Diagnosing P deficiency in black gram (Vigna mungo (L.) Hepper) by plant analysis and soil testing: Diagnostic norms.
1993
Rashid A. | Din J.
The minimum P concentration in diagnostic plant parts associated with optimum plant growth is called 'internal P requirement' or 'critical P concentration'. A pot culture experiment, using P-deficient soil of Missa series (Typic Ustochrept), was carried out to determine the internal P requirement of black gram or 'mash' (Vigna mungo (L.) Hepper). Phosphorus fertilization enhanced crop growth; the maximum increase in grain yield was 373 % over the control. Near-maximum grain yield of black gram was associated with 28 mg fertilizer P/kg soil. Critical P concentration was 0.37 % in whole shoots and 0.28 % in most recently matured leaves. Phosphorus content in mature seeds of black gram was a good indicator of the P fertility of the soil; the critical P concentration in mature seeds was 0.35 %. Phosphorus extracted by three soil tests correlated well with each other and the P contents of diagnostic plant parts. Critical soil test P levels for pot-grown black gram were 8 mg P/kg soil; 6.5 mg P/kg soil; and 23 mg P/dm soil. As the 'universal' soil tests (AB-DTPA and Mehlich 3) are inexpensive, easier, and less time-consuming than the NaHCO3 test now used routinely in many countries, they could be used for rapid site and crop-specific fertilizer recommendations.
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