Nitrate-N Leaching Losses into Field Tile Drains as Affected by Irrigation Regime and N-Fertilizer Doses in Clay Soil under Maize Plant

A field experiment was conducted at Sakha Res. Station, Kafr El-Sheihk Governorate during summer seasons (2017and 2018), to evaluate the effect of irrigation regime (i.e: traditional irrigation and cutoff irrigation when it reaches to 85% of furrow length) and applied N-fertilizer doses (one, two and three doses) on nitrate leaching losses into field tile drains in clay soil as well as productivity of irrigation water, yields and N-uptake of maize plant. The obtained results indicated that: Cutoff irrigation received the lowest amount of irrigation water and drain discharge rates. Cumulative amounts of drainage water were lower with cutoff irrigation than that observed under traditional irrigation. N-fertilizer application in two and three doses especially, with cutoff irrigation resulted in moderate increased of soil NO₃^- content after every dose and slightly decreased after the followed irrigations while, one dose application resulted in the highest values of NO₃^- content in the soil and rapidly decreased after the followed irrigations. N-fertilizers application in two or three doses resulted in decrease of nitrate concentration and losses in drainage water than the addition of one dose especially, under cutoff irrigation. The estimated losses of NO₃^- or N-NO^-₃ in drainage water were increased when addition of N-fertilizer in one dose than two and three doses by 12.42 and 16.51% in the first season of study and 13.33 and 16.54 % in the second season, respectively under cutoff irrigation. The corresponding percentages were 19.02 and 22.04% in the first season and 19.12 and 22.88 % in the second season, respectively under traditional irrigation. N-fertilizer application in three and two does led to an increase in maize grains yield by about 14.84 and 10.59 % in the first season and 14.84 and 11.26 % in the second seasons, respectively as compared to one dose. Cutoff irrigation tends to increase maize grains yield by 2.44% in the first season and 2.13 % in the second season than traditional irrigation. The combination between irrigation and N-fertilizer doses data showed that, both irrigation treatments with addition of N-fertilizer in three doses resulted in relatively higher yield of maize (3470 kgfed.^-1) followed by two doses (3318 kgfed.^-1, ) while, the addition of N-fertilizer in one dose with both irrigation treatments resulted in relatively low yields (2955 kgfed.^-1). The higher values of N-uptake and productivity of irrigation water for maize yields were found with cutoff irrigation with three doses in both seasons of study and the lower values were obtained with traditional irrigation with one dose.