López-Ramos, Litza Y.

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    Descomposición de leguminosas coberturas en un oxisol en Isabela, Puerto Rico
    (2011) López-Ramos, Litza Y.; Valencia-Chin, Elide; College of Agricultural Sciences; Whitmire, Stefanie L.; Román Paoli, Elvin; O'Farrill, Hipólito; Department of Crops and Agro-Environmental Sciences; Borges, Sonia
    Lablab purpureus cv. Rongai and Mucuna pruriens (dwarf mucuna) are used as cover crops because of their beneficial contribution to physical and chemical soil properties. Two studies were conducted at the Agricultural Experimental Sub-station of Isabela, University of Puerto Rico. 'Rongai' and dwarf mucuna were seeded on an Oxisol of the Coto series at 10 kg ha-1 of density. The first study evaluated the influence of two planting seasons (dry and wet) on the fresh leaf tissue decomposition and the residual N content. Dry matter yield ranged from 3785 to 5535 kg ha-1, with the highest level found for 'rongai' in the dry season. The decomposition rate was higher for the 'rongai' tissue compared with mucuna, indicating that the 'rongai' decomposition was faster. The N content in the dry matter was higher in the wet season (2.70%) than the dry (2.28%), and higher in mucuna (2.59%) than 'rongai' (2.38%). There was also a season by legume interaction on the N content in the leaf tissue, where the highest value was obtained for mucuna in the dry season (65μg /g). This is not surprising since 'rongai' decomposed faster. There was also an interaction on N content between season and bag position, where the higher mean value was obtained in the bags placed on the ground for the wet season (77μg /g). The same interaction was found with organic matter percent, where the higher average value was obtained for the bags positioned on the ground in the wet season (75%). Both of these suggest that less N is lost during the leaf decomposition on the soil surface during the wet season. This is further supported by the interaction between legume and bag position, where the highest value of organic matter was obtained for mucuna in the bags positioned above-ground (78%). The second study evaluated the mineralization and nitrification rate of mucuna and 'rongai'. N mineralization rates changed over time in all plots. Negative N mineralization values where found for 22 and 42 days of incubation, indicating N immobilization. However, the highest N mineralized was found after 90 days of incubation, this means that it will be available for plant use after this time. Net nitrification rates were highest in the 22 day incubation with 'rongai' indicating high content of nitrate in these plots. Negative values after this time indicate slow nitrification because the high content of ammonium. In summary, both legumes represent an alternative to improve soil fertility, as both showed good yield and acceptable residual concentrations of N, organic C and OM. The use of these legumes as a green manure at least 90 days after planting would allow farmers to take advantage of its mineralization.