| Based on the background of greenhouse vegetables with high-frequency irrigation and transplanted seedlings cultivation and taken the root-soil-water system as the core in this paper. Seven field experiments were conducted for solving the problems of serious seepage in field irrigation water, the lack of water-saving irrigation mechanism and the unsoundness of irrigation indicator system.The relations of root-soil-water-fertilizer under the high-frequency irrigation in greenhouse environment shallow-root vegetable were studied in this paper. A series of results were output, they are following: The mechanism of vegetable leakage control irrigation was clarified. The new concept of"root, water and fertilizer synchronous management"was put forward to. The management strategy of"determining water supply by root distribution"was adopted. The key indexes of root irrigation were confirmed and the water-saving purpose by leakage control irrigation was achieved. That all put forward the effective way of achieving the target of"evaporation reduction and leakage control"to use water effectively on vegetables. The main research results are as follows:1. Response of the root distribution characteristics with soil moisture environment and its effects with irrigation methods on greenhouse vegetablesBy studying the response characteristics of the vertical distribution of greenhouse tomato, cucumber and cabbage on different irrigation method, soil moisture, water-supply interface, covering condition and other factors and taking the soil layer with 90% of root mass as the main root layer and the soil layer with greatest root mass as the root-concentrated layer of vegetable, it can obtain that:1.1 The distribution of main root layer of vegetables is relatively stable. Its space distribution and displacement characteristics in soil are mainly affected by vegetable-bearing period and water supply point and other factors have fewer effects on them; it mainly distributes in the 0-30cm shallow soil layer and becomes deep gradually according to the bearing process; the vertical distributions of different vegetables in soil layer are: over 91% of cabbages in the 0-10cm soil layer, over 99% of greenhouse cucumbers in the 0-25cm soil layer, and over 92% of greenhouse tomatoes in the 0-30cm soil layer."Managing according to shallow root"is particularly important for vegetable crops.1.2 The depth of vegetable root is almost not affected by the changes of irrigation method, irrigation quantity and soil moisture environment, and it is also stable. The largest vertical depth of greenhouse tomato is 60cm, the largest vertical depth of greenhouse cucumber is 30cm, and the largest vertical depth of greenhouse cabbage is 30cm. It shall pay more attention to the root horizontal control for vegetable production management.1.3 The vertical distribution of vegetable root-concentrated layer is changeable. The root-concentrated layer is markedly affected by irrigation method, soil moisture, water-supply interface, covering condition and other factors. Drip irrigation, laminating and high moisture all can make it shallow. By underground water supply (infiltration irrigation), the root can be better distributed than by aground water supply (furrow irrigation). Adjusting the distribution scope of root-concentrated layer, it can make the root absorb moisture and nutriment in larger scope.2. Soil water consumption characteristics of tomatoes under different irrigation methodsBy studying the change characteristics of tomato root soil space on soil water consumption layer, soil moisture scope, quantity and ratio in bearing period and under different irrigation method, it can obtain the following results:2.1 The main water consumption layer of vegetable is stable. The irrigation method can affect the largest water consumption layer, soil moisture active layer, sub-active layer, stable layer, main water consumption layer and other water consumption characterizations of tomato field in different bearing period. However, for the tomato field in bearing period and irrigated by any way, soil moisture active layer is in the 0-30cm soil layer; stable layer is in the 30-60cm or 40-60cm soil layer; main water consumption layer is in the 0-40cm soil layer. The water consumption of this layer accounts for over 85% to 90% of the water consumption in tomato root layer; in the harvest, the layer with largest water consumption is in the 0-10cm soil layer, and it is in the 10-20cm soil layer in other different period and under each irrigation method; the 0-40cm layer is the key root-soil layer which shall be considered in leakage control irrigation of vegetable field.2.2 The daily water consumption of vegetable is changeable. Under different irrigation method and in different bearing period, the water consumption of tomato orderly reduces from full fruiting period, later fruiting period to flowering and fruiting period. The daily water consumption for under-membrane infiltration irrigation is 0.77mm in flowering and fruiting period, 2.02mm in full fruiting period and 1.95mm in later fruiting period; the water consumption for under-membrane furrow irrigation is 0.74mm in flowering and fruiting period, 1.90mm in full fruiting period and 1.99mm in later fruiting period; the water consumption for furrow irrigation is 1.22mm in flowering and fruiting period, 3.32mm in full fruiting period and 3.29mm in later fruiting period. It provides a basis for tomato field in making changeable irrigation period.3. Contribution rate of different root-soil space on the growth stages of tomatoesBy the manual-controlled root-soil distribution test for gauze interlayer and plastic cloth interlayer, it studies the contribution rate of different root-soil space on the growth of greenhouse tomatoes and shows that:3.1 The root-soil space of different growing characters is different. For the plant height, it needs 10cm root-soil space in first flowering period and 30cm root-soil space in flowering and fruiting period to satisfy the water and fertilizer supply in the same compared condition; for the leaf number, stem diameter, inter-node and other growing characters, it only need 10cm root-soil space in different periods; for the leaf area, it needs 10cm root-soil space in first flowering period and later fruit expansion period and 20cm root-soil space in first fruit expansion period; for the output, it shall have 30cm vertical root-soil space at least to make tomato achieve the output which has unobvious difference with the comparison. 30cm root-soil space can make the tomato output reach 97.9% of the comparison and 40cm root-soil space can make the tomato output reach 99.1% of the comparison. The interlayer limits the supply and demand of root, soil, water and fertilizer. Only the root-soil space over 40cm can fully satisfy the water consumption demand of tomato. And the plastic cloth interlayer with suitable depth is good for the growth and output of tomato.3.2 The plastic interlayer with different depth and the output of tomato are in the conic relation. The best scope is in the 40cm soil-root layer, and the largest"root-soil functional space"of tomato field is 0-40cm. Thus, as long as the root, water and fertilizer are in the same position in soil-root space, it can achieve a high output and water-fertilizer use efficiency. So the root-soil layer management and control can make vegetable achieve the objects of water saving, high efficiency and high output. Meanwhile, it proves that it is unsuitable to use"moisture-storing irrigation"for shallow-root vegetables.3.3 The root biomass and tomato output are in the conic relation. The soil interlayer limits the vertical distribution scope of root; however, it can obtain high output if having a certain degree of root biomass and the tomato root also has"redundancy"phenomenon4. Confirmation for the water ration index of leakage-control irrigation on vegetables4.1 Response of cucumber growth character on soil moisture and threshold of irrigationWhen the monitoring layer of irrigation water is in the 0-40cm layer, it studies the water content bound of soil and the most suitable soil moisture for cucumber in different bearing periods, and the result shows that:4.1.1 The increment speed of each cucumber growing index is different in each growing period. For different objects, the effect is most obvious if controlling and adjusting it in the key period with fastest increment speed; meanwhile, it doesn't have obvious effects on the growth of cucumber if properly reducing the resource input in the period with minimum increment speed. The plant height increases fastest in the seedling stage, while leaf number increases fastest in the first fruiting period, leaf area increases fastest in the full fruiting period and stem diameter increases fastest in the later fruiting period; in the later fruiting period, the increment speed of plant height, leaf area and leaf number is minimum.4.1.2 According to the effects of soil moisture treatment on output, it confirms that the soil moisture lower bounds of cucumber in different bearing periods are respectively: 75% in seedling stage, 75% in first fruiting period, 85% in full fruiting period and 85% in later fruiting period; the upper bounds are respectively: 95% in seedling stage, 95% in first fruiting period, 100% in full fruiting period and 100% in later fruiting period; the suitable soil moisture indexes in different periods are respectively: 75-80% in seedling stage, 75-95% in first fruiting period, 85-95% in full fruiting period and 85-95% in later fruiting period.4.1.3 According to the suitable soil moisture threshold of cucumber and the equation of economic irrigation amount, it estimates that the range of economic leakage-control irrigation amount for cucumber in different bearing period is 10 to 14 m3/667m2. 4.2 Reaction of Tomato Growth & Development Character to Irrigation Amount It is the study of influence by different irrigation amounts on tomato's growth, development, yield and water use efficiency according to method of furrow irrigation under complete coverage film. The result shows:4.2.1 Different growth and development characters have different stages for reaction on treatment of irrigation amount. Plant height, Fv/Fm and photosynthetic rate can show the limit effect of water shortage at the stage of relatively large water demand of tomato; whereas fluorescence reaction is occurred upon harvest time. Growth rate of number of leaves presents limit effect of water shortage only from the fifth inflorescence fruited and to the primary stage of pinching.4.2.2 Different growth and development characters have sensitivity to difference for reaction on treatment of irrigation amount. Growth rate of stem diameter basically is not affected by treatment of irrigation amount and sensitivity of influence of number of leaves is appeared in a very short primary stage. Reflection of Plant height on water treatment presents in all time period. Fv/Fm and photosynthetic rate only shows difference at the pre-stage of harvest or upon entering harvest time. Yield and water production efficiency are the final presence of water treatment. It is a conic relationship between water consumption by different treatment and yield and water production efficiency.4.2.3 Integrating growth, yield and water production efficiency index, combining estimated result of the water production function as well as considering water-saving and water production efficiency as the main proof, it is proper to use irrigation amount of 15m3/667m2 for tomato production in autumn and winter. It is not prominent in yield difference between 10 and 15m3/667m2 by irrigation. Irrigation amount with 10m3/667m2 can be also considered as production selection.4.3 Soil Migration Principle & Irrigation Leakage Control Quota of Tomato Field Water and Nutrient under Different Irrigation Quotas4.3.1 Under conditions of irrigation without fertilization and with fertilization, irrigation quota, soil nitrate nitrogen leaching amount, leaching ratio, storage rate and leakage rate all present linear relationship; irrigation will cause nitrate nitrogen leaching at the shallow root layer(0-20cm) and under conditions of irrigation with fertilization, there is a peak for nitrate nitrogen by irrigation quota range from 7.5mm to 15 mm but two peaks from 22.5mm to 45mm; considering 40cm root-soil interface as discriminated interface, irrigation quota ranging from 7.5mm to 15mm and under conditions of irrigation without fertilization, the root-layer soil nitrate nitrogen leaching rate is 0, which ranges from 0 to 5.19 percent under conditions of irrigation with fertilization; irrigation quota ranging from 22.5mm to 45mm and under conditions of irrigation without fertilization, the root-layer soil nitrate nitrogen leaching rate is from 5.38 percent to 19.08 percent, which ranges from 21.91 percent to 61.96 percent under conditions of irrigation with fertilization; furrow irrigation under tomato film in greenhouse can reduce fertilization leaching and leaking water-saving and irrigation quota into 15mm.4.3.2 If irrigation quota is higher than the level of 30mm, water penetration depth can reach the soil layer by 120cm; if irrigation quota is lower than 15mm, it can reach 60cm to the maximum depth. Moreover, it can only reach 40cm for water penetration depth with irrigation quota of 7.5mm, but partial layers can not reach 85 percent of field water holding capacity; bounded by 40cm main root layer, it will cause leakage above 59.13 percent for irrigation water with irrigation quota for more than 30mm; bounded by deepest root layer, namely the flowering fruit bearing stage will cause leakage above 48.23 percent for irrigation water and the full fruit bearing stage will cause 36.27 percent leakage for irrigation water. If irrigation quota is lower than level of 15mm, it will not cause leakage of irrigation water; within irrigation quota range of 7.5mm-45mm, leakage rate beyond irrigation root layer presents the linear correlation with irrigation quota; irrigation quotas with 0 leakage rate at different soil layers by 0-40 cm, 0-50 cm and 0-60 cm are 9.55mm, 11.27mm and 12.07mm respectively.4.3.3 The proper irrigation quota is from 15mm to 22.5mm for effective water supplier and water-nitrogen leakage control in tomato flowering fruit period and harvest time with the core of root-water-soil coupling; it is (0, 22.5mm) for the threshold value of controlling leakage outside the water-nitrogen root. 4.4 Integrating above-mentioned biological response for vegetable by water treatment and characteristics of water and soil engineering, the leakage control economical irrigation amount range is 10-14m3/667m2 according to different growth periods of cucumber and it is the suitable irrigation quota 10-15 m3/667m2 for tomato. The threshold value range of irrigation amount is (0, 22.5mm) for controlling leakage outside the water-nitrogen root of tomato. The irrigation water quota of leakage control is determined to be (0, 22.5mm) according to the basic moisture of irrigation for detail. But the largest irrigation quota edge of leakage control is 22.5mm.5. The effective of integrated techniques on the output of greenhouse vegetablesAccording to tomato planting experiment in greenhouse and with comparison of soil water consumption characteristics, water-saving effect and other comprehensive effect among three irrigation methods including furrow irrigation, furrow irrigation under complete coverage film and new infiltration irrigation, the result indicates:By using method of irrigation under film, it can reduce consumption of irrigation and infiltration under film and furrow irrigation under film can increase irrigation efficiency by 47.98 percent-48.90 percent;it also can increase water production efficiency by 43.80 percent-91.57 percent. Irrigation under film can obviously reduce relative air humidity in greenhouse, effectively decrease possibility of occurring damage by diseases and insects and enhance vegetable quality.In conclusion, this study, according to relationship research on vegetable field root-soil-water-crop, discovers that vegetable in greenhouse has following obvious features:⑴Three relative stability, namely it is relatively stable for vegetable to soil water consumption of 0-40cm root-soil layer and root main distribution layer 0-30cm and root maximum depth are relatively stable.⑵Correlation. There is a prominent correlation feature between root spatial distribution and root-soil functional and spatial layout. Namely, main spatial distribution of vegetable root lies in 0-30cm and the spatial layout of root main function lies in 0-40cm.⑶Controllability. Irrigation amount and water, N infiltration amount and leakage amount have controllable boundary feature. Namely, the irrigation quota of controlling leakage outside the water-nitrogen root layer is from 0mm to 22.5mm with maximum threshold value of 22.5mm.⑷Sensitivity to differences. Namely the response of vegetable growth and development on water not only has sensitivity to differences not only during growth and development stage, but also among different characters at the same time.The study result has obvious difference by comparing to outdoor vegetables and field crops regarding to soil root-growing space, crop sensitivity and controllable boundary range. This difference is the biological, ecological and water and soil engineering basics of vegetable irrigation leakage control, which has revealed the basic mechanism of vegetable irrigation leakage control, namely Water Determination Based on Root aiming at shallow root vegetables and crops, realizing water-saving for irrigation leakage control by reaching operation of Root-Water-Fertilizer Collocated. It is the effective way to use water in high efficiency for vegetables by integrating current reduced pressure distillation technology which can realize Reduced Pressure Distillation and Leakage Control for vegetables.The result of this study uses the method of field measuring which makes up for limitation brought by application and production of pot experiment result. It selects three elements including crops-soil-water and confirms policies and key technology index for water-saving irrigation by comprehensive reflection. Moreover, the result achieved can precisely reflect essence of field soil-water-root. It not only provides basics and materials in terms of biology, ecology, water and soil engineering and cultivation science for water-saving study and practice of protected vegetable, but also provides experience for water-saving study and practice of other shallow root crops, which has the important theoretical and practical application value.Aiming at vegetable irrigation cycle variability and water demand stage features, it is the key direction to establish the synchronization technology system of vegetable water and fertilizer supply and demand for further study on vegetable reduced pressure distillation and leakage control technological system. |
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