Nitrogen Use Efficiency In Rice Wheat Cropping System In Different Types Of Salt Affected Soils Receiving Gypsum

Considerable nitrogen (N) losses lead to lower N use-efficiency (NUE) in salt-affected soils due to leaching and volatilization. A lysimeter experiment was conducted to determine NUE in two salt-affected soils of different texture (clay loam and sandy clay loam), using various rates of N fertilizer. The experiment used a three replicate completely randomized design. The treatments included five N rates, three higher (15, 30 and 45%) and two lower (15 and 30%) than recommended rate of 125 kg ha-1. Additionally, gypsum was added at 50 and 100% of soil gypsum requirement (SGR) in both salt-affected soils. Maximum paddy and straw yields were recorded for sandy clay loam saline-sodic soil collected from Village 132, Faisalabad (132S), using 45% higher N + gypsum at 100% SGR. Whereas clay loam saline-sodic soil, from Village 84, Faisalabad (84S) at 30% higher N rate with gypsum at 50% SGR gave the highest paddy and straw yields. In general, the clay loam soil produced more paddy yield than the sandy clay loam soil at similar N fertilization. In the sandy clay loam soil, gypsum at 100% SGR along with a 30% higher N rate increased the grain and straw yields of wheat significantly (p < 0.05) compared to application of gypsum at only 50% SGR. Nitrogen use efficiency was the highest with 45% higher N (N145) with gypsum applied @ 100% SGR compared to 50% SGR in severe salt-affected (sandy clay loam) soil during rice crop. From marginal clay loam saline-sodic soil, NUE remained higher with N130 along with gypsum @ 100% SGR which was statistically on par with gypsum @ 50% SGR. It was concluded that NUE remained highest with N130 and N145 with gypsum applied @ 100% SGR during rice crop from clay loam and sandy clay loam soils, respectively. Moreover, NUE was higher at recommended N fertilization when gypsum was applied at 100% SGR which was also attributed to improved soil chemical properties, i.e. pHs, ECe and SAR.A field experiment was conducted at Village 132/ GB and 84/ GB to determine NUE in the two salt-affected soils of contrasting texture (clay loam and sandy clay loam), using higher rates of N than that in their counterpart normal soils. The experiment was laid-out in a randomized complete block design with three replications. The promising treatments were selected from lysimeter experiments for field experimentation. The treatments employed for normal soils were: No fertilizer (C), recommended N fertilizer (N100), 15% higher N than recommended N fertilizer (N115), 30% higher N than recommended N fertilizer (N130). The treatments selected for salt-affected soils were: No fertilizer and no gypsum (C), recommended N + gypsum @ 50% SGR (N100+G50), 30% higher N than recommended N fertilizer + gypsum @ 50% SGR (N130+G50), recommended N + gypsum @ 100% SGR (N100+G100), 30% higher N than recommended N fertilizer + gypsum @ 100% SGR (N130+G100). The highest NO3- leaching was recorded with N130 along with gypsum @ 100% SGR from clay loam (84S) and sandy clay loam (132S) salt-affected soils. During wheat crop, more NO3- concentration in leachate was recorded compared to those during rice crop. The crop yield was lowered from salt-affected soils during amelioration by using higher rates of fertilizer (N130) and gypsum application compared to their counterpart normal soils. The 30% higher N than recommended with gypsum @ 50% and 100% SGR improved (salt-affected soil) properties and crop yields from clay loam (marginal SA) and sandy clay loam (highly SA) soils, respectively. During early stages of reclamation, higher doses of N and gypsum are required to achieve maximum economical yield and NUE. During 2nd year, NUE was the highest with recommended rate of N and gypsum @ 50% and 100% SGR for clay loam and sandy clay loam soils, respectively. The greatest decrease in yield gap from sandy clay loam and clay loam saline-sodic soils was observed with 30% higher rate of applied N along with gypsum @ 100% SGR and 50% SGR, respectively