Study On Application Of Humic Acid In Plug Seedling Production Of Tomato And Cucumber

Although positive influences of humic acid on the growth of plants cultivated in hydroponic,soil pot or field conditions have been well established,its effects on growth and development of plants grown in plug seedling substrates have not received enough attention.In this study,we added humic acid before seed sowing and investigated the effects of humic acid application on growth,nitrate reductase activity,photosynthetic parameters and nutrition characteristics of tomato plug seedlings,and the effects of humic acid on the growth,osmotic adjustment and antioxidant enzyme activities of cucumber plug seedlings,which will provide a theoretical reference for the application of humic acid in plug seedling production.The main results are as follows:1.The plant height,stem diameter,ratio of root to shoot,root activity and health seedling index of tomato seedlings were significantly increased in a certain extent by the addition of humic acid,and the effects on the root were more significant than on the shoot.Adding 20 g·L-1 humic acid(T2)showed a distinct advantage in all the growth parameters,when the addition amount was larger(T4),it showed the worst performance.Adding proper amount of humic acid to the nursery substrates could significantly promote nitrate reductase activity,enhance the contents of photosynthetic pigment and net photosynthetic rate,advantageous to the plant photosynthesis,while superabundant humic acid addition decreased these parameters.Compared with CK,adding appropriate amount of humic acid decreased the Fo and NPQ,while increased the Fv/Fm and ?PS? content,which will conducive to the improvement of photosynthetic characteristics of tomato seedlings.The nitrogen,phosphorus and potassium contents of tomato seedlings were increased firstly and then decreased with the increase of humic acid content,the maximum value appeared under humic acid of 20 g·L-1.2.Compared with CK,the plant height,stem diameter,biomass were increased firstly and then decreased with the increase of humic acid content.The order of the seedling index in different treatments was T2>T1>T3>CK>T4,in which T2 significantly increased this parameter.The root length,root surface area,root volume and root diameter of cucumber seedlings treated with proper humic acid addition(16 g·L-1)were significantly higher than those of control and other treatments,and the root activity was higher than that of other treatments.Under the condition of wet substrate,compared with CK,the effect of humic acid on the rate of electrolyte leakage and MDA content of cucumber seedlings was not affected by the addition of humic acid,while under the condition of dry substrate,adding suitable amount of humic acid significantly decreased MDA content and electrolyte leakage rate,obvious increased the proline,soluble sugar and soluble protein content,improve the activity of antioxidant enzymes,indicating that addition appropriate humic acid could improve the resistance of cucumber seedlings to short periods of drought.