| The contribution of annual litter and the nitrogen mineralization rates (NMIN) in the field and in the laboratory were quantified. Three ecosystems were evaluated: (1) unshaded coffee (CSL); (2) shaded coffee (CSM), and (3) secondary forest (BQS) in the municipalities of Jayuya (Oxisol), Lares (Inceptisol) and Las Marias (Ultisol), respectively. The dry matter and N input in litterfall was quantified from monthly samples during a twelve month period and from the N concentration in litterfall. The highest litterfall input was in CSM, followed by BQS, and CSL with mean values of 2.2, 1.8, and 1.4 ton dry matter ha-1 yr-1, respectively. The largest litter N contribution was in CSM in the three locations with average 52 kg N ha-1 yr-1 followed by BQS with 44 kg N ha -1 yr-1. Field N mineralization in Las Marias was significantly higher in BQS and CSM than CSL. The cumulative NMIN extrapolated on an annual basis was 102 kg N ha-1 yr-1 in BQS, 96 kg N ha-1 yr-1 in CSM, and 49 kg N ha -1 yr-1 in CSL. Under laboratory conditions the N mineralized in 17 weeks was significantly higher in CSM and BQS than CSL with values of 42, 38, and 34 kg-1 N ha-1, respectively. The N contribution from litterfall was 34, 60 and 55% of the total N mineralized in CSL, CSM, and BQS, respectively. Nitrogen mineralization was higher in the laboratory than in the field due to soil disturbance during sieving. The greater soil N mineralization in forest and shaded coffee demonstrates decreased ecosystem sustainability in sun-grown coffee. |
