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

A 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 saline-sodic 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 of N (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 Ca^2+ 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) between dry matter yield and K^+ and Ca^2+ concentrations, respectively in plant tissues was observed in saline-sodic soil.