Jamal H. Yaqoub*(1) andMohammed A. budalkareem(2)
(1). University Services Management Administration, University of Basrah, Iraq. (2). Department of Soil Sciences, Water Research, Faculty of Agriculture, University of Basrah, Iraq.
(*Corresponding author: Jamal H. Yaqoub E-Mail: jam13336@Gmail.com).
Received: 28/05/2020 Accepted: 13/06/2020
Abstract
An incubation experiment was laid out at Department of Soil Sciences and Water Resources, College of Agriculture, University of Basrah, Iraq, in 2019, to study the effect of humic substances (humic acid and fulvic acid) which extracted from different organic sources (rice straw, corn cobs, cattlle residue and poultry residue) composed aerobically for three months on phosphorus availability as related to calcium concentration in solution of two soils. Four levels of humic substances (0, 20, 40 and 60 L/ha) were applied to two soils along with 0, 50, 100 and 150 kg P2O5 /ha from either triple super phosphate or di-ammonium phosphate. Samples were incubated at 25 ± 2 °C for 14 days under field capacity moisture condition. Soluble calcium was determined and available P was determined after extracting by 0.5 M NaHCO3. In respect of soluble Ca, the result showed that increasing humic substances level decreased soluble Ca++ at both soils and both fertilizers used, with lowest values in the treatments of rice straw and poultry residue. Furthermore,TSP gave the highest values of soluble calcium as compared with DAP. Available P showed opposite trends as for available calcium. Available P values were differed with different humic substances treatment along with soils and fertilizer sources with the highest available P associated with treatments of rice straw at level of 40 L/ha for both soils.
Key words: Humic substances, Soluble calciumˏ Available Pˏ Ammonium diphosphateˏ Rice strawˏ Calcareous soils.