Seasonal dynamics of mineral N pools and N-mineralization in soils under homegarden trees in South Andaman, India

Agroforestry trees are now well known to play a central role in the build up of nutrients pools and their transformations similar to that of forest ecosystem, however, information on the potential of homegarden trees accumulating and releasing nitrogen (mineralization) is lacking. The present study reports seasonal variations in pool sizes of mineral N (NH ₄ ⁺ -N and NO ₃ - -N), and net N-mineralization rate in relation to rainfall and temperature under coconut (Cocos nucifera L.), clove (Eugenia caryophyllata Thunb) and nutmeg (Myristica fragrans Houtt. Nees) trees in a coconut-spice trees plantation for two annual cycles in the equatorial humid climate of South Andaman Island of India. Concentration of NH ₄ ⁺ -N was the highest during wet season (May-October) and the lowest during post-wet season (November-January) under all the tree species. On the contrary, concentration of NO ₃ - -N was the lowest in the wet season and the highest during the post-wet season. However, concentrations of the mineral N were the highest under the nutmeg and the lowest under the coconut trees. Like the pool sizes, mean annual mineralization was the highest under the nutmeg (561 mg kg-¹ yr-¹) and the lowest under the coconut trees (393 mg kg-¹ yr-¹). Rate of mineralization was the highest during the post-wet season and the lowest during the dry season (February-April) under all the tree species. High rainfall during the wet season, however, reduced the rate of nitrification under all the tree species. The mean annual mineralization was logarithmically related with rainfall amount and mean monthly temperature.