Intensive cropping and groundwater quality deterioration
1997
Gumtang, R.J. | Bucao, P.S. | Taclan, L.B. | Pampolino, M.F. | Castaneda, A.R. | Troung, T.P. | Bhuyan, S.I. (Mariano Marcos State Univ., Batac, Ilocos Norte (Philippines))
A case study was conducted in a semiclosed watershed of about 265-ha located at Bgy. [village] Magnuang, Batac, Ilocos Norte [Philippines] to assess groundwater quality in relation to land use and fertilizer N inputs. The GLEAMS (Groundwater Loading Effects of Agricultural Management Systems) model was used to estimate the nitrate residue expected in the root zone that will eventually reach the groundwater. The cropping practices in the area showed an accumulation of about 200 kg N/ha in the soil which could increase the nitrate level in shallow groundwater by about 1 ppm per year. The salinity levels (700-3000 umho/cm) in all wells exceeded the FAO's threshold quality for irrigation. According to FAO, wells with this salinity level could no longer sustained the crop to give maximum yield. Eight wells showed near or above WHO's nitrate limit (10 ppm) for drinking water, rendering its usage for human consumption. An average of about 11 ppm nitrate is detected in areas where rice-sweet pepper was practiced, while 28 ppm nitrate was detected in sweet pepper-fallow cropping system. Nitrate concentration in groundwater may be reduced by planting deep-rooted cash crops such as indigo, corn, and mungbean during the dry to wet transition period; applying fertilizer in three to four splits following the recommended application rate; and moderate restrictions of the use of tubewells for irrigation by applying small amount of irrigation water at more frequent intervals
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