Impact of calcium sulphate and calcium carbide on nitrogen use efficiency of wheat in normal and saline sodic soils

pot experiment was conducted to study the effect of calcium as CaSO4 or CaC2 (20 mg Ca kg-1 of soil from each source) on N use efficiency of wheat (Triticum aestivum L. var. Inqlab-91) under normal (ECe=0.7 dS m-1, SAR=4.37 and pH=8.1) and saline-sodic soils (ECe=8.7 dS m-1, SAR=21.43 and pH=9.2) in glass house at National Agricultural Research Centre, Islamabad during Kharif season 2007-08. The crop was grown to maturity and data on tillering, plant height, panicle length, grains spike-1, straw and grain yields were recorded at the time of crop harvest. A considerable reduction in plant height (38%) and grain yield (44%) was observed when grown in saline-sodic soil (ECe=8.7 dS m-1) as compared to normal soil (ECe=0.7 dS m-1) while N application significantly improved plant growth and yield in both conditions. Among the treatments, N application even at lower rate supplemented with calcium as CaSO4, CaC2 or their mixture (1:1) showed better performance than that of straight N application in both soils. A 41 to 53% increase in plant growth and 36 to 44% in grain yield over control (without N) were observed through N fertilization at 25 and 50 mg kg-1 of soil supplemented with calcium as CaC2 in salinesodic soil. Similarly, calcium as CaSO4 application also caused a considerable improvement in plant growth (34 to 52%) and grain yield (25 to 43%). However, the effect of mixture application of CaSO4 and CaC2 (1:1) on plant growth and yield was comparatively more pronounced for both the soils. Interestingly, lower dose ofN (25 mg kg-1) with calcium as CaC2 alone or in combination with CaSO4 (1:1) supplementation showed statistically equal performance to that of higher dose (N=50 mg kg-1) alone. Tissue Na+ significantly decreased while K+ and Ca2+ concentrations were elevated due to N application along with calcium nutrition. Maximum N uptake and apparent N recovery were revealed from treatments where N was applied @ 50 mg kg-1 soil supplemented with calcium as CaC2 or CaSO4 alone or their mixture. A highly significant negative correlation (r = - 0.975) between dry matter yield and Na+ concentration and positive correlations (r = 0.8693 and 0.9396) betwe