It is well known that N and K has synergistic effects. Deficiency of one element might create detrimental effect of other element on crop growth and development. In this regards, under K control condition, I have found lower rice yield with N application than N control.
Dear Dr. Islam,
You may adopt soil test based recommendation for these nutrients (N, P, K and Zn etc.). The needed total amount of K should be applied basally i.e. at the time of transplanting. Use 1/3 of N fertilizer (ammonical fertilizer or urea as N source) at the time of transplanting and remaining amount of N through top dressing in three or more splits. The reason for getting very low yields with N with out K fertilizer could be due to more accentuated demand for K by the crop.
Dr Prakash
Thank you for you answer. So far I understand, you advocated K should be applied according to soil test results and then N should be applied in splits.
I want to know more about what will be happen if we apply N in K deficient situation?
@ Islam
I guess added N is taken up by soil minerals like high charge smectite or low charge vermiculite,which greatly adsorb/fix NH4 ions available through N fertilizers.It is better to add K as basal dose and then application of N may be initiated as Dr. Srivastava suggested.. Some detailed information of clay mineralogy by XRD especially with K-saturated clay samples heated at 110/300/550 degree C will be of much help.
Dear Dr. Islam,
The case of extreme deficiency of K encountered in this case must be due to very high K fixation capacity of the soil as pointed out by Dr. Pal. Addition of NH4+ source may replace some K ions from clays with the fixation of added NH4+ ions through ammonical fertilizers as both ions have similar fate in K fixing soils. However, addition of N without K would lead to more K stress in the crop due to dilution effect happening upon enhanced vegetative growth of the crop caused by N fertilization alone. Potassium stress would make the crop more succulent and desiccated due to poor stomatal regulation of transpiration, poor partitioning of little carbohydrate synthesized under K deficient situation. Such crop would also be more prone to insect and disease attack and also lodging losses.
The practical solution of the problem involves required addition of K to soil to satisfy the K fixing capacity of the soil and maintaining sufficient amount of exchangeable K on the exchange complex of soil. Foliar spray of potassium sulphate solution (2%) at 10-15 days interval can be used as a contingent measure to immediately recover the crop from extreme K deficiency stress.
Dr. Islam, plants require potassium ions for protein synthesis and for the opening and closing of stomata, which is regulated by proton pumps to make surrounding guard cells either turgid or flaccid. A deficiency of potassium ions can impair a plants ability to maintain these processes. Therefore application of N can not help this much unless and until you apply potassium. Potassium also function in other physiological processes such as photosynthesis, protein synthesis, activation of some enzymes, phloem solute transport of photo-assimulates into source organs, and maintenance of cation-anion balance in the cytosol and vacuole. Therefore, you need a balance of N and K application. In general, potassium deficiency is common in light, sandy soils, because potassium ions are highly soluble and will easily leach from soils without colloids. Potassium deficiency is also common in chalky or peaty soils with a low clay content and on heavy clays with a poor structure.
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