A calcareous soil incubation experiment for four tasting of 16 weeks was
carried out to ascertain the effect of compost, olive waste and lemon waste, on the amounts of
extractable iron, manganese, copper and zinc in a calcareous soil. The rates of organic materials
added were 0, 0.5, 1.0, 1.5 and 2 % of the air-dried soil on dry weigh. The periods of sampling
affected soil pH and were the lowest (pH = 7.32) was produced at the fourth time of sampling with
olive waste. Decreasing pH values with increasing rate of applied organic waste were observed
at each time of sampling and with increasing time of sampling. The compost gave the highest
values of available Fe, Mn and Zn at the fourth time of incubation (5.41, 22.04 and 5.02 mg/kg
soil, respectively), while, the olive waste gave the highest value of available Cu (5.11 mg/kg soil)
at the fourth time of incubation. Generally, the available Fe, Cu, Mn and Zn were increased with
increasing organic materials rate and increasing time of sampling. The highest values of available
Fe (6.16 mg/kg soil), available Zn (6.21 mg/kg soil), available Mn (23.87 mg/kg soil) and available
Cu (6.71 mg/kg soil) were recorded for 2% organic material application, rate at the fourth time of
sampling.