Microbial and earthworm populations and some soil chemical characteristics were measured in soil samples collected from an existing fertilizer trial that had been in progress for 3 years. The samples were collected two weeks before and two weeks after the annual applications of single superphosphate (SSP) or North Carolina phosphate rock (NCPR). There were no significant long-term fertilizer effects on any of the characteristics measured but there were some significant changes between the two samplings. Total bacterial count (69 x 106 to 6 x 106 g-1 soil) and the fungal count (l3 x 105to 5.2 x 105 g-1 of soil) declined significantly in all treatments between the two samplings. This decline was significantly smaller for fungi in fertilized plots. There were significant increases in populations of gram negative bacteria (28 x 105 to 52 x 105 bacteria g-1 of soil) and phosphate rock (PR) dissolving bacteria (7 6 x 105 to l3 x 105 bacteria g-1 of soil) two weeks after fertilizer application. Populations of these bacteria did not change significantly in unfertilized plots. The water-extractable carbon declined significantly in unfertilized and SSP-treated plots but not in NCPR-treated plots. The levels of ammonium oxidizing bacteria, PR-dissolving fungi, fluorescent Pseudomonas spp. and microbial P were unaffected by fertilizer. Two groups of earthworms were examined once before the fertilizer application. There were no significant fertilizer effects on adult or juvenile populations of Lumbricus rubellus or Aporrectodea caliginosa.
SUMMARYThe extent to which light, potassium, and form of nitrogen (ammonium and nitrate-nitrogen) modified the requirement by kiwifruit (Actinidia deliciosa var. dcliciosa) for chlorine was examined in solution culture. A greater concentration of chloride was required in the nutrient solution for maximum growth under low irradiance than under high irradiance. In the absence of chloride, growth was severely restricted and the response to potassium was significantly reduced, especially under low light.Greater concentrations of chloride accumulated in the leaves of plants grown under high irradiance than under low irradiance. Increasing the concentration of nitrate in tbe leaves either by growing the plants under low light or by increasing the quantity of nitrate in the nutrient solution, substantially reduced tbe accumulation of chloride. The decrease in the concentration of chloride was accompanied by an increase in the concentration of nitrate. Thus the combined concentration of nitrate and chloride was relatively constant over a wide range of treatments suggesting that a negative feedback mecbanism may be operating in this species. However, while nitrate was preferentially accumulated by kiwifruit plants it could not substitute fully for chloride. Once the concentration of chloride in the leaves was decreased below 70//mol g ' d. wt by competing nitrate ions, growth was substantially reduced. It is concluded that the effect of light on the chloride status of kiwifruit plants can largely be explained in terms of the strong competitive effect from nitrate ions, witb greater concentrations of nitrate accumulating in rhe leaves under low irradiance than under high irradiance.Tbe negative effect of potassium on the chloride status of the plants is not considered to be a specific physiological effect but rather the consequence of chloride, along with other non-limiting nutrients, accumulating in the tissues of the severely potassium deficient plants.The ecological implications of the results are discussed in relation to features of the habitat in China where kiwifruit vines have evolved. The results of tbe present study are entirely consistent with this species having evolved in an environment where tbe availability of cbloride and ammonium is relatively high while that of nitrate is severely restricted. It is concluded that the high concentration of chloride required in the tissues of kiwifruit vines is an adaptation which minimizes the expenditure of energy on the generation of osmotic pressure in the tissues rather than specifically maintaining charge balance.
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