EFFECT OF DIFFERENT SOURCES AND RATES OF NITROGEN AND SUPRA OPTIMAL LEVEL OF POTASSIUM FERTILIZATION ON GROWTH, YIELD AND NUTRIENT UPTAKE BY SUGARCANE GROWN UNDER SALINE CONDITIONS

The results of our pervious studies indicated that application of potassium @150 kg K2O ha-1 is effective in achieving economical sugarcane yield and optimum nutrient uptake under saline conditions. Keeping in view these findings, experiments were conducted on salt-affected soils at three sites of Punjab, Pakistan to select a suitable source and rate of N for obtaining optimum sugarcane yield and nutrient uptake from salt-affected soils. The experiments were conducted with two sugarcane varieties, salt tolerant (SPSG-26) and sensitive (CP-77400) using supra optimal level of K (150 kg K2O ha-1) as sulphate of potash SOP, P @ 100 kg P2O5 ha-1 as DAP (diammonium phosphate) and N @100 and 200 kg N ha-1 as urea or calcium ammonium nitrate (CAN). The results showed that cane length and diameter, number of tillers per plant, cane yield and sugar recovery increased with the application of N in both the sugarcane varieties under normal or saline conditions. Sugarcane growth and yield increased with increasing N rate from 100 to 200 kg N ha-1 in case of both urea and CAN. However, CAN as N source was more effective in enhancing sugarcane growth and yield than urea. The concentration of Na+ increased in both the sugarcane varieties due to salinity, however, application of K and N decreased its concentration. The combined application of NPK also significantly reduced Na+ uptake in leaves, however, the best combination observed was DAP+SOP+CAN. It was also observed that salt tolerant variety (SPSG-26) had lesser accumulation of Na+ than that of sensitive one (CP-77400). Application of N fertilizers significantly enhanced the nutrient (K, P, and N) uptake in both the varieties at both N rates (100 and 200 kg N ha-1) under normal as well as saline conditions. However, maximum uptake of nutrients was recorded at the highest dose (200 kg N ha-1) but CAN treated plants performed better than that of urea. On the basis of above results, the application of K as SOP and N as CAN was recommended for salt-affected soils to enhance the sugarcane yield. The salt tolerant variety for higher yield in salt-affected soil is also necessary for improving the cost benefit ratio. The results revealed that if salinity level of soil would exceed 10 dS m-1, considerable reduction in sugarcane yield could occur.