We recently proposed a simple method for estimating total nitrogen content in paddy soil. In this method, soil is extracted with a commercial 3% hydrogen peroxide (H2O2) solution at 25 ◦C for 40 h, and electrical conductivity (EC (H2O2)) of the extract is measured. This study aimed to further evaluate the method’s applicability to soil samples collected at the farm scale by using the original and six additional H2O2 solutions that are locally and commercially available. The results obtained with the original solution indicated that the determination coefficients between EC (H2O2) and total N were statistically significant at all farms examined: Moka, 0.78 (n = 13); Kyoto, 0.50 (n = 16); Kizu, 0.43 (n = 89); and Kawatabi, 0.25 (n = 18). The EC of the tested H2O2 solutions varied from less than 0.05 to 1.4 mS cm−1 because of the addition of different stabilizers. EC (H2O2) values obtained with the less stabilized H2O2 solutions (one from Japan, one from USA, and the analytical grade 6% solution) agreed well with those obtained with the original solution. Thus, the proposed method can be useful for estimating the farm-scale variation in soil total N, provided a H2O2 solution with a low EC (<0.2 mS cm−1) is used for the extraction.
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