PhD

A study on the applicability of diagnosis and recommendation integrated system (DRIS) in coconut palm (Cocos nucifera L.) was conducted at the department of Agronomy, college of Horticulture, Vellanikkara during 1991-’94. The study was conducted using coconut population of var. West Coast Tall being maintained at three research stations of Kerala Agricultural University namely, Regional Agricultural Research Station, Pilicode; Agricultural Research Station, Mannuthy and Coconut Research Station, Balaramapurm.
Eight hundred palms varying in their yield from 5.8 to 162.7 nuts per palm per year were selected for developing DRIS norms. Leaf samples were collected from the 14th frond and were analysed for macro and micronutrients namely N, P, K, Ca, Mg, S, CI, Fe, Zn and Mn employing titrimetric, spectrophotometric, flame photometric or atomic absorption spectrophotometric method depending on the element. DRIS norms were developed using the data generated from the chemical analysis of leaf samples using the methodology of Beaufils (1973). The palm population was divided into low-and high-yielding subpopulations. The means and variances of nutrient concentration as well as their ratios (totalling 90 including inverse ratios) were worked out for the two subpopulations. The variance ratios were then computed for each nutrient and each nutrient ratio to examine their statistical significance and those discriminating significantly between the two subpopulations were considered for DRIS norms. When both the ratio and its inverse form were significant, the one which had a higher variance ratio was selected. Mean values of the selected individual nutrients and nutrient ratios of the high yielding sub population formed the DRIS norms.
Five nutrients and 33 nutrient ratios were selected on the basis of higher variance ratios as DRIS norms. Thirty one DRIS charts involving selected three-nutrient combinations can be constructed from the selected nutrient ratios. A qualitative assessment of nutritional imbalance involving three nutrients is possible by utilising these DRIS charts.
DRIS technique also provides another approach that can accommodate any number of nutrient ratios in which nutrient indices are worked out using DRIS norms and the observed nutrient ratios for the plant under test. The DRIS index for a nutrient indicates its relative abundance among the nutrients considered in its computation. Lower the value of the index for a nutrient, greater is its requirement.
The accuracy of diagnosis of nutritional imbalance by DRIS approach was tested for ten selected nutrients in palm receiving varying levels of NPK under a factorial experiment. From this it was observed that DRIS index for a nutrient varied not only with the applied level of that nutrient but also with the applied level of other nutrients and an improvement in yield with increase in DRIS index value was obtained for the application of K. The overall nutritional balance of a palm is given by the nutrient imbalance index (NII) which is the sum of the nutrient indices irrespective of the sign. A strong negative relationship was observed between this NII and yield.
DRIS norms developed on the basis of different yield cut-off values showed that they were affected by the criterion used for dividing the population into low-and high-yielding groups. Similarly DRIS norms developed for different soil type as well as for different climatic situations under the same soil type had also shown variations indicating their influence on DRIS. A comparison of DRIS approach with critical level approach indicated that DRIS could supplement information on balance or imbalance of nutrients in coconut palm and it could be used beneficially in nutrient management programmes in conjunction with critical level approach.