Responses in the growth of tick bean in the field to applications of superphosphate have been related to "available" phosphorus in irrigated alkaline soils. Tick bean is grou7n as a winter corer crop between vine rows in irrigation areas of the Murray Valley. Availability of soil phosphorus was assessed by its solubility either in carbonic acid or in a solution of sodium bicarbonate. The first reagent extracted phosphorus ranging from 0.7 to 24 p.p.m. of the surface 6 in. of soil sampled from the various test areas prior to the sowing of tick bean, while the second extracted 5-91 p.p.m. Both extraction methods gave similar relations between soluble phosphorus in the soil and the response in growth of tick bean to 2 cwt superphosphate per acre applied at sowing. Thus, considering the carbonic acid extract, the increase in fresh weight yield of green herbage of bean plant ranged from about 30 per cent. for soil initially at a level of 3 p.p.m. of soluble phosphorus to about 10 per cent. for soil initially at 10 p.p.m. These phosphorus levels correspond to about 20 and 46 p.p.m. as determined by the sodium bicarbonate extraction method.
