Studies Of The Mechanisms Of Improvement In The Growth Of Autumn Cucumbers And Soil Environment With Aerated Irrigation

This thesis presents findings from studies over two consecutive years of indoor experiments and analyses using autumn cucumbers with aerated irrigation (AI). It reveals the impact of AI on crop growth, the agronomic and physiological characteristics as well as the soil environment. It provides valuable information to guide further research and extension of findings from similar AI techniques. The studies employed 3 treatments on autumn cucumbers, and were based on two consecutive years of pot experiments in a greenhouse: Treatment one (T1)-aerated irrigation three times in the morning, at noon and in the evening; Treatment two (T2)-aerated irrigation in the morning only, and the control (CK) with regulated irrigation. All the experiments had regulated deficit irrigation, routine fertilizer applications. The main findings are as follows.(1) Compared to CK, T1 and T2 have generated different effects on the agronomic characteristics of stems and leaves. The germination rates of T1, T2 are 27.50% and 26.25% higher than the CK, respectively; the germination potential is 10.18% and 9.72% higher than that of CK, respectively; the germination ratio increased by 9.72% and 4.16%, respectively; the germination index increased by 18.15% and 14.18%, respectively; the vigor index increased by 27.73% and 22.06%, respectively; the germination uniformity increased by 36.04% and 3.55%, respectively, and the seedling index increased by 13.82% and 25.56%, respectively. During the germination stage, the order of responses of the agronomic characteristics of the roots to AI is CK>T2> T1 except for the root length which is T2>CK>T1). From the seedling stage to the cucumber formation, the order of the responses to AI is T1>T2>CK. From germination to seedlings, the differentiation of stems and leaves is not obvious. From the early flowering stage to cucumber formation, the order of the responses of stems and leaves to AI is T1>T2>CK. At the end of cucumber growth, compared to CK, the yield per cucumber increased by 56.09% for T1 and 24.19% for T2, respectively; the dried fresh biomass increased by 57.27% for T1 and 22.26% for T2, respectively, which represent the dry matter increase by 80.84% for T1 and 51.58% for T2, respectively, and the dry-fresh matter ratio of 34.66% for T1 and 24.19% for T2, respectively. In the fruit quality:the soluble sugar、soluble protein、vitamin C、free amino acid contents are all improved with the order of T1>T2>CK; the comparative order of nitrate contents is CK>T2>T1.These results show that with AI the oxygen concentration in the root zone is increased which is beneficial to germination, seedling uniformity, promoting seedling and root growth. From the early flowering stage to cucumber formation, increased oxygen in the soil is highly beneficial to cucumbers’growth, cucumber formation, weight increase, and the increase in the biomass. The increase in the dry matter in the roots, stems, leaves and cucumbers eventually lead to the increase in the yield. These benefits are more obviously when AI is practised frequently. The overall analysis of the findings shows that the best AI combinations for growing cucumbers are, respectively, T2 for the germination stage and T1 for the seedling, early flowering and cucumber growth stages.(2) Compared to CK, the treatments T 1 and T2 both have significant effects on plant physiological indexes during different stages. The leaf SPAD content, photosynthesis rate, and the root activity follow the order of T1>T2>CK. At the end of cucumber growth, the following results have been derived:In the roots:the catalase activity, abscisic acid (ABA) content, the soluble protein are all improved with the order of T1>T2>CK; the comparative order of soluble sugar contents is CK>T2>T1; In the stems:the soluble protein content and the catalase activity follow the order of CK>T2>T1 while the soluble sugar content has the order of T1>T2>CK; In the leaves:the soluble sugar and soluble protein contents as well as the catalase activity have the order of T2>T1> CK while for the ABA content it is CK >T2>T1.These results indicate that from the seedling stage onwards the increased oxygen supply to the tillage layer in the soil can improve the root vigor, increase the contents of soluble protein and soluble sugar and chlorophyll concentration, and improve plants’activity to remove superoxide free radicals, metabolic activity leading to an improved cucumber quality. Meanwhile, AI also shows apparent benefits in prolonging roots’activity and delaying the crops’ageing process, which are more obvious when AI is practiced more frequently.Correlation analysis shows that A better positive relationship exists between the plant physiological characteristic indexes and AI in a greenhouse at the later stage of cucumber growth; There appears significant positive correlations between the catalase, soluble protein, ABA and the activity of the root system, and between the leaf photosynthesis rate and the chlorophyll concentration and the soluble sugar; There exists significant negative correlation between the soluble sugar, catalase and ABA contents in roots and the root vigor, and also between the ABA and soluble sugar contents, chlorophyll concentration, and photosynthesis rate.The path analysis shows that with AI the catalase (X1) in the roots has the maximum effect on the root activity (Y), and together with the soluble protein (X3), and ABA (X4) it determines the positive effect on the root activity while the soluble sugar has the largest negative effect on the root activity. The regression equation for this relationship is Y= 2333.66+61.09X1+43.33X2-2560.03X3. The soluble sugar (X1), ABA (X2) and chlorophyll concentration (X3) in leaves to some extent restrict the photosynthesis rate. Soluble sugar and ABA have a decisive negative effect on the photosynthesis rate (Y), which is quantified using the regression equation Y=-6.410.79X1-0.17X2+0.35X3.(3) Compared to CK, treatments T1 and T2 have significant effects on the number and variability of soil bacteria, fungi, actinomycetes, soil microbial biomass, and the carbon/nitrogen (C/N) ratio in the root zone at different stages of the cucumber growth in the greenhouse. The sucrose enzyme and cellulase performance follow the order T1>CK>T2 while other indexes have the order of T1>T2>CK. These results show that AI of cucumbers in the greenhouse has a promoting effect on the number of soil microorganism, the accumulation of microbial biomass, carbon and nitrogen contents and enhancing the soil enzyme activity, and these results are obvious with multiple aeration. Comparative studies of the AI effects on fertilizer efficiency show that from the seedling stage to cucumber formation in the root zone there are:A gradual reduction in the alkali hydrolyzable nitrogen content; Small fluctuations of available phosphorus content; A decrease in the total phosphorus content, and small fluctuations of total potassium and organic matter contents. The above findings indicate that AI is beneficial for the crops to take up alkali hydrolyzable nitrogen, available phosphorus and potassium as well as the decomposition of organis matter in the soil.(4) Compared to CK, treatments T1 and T2 have significant effects on cucumbers growing in the greenhouse in terms of yield, and water and fertilizer use efficiencies:The comparative results in terms of yield and three types of fertilizers have the orders of T1>T2>CK, While on the microscopic level of leaves, the order of AI effects is T1>T2>CK for the seedling and cucumber formation stages, and T1>CK>T2 for the early flowering stage, and the comparative results in terms of AI treatments on water use efficiency shows that water consumption with the T1 is slightly better than CK by 3.74%, and that T2 consumed 98.93% of water used under CK, respectively. These results are a consequence of an increased yield, which can be expressed as a regression equation Y=4833.9x-731.74x2-3157.2, where Y is the water consumption in ml and x is time in days.