Pot experiment was carried out to study the effect of water - potassium coupling on photosynthetic characteristics and water use efficiency of soybean. In this experiment, five water supply levels and three potassium fertilizer levels were applied at seedling stage, flowering stage and podding stage respectively. The results showed that both soil water and water - potassium coupling had highly significant effects on soybean net photosynthetic rate (Pn) when soil water content was controlled at seedling stage and flowering stage. The soil moisture had positive effect on Pn when soil moisture was regulated at podding stage. The measured Pn after flowering stage or podding stage was superior to that of seedling stage for the same treatment. Photosynthesis rate( Pn) , transpiration rate( Tr) and stomatal conductance ( Gs ) had similar changes at the same stage where soil water content played a more important role than potassium fertilizer. In generally, the same fertilizer condition, the impact of soil moisture level on Pn, Tr and Gs was ranked as W4＞W3, W5＞W2＞ Wl. The potassium fertilizer application ( K2 and K3 ) enhanced Pn, Tr and Gs in soybean only with suitable soil moisture condition (W3). Soil water content had a positive effect on water use efficiency (WUE) and played a more important role than potassium fertilizer when soil moisture was controlled at the same growth stage. When soil moisture was controlled at seedling stage and flowering stage, net photosynthetic rate was highly significantly relevant to root, stem and leaf dry matter weight(p＜0. 01). The correlative degree between net photosynthetic rate and the dry matter weight of each apparatus showed the order of stem > leaf > root. When soil moisture was controlled at podding stage, net photosynthetic rate had highly significantly related to root, stem and leaf dry matter weight(p＜0. 01) and significantly correlated with pod - seed dry matter weight(p＜0.05).%盆栽条件下,研究了不同生育时期水钾耦合对大豆光合特性及水分利用效率的影响,并对光合速率与各器官干物重进行相关分析.结果表明:苗期与花期控水时,土壤水分及水钾互作极显著影响净光合速率(Pn)；结荚期控水时,水分极显著影响Pn.花期与荚期控水后测定的Pn要高于苗期的Pn.水钾耦合对光合速率(Pn)、蒸腾速率(Tr)和气孔导度(Gs)的影响趋势相似,即水分效应要优于钾肥,且一般而言同一钾肥水平下,土壤水分的影响表现为:充足W4＞适宜W3、特涝W5＞略旱W2＞特旱W1.只有当土壤水分供应适宜(W3)时,钾肥的施用提高了植株的Pn、Tr和Gs.水分对植株水分利用效率(WUE)的影响要优于钾肥,且水分为正效应.苗期及开花期控水条件下,檀株的Pn与根、茎、叶干物重呈极显著正相关(p＜0.01),且Pn与各器官的相关程度表现为茎＞叶＞根；结荚期植株Pn与根、茎、叶干物重仍呈极显著正相关(p＜0.01),与荚粒干物重呈显著正相关(p＜0.05).
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