Assertion: cowpea's nitrogen | /r/HasProperty | determined using modified micro-kjeldahl method
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text: Total nitrogen was determined using the modified Micro-Kjeldahl method , phosphorus was determined colorimetrically at wavelength 660 nm using the vanadate molybdate method  and calculated using a standard curve of dihydrogen phosphate  Potassium concentration was determined using flame photometer (Atomic spectra AAS vario 6) .