Foliar diagnosis in coconut (Cocos nucifera, Linn.) in relation to nitrogen, phosphorus and potassium

Abstract

A study was undertaken to standardise the foliar diagnostic technique in coconut palm in relation to nitrogen, phosphorus and potassium, making use of the experimental palms of a permanent NPK trial maintained at the Coconut Research Station, Balaramapuram, Trivandrum District. The palms of this experiment received applications of nitrogen, phosphorus and potassium in three levels each viz., 0, 340 and 680 g nitrogen per palm per year, 0, 225 and 450 g P2O5 per palm per year and 0, 450 and 900 g k2O per palm per year. For the standardization of tissue for foliar diagnosis, samples of leaf lamina and mid-rib were drawn separately from all the leaves of the experimental palms. Attempts were also made to establish critical levels of nitrogen, phosphorus and potassium in the leaf and also to work out regression models to predict yield based on the tissue content of these nutrients. Observations revealed that the number of leaves retained by the palm was mainly a function of potassium applied. The number of leaves retained by the palm significantly correlated with the yield(r = 0.93**). The potassium content of lamina of the 2nd leaf can be predicted from the number of leaves retained, making use of the regression equation, Y = 5.32 + 8.95 x where x is the potassium per cent of leaf lamina and Y is the number of leaves retained. The number of leaves retained was also found to be significantly correlated with yield (r = 0.708**). The percentage of nitrogen in the leaf lamina increased with increasing age of leaf till leaf number 6 and thereafter steadily declined. The phosphorus and potassium contents of the leaf were maximum in the youngest leaf and declined with increasing age of leaf. Palms receiving higher levels of nitrogen and potassium retained correspondingly higher contents of nitrogen and potassium in leaf lamina. Application of different levels of phosphorus gave only marginal difference in the percentage of phosphorus in leaf lamina. The nitrogen content of leaf lamina of different leaf position was significantly correlated with yield, the highest coefficient of partial correlation of 0.777** being registered for the 10th leaf, followed by 0.699**for the 2nd leaf. The phosphorus content of leaf lamina failed to establish significant correlation with yield, irrespective of leaf positions. The coefficients of partial correlation between yield and potassium per cent of lamina of leaf positions 2, 3, and 6 were significant, the highest value of 0.663** being recorded for the second leaf. Taking the percentage of nitrogen (N) and potassium (K) in the lamina of 2nd leaf and leaf number (L) as independent variables, yield can be predicted with an accuracy of 84 per cent (R2 = 0.84**) by the regression model, Y = -14.956 + 39.215 N – 16.097 N2 + 83.873 K – 37.388 K2 -11.046 L – 0.202 L2 – 44.186 N x K + 5.529 N x L + 6.276 K x L. The yield can also be predicted with an accuracy of 72 per cent by the regression model, Y = -64.29 + 23.356 N + 1.779 L where N is the nitrogen percentage of lamina of 2nd leaf and L is the number of leaves retained. The critical values for nitrogen and potassium in the leaf lamina of 2nd leaf were found to be 3.31 per cent for nitrogen and 2.17 per cent for potassium. The pattern of distribution for nitrogen, phosphorus and potassium in the leaf mid – ribs was almost similar to the pattern of distribution of those nutrients in the leaf lamina. The coefficients of partial correlation between yield and nitrogen content of leaf mid-rib of leaf positions 6, 14, 15 and 18 were statistically significant, the highest value of 0.677** being recorded for the 14th leaf. The phosphorus content of mid-rib failed to establish significant correlation with yield. The coefficients of partial linear correlation between yield and potassium per cent of mid-ribs were significant for leaf positions 1, 2, 3, 4, 5, 6, 7 and 10, the highest value being recorded for the 4th leaf (r = 0.762**). The multiple correlation coefficient between yield and percentage of nitrogen, phosphorus and potassium was highest (R = 0.771**) for the lamina of the second leaf, among all the position and types of tissue examined and hence, this tissue is recommended as the best tissue for the foliar diagnosis of nitrogen, phosphorus and potassium.