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Abstract
The main objective of this research was to improve some fertility properties of calcareous soils having different content of calcium carbonate. Availability of P in such soils as well as P- Q/ I relationship parameters were evaluated under application of different composts via 2 sets of experiments. Used composts were prepared from several plant residues including: 1- compost of rice straw, 2- compost of banana leaves and 3- compost of mixed vegetable residues. Besides, the roles of biofertilizers such as Phosphorus Dissolving Bacteria (PBD) were also evaluated especially what concerns with altering measurements expressing P status in calcareous soils.
Different plant residues were composted in individual heaps after mixing with inorganic fertilizer activators to be then scattered over 1m2 area in successive layers. Each heap was slightly moistened to reach about 60% of its water holding capacity. Additional water was sprayed during the turning process to keep the moisture content. Representative samples from heaps were taken out after 1, 2, 4, 6, 8, 10 and 12 weeks to determination of EC and pH as well as contents of total organic C and some macro and micronutrients in the composted materials. To elucidate the roles of application of the indicated compost in activating P status in calcareous soils, two pot experiments were carried out. The first was conducted for calcareous soil containing about 31 % CaCO3. The soil was incubated with different rates of composted rice straw as individual or mixed with the other composts. Also, a bio-fertilizer (phosphorus dissolving bacteria, Bacillus Megatherium ) was added to the composts before incubation. Soil samples were taken within a short-term duration periods (2, 4, 8 and 24 hours) and long-term duration periods ( a week, two weeks, four weeks and eight weeks). The values of Olsen’s P were determined, as a measure for P availability. The obtained results indicated that increasing the application rate of rice straw compost led to significant increase in Olsen’s P in the soil inculcated.