Utilization of waste office paper to reduce nitrate leaching into the Northern Guam aquifer

 Rapid nitrate leaching losses due to current agricultural N management practices under the humid tropical environmental conditions of the Pacific island of Guam may contaminate fresh and salt water resources. Potential environmental contamination of the Northern Guam aquifer, which is overlain by shallow limestone-derived soils, is a major public concern because the aquifer is the sole underground source of fresh water for the island. The objectives of this study were to examine the use of waste office paper as a possible management alternative for reducing nitrate leaching due to N fertilizer applications in northern Guam while also providing sufficient N for crop growth. In a laboratory study, increasing rates of waste paper application reduced NO₃ ^–-N leaching up to approximately 200 days after incorporation of N fertilizer and paper treatments. Subsequent mineralization of immobilized N from paper applications was also observed, although cumulative NO₃ ^–-N leaching at the highest rate of paper addition was lower than the control after 394 days of incubation. The effect of waste paper on N availability and NO₃ ^–-N leaching after application of N fertilizer at rates up to 500 kg N ha^–1 was also evaluated in two field experiments planted with sweet corn (Zea mays var. rugosa Bonaf.) during consecutive dry and wet periods. Leaching losses of NO₃ ^–-N were higher during the wet cropping season, leading to lower crop yields and crop N uptake. Combining paper with N fertilizer reduced NO₃ ^–-N leaching losses but also decreased crop ear yields up to N fertilizer application rates of 250 kg N ha^–1 during the dry cropping season and up to rates of 100 kg N ha^–1 during the wet period. Although combining waste paper with N fertilizer reduced NO₃ ^–-N leaching losses, no improvements in fertilizer N recovery were observed during the field experiments. This lack of crop response may be due to the importance of early season N availability for the short-season horticultural crops grown on Guam. We suggest that the application of waste paper may be a useful management practice to reduce NO₃ ^–-N leaching losses when high soil NO₃ ^–-N levels remain after cropping due either to crop failure or to over-application of N fertilizer. Received: 11 May 1999