A comparison of some chemical tests for available soil nitrogen

Summary The total nitrogen uptake of wheat in a pot experiment was found to be linearly related to the amounts of applied nitrogen in the range of 0 to 120 pounds N per acre. The N-value of the soil used in the pot experiment was estimated by extrapolation of the regression line of total nitrogen uptakevs rates of added nitrogen. The N-value was compared with the values of available soil nitrogen as estimated by three chemical methods, two of which used alkaline KMnO₄ and the third, dilute H₂SO₄ as hydrolysing agents of soil organic nitrogen. Results obtained by none of these methods agreed closely with the N-value. The amounts of nitrogen estimated by Shihata's method and Purvis and Leo's method were practically same and were appreciably lower than N-value whereas the value obtained by Subbiah and Asija's method was much higher than the N-value. However, Purvis and Leo's method deserves further study as it is well suited for mass-scale analysis.