farm yard manure (FYM) Compost 1135-3515 2090-4064 229-668 201-505 17-29 11-25 83-128 . 75-169 12-27 12-20 Biogas residues 1097-1644 402-616 37-53 300-412 22-46 Sewage sludge 2275-3322 100-287 7-11 69-177 3-5 Gliricidia 212-450 85-156 4-5 57-70 41-69 Acacia 870-994 78-92 7-9 54-61 46-49 Pueraria 117-280 82-120 4-6 64-70 20-24 2 A p p l i c a t i o n o f o r g a n i c m a n n u r e 35 kg of cattle manure, or 30 kg of poultry ma­nure or 15 kg of goat dung) are aimed at meet­ing the N demand of the palm. The same amount would be sufficient to enrich the soil micronutrient pool. It is important to note that accumulation of micronutrients in the soil would become toxic to plants. Such an accu­mulation could result from liberal application of micronutrients. Therefore, much care is needed in using micronutrient chemical fertil­izers. Whereas addition of micronutrient through organic would not cause such an ac­cumulation due to their slow decomposition. Therefore organic manure application would be safer and more beneficial than chemical fertilizer application to the coconut palm be­cause it supplies the required amount of pri­mary and secondary nutrients along with mi­cro nutrients. Improvement of soil quality around the coconut palm is another impor­tant benefit of organic manuring. R e g i s t e r w i t h C R I C o c o n u t c u l t i v a t i o n i s v e r y p r o f i t a b l e i f y o u d o i t c o r r e c t l y w i t h n e w t e c h n o l ­o g y . T h e C o c o n u t R e s e a r c h I n s t i t u t e h a s d i f f e r e n t p r o g r a m m e s t o a s s i s t c o c o ­n u t g r o w e r s t o i m p r o v e t h e i r k n o w l e d g e o n c u l t i v a t i o n a n d p r o c e s s i n g . C o c o ­n u t g r o w e r s a r e r e q u e s t e d t o r e g i s t e r w i t h t h e i n s t i t u t e t o o b t a i n t h e s e s e r v i c e s . P l e a s e s e n d y o u r i n f o r m a t i o n t o t h e D i r e c t o r , C o c o n u t R e s e a r c h I n s t i t u t e , L u n u w i l a . 3 

Organic manures. a potential micronutrient source for coconut