Abstract
Understanding the role of humic substances in soils is important for developing and utilizing organic fertilizers or soil amendments for sustainable agriculture. The objective of this study was to determine the effects of different fractions of humic acids derived from Leonardite on enzymatic activities and bioavailability of nutrients in a soil. The experiment was carried out by mixing different factions of humic acids with a soil and incubated for 70 d. The treatments included five factions of humic acids (HS1 (low molecular weight), HS2 (medium molecular weight), HS3 (large molecular weight, SED (sediment of fractions), HS (mixture of HS1, HS2, and HS3)), raw Leonardite (IM) and a control (no addition of humic acid). Experimental results showed that application of humic acids significantly improved acid and alkaline phosphatase activities, especially with HS1. Humic substances with high molecular weights significantly inhibit urease activity, and the optimal application rate was 600 kg/hm2 of humic substances with the high molecular weights. Concentrations of NH4+-N were decreased with increasing humus applications. All treatments (HSmix, HS1, HS2, HS3, IM, SED) did not affect the soil contents of Ca, although soil concentrations of K, P, Cu, Zn were increase significantly when small molecular weight humus (HS1) was applied. Keywords: humic acid, molecular weight, Leonardite, enzyme, nutrient content DOI: 10.25165/j.ijabe.20201303. Citation: Sun Q, Liu J L, Huo L F, Li Y C, Li X, Xia L R, et al. Humic acids derived from Leonardite to improve enzymatic activities and bioavailability of nutrients in a calcareous soil. Int J Agric & Biol Eng, 2020; 13(3): 200–205.
Highlights
It has been long reported for the effects of soil organic matters on plant growth and nutrient uptake[1,2,3,4]
Humic acids are very important for enzyme functions because they compose a large proportion of soil organic matter and may help to stabilize or inhibit enzymatic activities[27]
The same trend occurred during the HS1 treatment, when the phosphatase activity peaked (75.6 mg/kg·h), declined with increasing application rates
Summary
It has been long reported for the effects of soil organic matters on plant growth and nutrient uptake[1,2,3,4]. Even though humic acids extracted from soils under widely different pedologic (sandy, loamy or clay soils) and geographic environments had similar analytical characteristics and chemical structures, the fractions with large molecular weights showed the greater effects on enzymatic activity in soils than fractions with low molecular weights[8,9,10,11,12]. This suggested that the sizes of molecular weights were of the importance in determining the magnitude of effects on soil enzyme activity. The results will provide valuable information for using the Leonardite to improve soils
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
