Effects of water-potassium composite treatment on morphology and physiological indexes of cucumber seedlings grown on substrate in over-summer
Cucumber(Cucumis sativus L.)is one of the vegetable species with the largest planting area in facility agriculture,and it is also a vegetable crop that consumes a large amount of water.Worldwide drought is becoming more and more serious,and the lack of water prevents a large amount of fertiliser from being absorbed and used by the plants,and thus the plants will suffer from a variety of fertiliser deficiency symptoms.Reasonable water and fertiliser supply is required for high yield and high efficiency production of crops.In this experiment,we investigated the effects of three lower limits of irrigation(W60:60％ of the substrate field holding capacity;W70:70％of the substrate field holding capacity;W80:80％ of the substrate field holding capacity)and three potassium application rates(K0:0 mmol/L;K4:4 mmol/L;and K8:8 mmol/L)on the growth and development of cucumber planted in the greenhouse in the nutritive growth phase during the high temperature period in summer,including leaf photosynthetic characteristics,plant root indexes and plant biomass.The results showed that the W70K8 treatment improved the growth of cucumber.Significantly increases were found in plant height,stem thickness,number of leaves,internode length,leaf area growth indexes,and chlorophyll content of cucumber leaves,among which the contents of chlorophyll a,chlorophyll b reached the highest level.The net photosynthetic rate of cucumber leaves treated with W70K8 was the highest as 18.36 μmol/(m·s).The highest net photosynthetic rate 18.36 μmol/(m2·s)was observed in cucumber leaves,and the root vigour significantly increased to 88.24 pg TTF/(g·h).In conclusion,W70K8 treatment could improve the chlorophyll content,net photosynthetic rate,and growth indexes of cucumber during the nutritive growth period in substrate cultivation,to promote the growth and development of cucumber.The experiments showed that the appropriate water-potassium coupling mode for the nutritive growth period of cucumber cultivated on substrates in summer facilities is:70％of the field water holding capacity of the substrate with 8 mmol/L potassium.
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