There are many tools for fertilizer recommendation except soil test. One of the most important tool is Site specific nutrient management (SSNM). Another is leaf color chart (LCC) for N fertilizer recommendation. I gaze there may be more tools for fertilizer recommendation.
Dear Dr. Islam,
(1) Recommendations of fertilizer applications to crops are best done on the basis of (a) soil tests for nutrients availability, and (c) the target yield level and nutrients requirement of crops. When no laboratory facility for soil tests is not available, fertilizers may be recommended on the basis of visual symptoms of nutrient deficiency exhibited by the crops.
(2) As diagnosis of nutrient deficiencies by visual observation is affected by personal skill, this method has been standardized and improved by introduction of portable apparatus like SPAD meter (leaf color/ chlorophyll meter) for recording more accurate reading of leaf color intensity on the plants. SPAD meter reading has been successfully used in different countries for recommending N fertilizer to crops.
(3) However, one should not forget limitation of the second tool (leaf color chart or SPAD meter) for recommending fertilizers. This method is applicable only after the crop is grown up, not before sowing/planting of the crop. If your soil is deficient in nutrients, early growth of the crop will suffer- which can not be diagnosed by Leaf Color Chart or SPAD meter. Thus, soil test is the best method for recommending fertilizers to crops.
Thanks Dilip K. Kundu sir for your elaborate suggestion regarding fertilizer recommendation without soil test. However, your suggestion is concentrated within N recommendation mainly. What about other elements? According to A. Doberman (Ex. IRRI Soil Scientist) and R. J. Buresh (also IRRI Soil Scientist) omission plot technique can be used for calculating the respective nutrient requirement of specific crop in a specific field or soil.
LCC just measure the leaf color which varies with variety to variety. So, N management according to LCC is not justified.
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