OSMOTIC PRESSURE.
EFFECT ON GERMINATION.
Injury to germination of seeds or to seedlings caused by applications of fertiliser placed close to the seed.at; planting time has usually been attributed to excessive osmotic pressure of the soil solution. That, is, heavy applications of solultlo fertilisers were supposed so to increase the soluble salt content of the soil solution immediately around the seed or tliroots of the seedling that the movement of water into the seed or plant was inhibited, or even that water was withdrawn from tho plant cells. Research work by L. G. Willis and E. \. Davis, at tho North Carolina Agricullui"d Experiment Station, as reported :n Technical Bulletin 30, and published in the Fertiliser Review, indicates that interference with the water relationship of the seed or plant under these conditions probably has been over-emphasised. In a study to determine the toxicity to cotton seedlings of high concentrations of soluble nitrogonous fertilisers various nitrogenous materials, such as nitrate of" soda, sulphate of ammonia, leunasalpeter, calcium nitrate, and urea were used at various rates. It was found in the experiments that " the concentration of nitrogen necessary to cause injury is about the same whether this element is supplied in nitrate of soda, sulphate of ammonia, leunasalpeter, or calcium nitrate.. Eeavy applications of urea are somewhat more toxic than the other forms supplying tho same amounts of nitrogen." Tho osmotic pressure of the soil solution was found to be least with urea, which was tho most toxic material and greatest where nitrates were used. " There is nothing to indicate that injury is in any way associated with the osmotic pressure of the soil solution." ' , Another interesting finding was that tho rate of absorbtion of nitrogen in t e early growth of cotton was greatest w er urea was used and that nitrogen snpp in the form of ammonia, was tbsoibea more rapidly than when in t nitrates. A
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New Zealand Herald, Volume LXVI, Issue 20162, 24 January 1929, Page 5
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316OSMOTIC PRESSURE. New Zealand Herald, Volume LXVI, Issue 20162, 24 January 1929, Page 5
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