Composition of humic acids with respect to the degree of humification in cultivated soils with and without manure application as assessed by fractional precipitation

Figures & data

Table 1 Humic acid content in the soil and the degree of humification of humic acids†

Soil	Plot	Humic acid content (mg C g^−1)	A 600/C ^‡	log(A 400/A 600)^§
Togo	Initial	1.66	0.97	1.00
	TCF^¶	1.62	2.13	0.814
	TCM^††	4.30	1.55	0.971
Kuriyagawa	Initial	25.2	9.52	0.533
	KCF^¶	21.1	9.58	0.534
	K80M^††	25.1	8.93	0.540
	K160M^††	34.2	5.98	0.609
^†From Watanabe et al. (2007).
^‡Absorbance at 600 nm in 0.1 mol L^−1 NaOH per mg C mL^−1.
^§Logarithmic value of the ratio of absorbance at 400 nm to that at 600 nm in 0.1 mol L^−1 NaOH.
^¶Plot with chemical fertilizer.
^††Plot with manure at 40 (TCM), 80 (K80M) or 160 (K160M) Mg ha^−1 year^−1 plus chemical fertilizer.

Figure 1  Yield (□), A400/A600 (○) and A600/C (•) of fractions obtained from Togo humic acids by fractional precipitation in 0.01 mol L−1 NaOH–ethanol solutions. (a) Initial soil before the plots were initialised, (b) chemical fertilizer plot after 10 years and (c) plot with cattle manure at 40 Mg ha−1 year−1 plus chemical fertilizer after 10 years. Bars indicate ranges of duplicated data. A400/A600 and A600/C were not determined for 20P–40P.

Figure 2  Yield (□), A400/A600 (○) and A600/C (•) of fractions obtained from Kuriyagawa humic acids by fractional precipitation in 0.01 mol L−1 NaOH–ethanol solutions. (a) Initial soil before the plots were initialized, (b) chemical fertilizer plot after 19 years; (c) and (d) plots with cattle manure at 80 or 160 Mg ha−1 year−1 plus chemical fertilizer after 19 years. Bars indicate ranges of duplicated data. In (d) A400/A600 and A600/C were not determined for 20P.

Watanabe , A , Kawasaki , S , Kitamura , S and Yoshida , S . 2007 . Temporal changes of humic acids in cultivated soils with continuous manure application . Soil Sci. Plant Nutr , 53 : 535 – 544 .

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