The effects of endosulfan and fertilizer source on soil fertility 2. Available soil nutrient levels and soil organic matter

Abstract A lab incubation study was conducted on three Quebec soils over 29 months. Soils amended with either inorganic or organic fertilizer (composted manure) were sprayed 0, 2, 4, 8 or 16 times per year with endosulfan as Thiodan (2.2 kg/ha). Application of the endosulfan affected extractable soil levels of Ca and P in two of the above soils, but the response was not linear. Soil levels of extractable K, Mg, Zn, Cu, Cl, B and SO4 and pH showed significant effects due to endosulfan treatment in one of the three soils used but organic carbon levels were not influenced by the insecticide at all. The source of fertilizer affected levels of P, K, Mg, Cu, Mn, SO4, Cl, pH and OC in at least two of the three soils. P, Mg, SO4 and pH increased in the composted manure (Organigro) amended soil; K, Cu, Mn and Cl were higher in the inorganically fertilized soil. A field study was carried out encompassing three cropping seasons. Three crops (potatoes, cabbage and strawberries) were grown on each of the three soils used in the incubation work. Plants were fertilized with either inorganic fertilizer or the composted manure and sprayed 0, 2 or 8 times per season with Thiodan at the equivalent of 2.2 kg/ha. The insecticide had no effect on the levels of any extractable soil nutrient, on organic carbon, or soil pH for any of the three soils sampled at the 1981 harvest of any of the three crops. There were some significant effects of fertilizer source on soil fertility. Extractable Ca and Mg were higher at harvest in the two mineral soils and Bray P was higher in three of the nine soil‐crop plots where Organigro was the fertilizer source. There was a limited effect of fertilizer source on organic carbon levels.