Two field experiments were carried out at saxna Agric Res. Station In 2004
and 2005 seasons to study the effect of different soil moisture depletion, 35, SO and
65% and potassium fertilizer levels; untreated 24 and 48 kg K201fed. on soybean
yield, some water relations and N, P, K concentrations of seeds. The obtained results revealed that the Irrigation at 50% soil rnorsture
depletion surpassed the other two depletions (35 and 65%) in increasing the seed
yield of soybean by 6.37 and 14.29% in the 1.¹ season and 9.09 and 16.59 in the 2^nd
season. Application of 48, kg K20lfed. increased seed yield by 21.53 and 13.23%
than application of 0.0 and 24 kg K20lfed. in the 1" season. While, in the 2^nd season
the seed yield increased by 21.43 and 10.36%. The greatest amounts of water consumptive use were found to be 2007 43
and 1981 83 mJ/fed in the ," and 2^nd seasons respectively under 35% depletion The most suitable water applied throughout the two seasons are 2646 4 and
24907 mJ/fed in the 1" and 2M seasons under irrigation 50% depletion of available
soil moisture which produced the greatest seed Yield. The highest values of crop water use and field water use efficiencies were
achieved from interaction between irrigation at 50% depletion of available soil
moisture and application of 48 kg K20lfed. in both seasons.