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Nitrogen Mineralization from Humic Acid Fractions in Rice Soils Depends on Degree of Humification

^a B.V. Nguyen, Dep. of Crop Sciences, Can Tho Univ., Can Tho, Vietnam
^b USDA-ARS, National Soil Tilth Laboratory, 2150 Pammel Dr., Ames, IA 50011
^c Dep. of Agronomy and Horticulture, Univ. of Nebraska, Lincoln, NE 68583-0915

View larger version (22K): [in a new window]   Fig. 1. The correlation between the amount of N mineralized from the mobile humic acid (MHA) fraction or the calcium humate (CaHA) fraction that were extracted from seven tropical lowland rice soils and incubated in the IRRI soil versus Tanhoi soil under anaerobic conditions at 30°C for (a) 3 and (b) 6 wk. ** and *** indicate significance at 1 and 0.1% levels, respectively; ns is not significant.

View larger version (26K): [in a new window]   Fig. 2. The relationship between the amount of humic acid N mineralized and the amount of N contained in the humic acid fraction per kg extraction soil for the mobile humic acid (MHA) fraction and the calcium humate (CaHA) fraction that were extracted from seven tropical lowland rice soils and incubated in the (a) Tanhoi and (b) IRRI soils under anaerobic conditions at 30°C for 3 and 6 wk. * and ** indicate significance at 5 and 1% levels, respectively.

View larger version (26K): [in a new window]   Fig. 3. The relationship between the amount of humic acid (HA) N mineralized and the optical density at 465 nm for the mobile humic acid (MHA) fraction and the calcium humate (CaHA) fraction that were extracted from seven tropical lowland rice soils and incubated in the (a) Tanhoi and (b) IRRI soils under anaerobic conditions at 30°C for 3 and 6 wk. ** indicates significance at 1% level.