PhD

A study on “ Integrated nutrient management in cashew in relation to yield and quality” was taken up during 1995-1999 at College of Horticulture, Vellanikkara. It consisted of five experiments to find out the litter contribution and the nutrient return through cashew litter, to compare the litter production in the fertilized and unfertilized plots, to evaluate the effect of AMF, Azotobacter and Azospirillum on growth and establishment of cashew in the nursery and main field and also to know the interaction effect of these biofertilizers on cashew.
The average annual litterfall in ten year old cashew plantation was 5014 kg ha-1. Litter contribution varied with the season and variety. Dry months contributed to the major share of annual litter production. Decomposition studies of leaf litter revealed that there would be over 90% weight loss within 21 months after litterfall. Correlation between leaf litterfall, decomposition and weather parameters was worked out. The nutrient content of the litter from a normally fertilized garden was estimated to be 0.65%N, 0.22%P, 0.72%K, 0.22%Ca, 0.19%Mg, 369ppm Fe, 17ppmZn, 15ppmCu and 283 ppmMn and the nutrient return was calculated as 32.1kgN, 1.1 kgP, 36.5 kg K, 10.9 kg Ca, 9.5 kg Mg, 2.1 kg Fe, 0.1 kg Cu and Zn and 1.2 kg Mn per hectare.
The average annual litter production in the unfertilized plot was 3235 kg ha-1. The average composition of litter from unfertilized plot was 0.71%N, 0.03%P, 0.63%K, 0.19%Ca, 0.14%Mg, 230 ppm Fe, 17 ppm Cu, 12 ppm Zn and 469 ppm Mn. There was no significant difference in the nutrient content of the fertilized and unfertilized plots. Fertilizer application led to an increase in the organic carbon content of the soil.
AMF inoculation enhanced the growth and uptake of cashew seedlings in the nursery. G. intraradices inoculated plants were superior among the six species of AMF tested. The same trend was observed in seedlings and grafts when planted in the field. AMF inoculation enhanced the absorption of 32P labeled fertilizers.
Azotobacter and Azospirillum inoculation enhanced the germination, growth and development of cashew seedlings in the nursery. In general, Azospirillum inoculated plants were more efficient than Azotobacter inoculated cashew plants. The same trend was observed in the seedlings and grafts planted in the field.
Combined inoculation of AMF and Azospirillum was found to be the best among the different combinations tried in the nursery.
An increase of 24.03% in yield due to combined inoculation of Azotobacter and Azospirillum could be observed in twelve years old cashew trees.