Available nutrient status of a Typic Ustochrept as influenced by two irrigated and rainfed tropical agro-silvicultural plantations

An investigation was done during 1993-94 to study the effect of 10-year old irrigated and rainfed plantations of Eucalyptus tereticornis Smith and Leu ceana leucocephala (Lam.) de Wit on available nutrient status of 2 related soil series belonging to Typic Ustochrept with the hypothesis that unless p roperly managed, those fast growing species may degrade the soil fertility in a long run. Raising either crops under rainfed condition depleted all th e major nutrients and zinc over fallow both at the surface and down the pro file. Among the plantations Eucalyptus preserved N and K better than Leucea na while the latter was superior with relation to P and secondary nutrients ; micronutrients not showing any definite trend. Results could be explained in terms of nutrient demand, nutrient fixation in standing plantations and renewal through leaf fall and litter formation. Biomass and nutrient harve sted/recycled data is expected to provide further insight to the problem. P ot culture experiment with upper 30 cm soil and 'HD 2428' wheat (Triticum a estivum L. emend. Fiori & Paol.) as a test crop corroborated the field stud y. Soil under irrigated Eucalyptus gave wheat grain yield at par with treat ment having recommended fertilizer dose in fallow while that under Leuceana was significantly lower. Available N, P, K and Zn were found to be importa nt controlling factors towards wheat grain yield.