quantifying hydrological effects of crop diversification in northern iran paddy fields

there are human and animal health concerns related to drainage systems because nutrients, especially nitrogen and phosphorus, can contaminate water supplies. a field study was conducted on consolidated paddy fields of sari agricultural sciences and natural resources university, northern iran (36.3°n, 53.04°e), to determine the effect of subsurface drain depth and spacing on nitrogen (n) and phosphorous (p) dynamics, the nutrients of most concern in eutrophication of receiving water bodies. during three successive rice -canola-rice growing seasons from july 2011 to august 2012, drainage and leaching losses of tn and tp were measured. tn and tp losses in untrained fields were 267 and 24.6 kg ha-1, respectively, while, such losses ranged from 41-50.6 for tn and 0.98-1.53 for tp, during the study period. the results showed that introduction of subsurface drainage in the study area, in addition to providing better condition for canola cropping and utilization of soil nutrients, considerably decreased nutrient losses.