| As the Chinese nation’s traditional treasures, the planting technology of intercropping made tremendous contributions to solve the problem of feeding the world population. The relay strip intercropping of maize and soybean has been practiced traditionally in a large scale in south of China, and the planting area is rising continuously. It has been listed as main agricultural technology of Ministry of P. R. China since2008, as it is worth to be enhanced and further applied in sourthern China. However, there exsited a symbiotic period in this system, the earlier-planted and taller maize form relatively higher canopy structures than soybean and the roots of maize grow to a greater depth than those of soybean, thus the lower soybean seedling grows in the condition of shading by taller maize, the maize intercepts more sunlight than soybean. So, the soybean yield and quality are suppressed, mainly due to soybean suffered adverse competition in environment resources such as water, nutrients and radiation from maize, which leads to thinner stem, elongated plant and weaker lodging resistance, easier to lodging. In this study, the trials of pot and field were carried out from2008to2010to investigate the effect and mechanism of potassium on lodging-resistance and yield improvement of relay strip intercropped soybean. The main purpose was to open out essential of lodging of relay strip intercropping soybean, the principle of lodging-resistance and yield improvement of potassium, and which can be applied in optimizing the system of cultivation technology of relay strip intercropping soybean, providing the theory basis for reasonable fertilization application. The main results showed as follows:1. Applying the technology of pot trial simulated the field trial, the root growth and their relationship with lodging of sole and relay intercropping soybean under different potassium levels were studied. The results indicated that potassium application increased the number of first lateral roots, total length of lateral root, root day matter weight and root/shoot ratio of soybean, but the differences were not significant in main root length and root volume. The study of physiological characteristic in root suggested that the bleeding sap, bleeding sap-top ratio and root vigor increased first and then decreased with the increment of potassium application in sole and relay strip intercropping systems. The treatment in middle potassium level was the highest, which were1.84g-plan-1,0.35and38.58μTPF·g-1FW·h-1, respectively. The bleeding sap and bleeding sap-top ratio of relay strip intercropping soybean were3.95and4.90times higher significantly than monocropping soybean, but it was opposite in the root vigor. According to the correlation analysis, the resulted revealed that lodging rate of soybean was negatively correlated with root volume, the number of first lateral root, total length of lateral root, root dry matter weight and root/shoot ratio. The soybean with bigger root volume, more number of first lateral roots, and higher root/shoot ratio, and then it was not easy to lodging. Appropriate potassium application improved the root growth of soybean, increased the stationary ability of plants, and reduced the actual lodging rate. 2. The pot and field trials were carried out to investigate the relationships between stem trait and lodging resistance of sole and relay strip intercropping soybean under different potassium levels. The results showed that appropriate potassium application could increase the basal stem diameter, plant erection degree, mechanical strength, lodging resistance index and dry weight of basal internode, but reduce the plant height, basal internode length, height of central of gravity and lodging rate. The stem lodging resistance index was positively correlated with basal internode diameter and mechanical strength, but negatively correlated with plant height, height of central of gravity, basal internode length and lodging rate. The lodging rate was positively correlated with plant height, height of central of gravity and basal internode length, but negatively correlated with basal internode diameter of stem, mechanical strength, and lodging resistance index, the similar relationship was expressed in pot and field trials. The proper potassium application could improve the lodging resistance index of stem in relay strip intercropping soybean, reduce the actual lodging rate.3. According to the morphology anatomy and microcosmic observation, the main effect of potassium on basal internode structure of soybean stem was increasing the thickness of xylem and ratio of xylem in stem cross-section, reducing the number of vascular bundle, but increasing the single area of vascular bundle. The irregular changes occurred in thickness of phloem and phloem fiber when increased the potassium application amounts. Potassium could increase the pith area and thickness of cortex, reduce the ratio of pith in stem cross-section, but the change in thikcness of cuticula was not significant. Under the sole and relay strip intercropping systems, the thickness of cortex, area of vascular bundle, thickness of xylem and phloem, area of xylem and phloem in stem cross-section, cambium thickness, area of pith and ratio of pith in stem cross-section in relay strip intercropping soybean were significant lower than that of monocropping soybean, but the differences in thickness of cuticula and number of vascular bundle were not significant. The difference of basal stem diameter in different treatments was responsible for the difference in thickness of xylem and size of vascular bundle.4. Potassium application increased significantly the soluble carbohydrate content, K content, C/N ratio, phenylalanine ammonia lyase (PAL) and cinnamyl alcohol dehydrogenase (CAD) activity, which increased first and then decreased with the increasing of potassium application amount, but the nitrogen content in different treatments were not significant. Applied potassium significant improved the content of lignin and cellulose, which were5.3%～11.2%and8.7%～19.9%higher than treatment without fertilizer respectively. In monocropping and relay strip intercropping systems, the soluble carbohydrate content of stem and K content in monocropping soybean were higher than relay strip intercropping soybean. The lignin and cellulose content, PAL and CAD activity of monocropping were also higher than relay strip intercropping soybean at seedling stage, but the differences were not significant at full-bloom stage, the nitrogen content and C/N ratio were also not remarkable. The lignin content of stem was positively correlated with PAL and CAD, the higher activity of PAL and CAD, and the more lignin content. Potassium application improved the content of IAA, CTK and ABA, CTK/ABA ratio in soybean leaves at seedling and full-bloom stage, reduced the GA3content and GA3/CTK and IAA/CTK ratio at seedling stage, enhanced the horizontal growth of stem. The GA3 content of leave at full-bloom stage increased first and then decreased with the increment of potassium application, and the IAA/CTK and GA3/CTK ratio increased with the increasing of potassium applied, which resulted in stronger vertical growth of stem.5. Applied the potassium increased the chlorophyll content and SPAD value of leaves at earlier growth stage of soybean, which increased first and then decreased with the increasing of potassium application amount, it was more obvious in relay strip intercropping system. The net photosynthetic rate (Pn) and stomatal conductance (Gs) of monocroppping soybean were33.9%and17.7%higher than that of relay strip intercropping soybean respectively, but the intercellular CO2concentration (Ci) showed the opposite trend. Proper potassium application increased the Pn and Gs of monocropping and relay strip intercropping soybean, reduced the Ci of leave. The soybean shading by maize in relay strip intercropping system showed higher initial fluorescent (Fo) and actual photosynthetic ability than monocropping soybean, but the maximal photochemical efficiency of PS Ⅱ in the dark (Fv/Fm) and nonphochemical fluorescence quenching (NPQ) were opposite. The difference of photochemical efficiency of PS Ⅱ in the light (Fv’/Fm’) and NPQ between monocropping and relay strip intercropping system were significant, excepted the Fv/Fm. Potassium applied increased the minimal fluorescence (Fo) and Fv’/Fm’ of soybean leaves, reduced the Fv/Fm, photosynthetic active fluorescence quenching (qP) and NPQ, but the difference in these treatments were not significant.6. The dry matter accumulation of relay strip intercropping soybean followed a S curves, could be described by Logistic regression equations (y=k/(1+ae-bx))(R2＞>0.99**). Proper potassium applied improved the dry matter accumulation of relay strip intercropping soybean. With the increasing of potassium applied amount, the dry matter accumulation and maximum growth rate increased, the time of maximum growth rate and dry matter accumulation rate began to rapid increase were advanced. Increased the amount of potassium could adjust the dry matter output, and increase the contribution ratio from vegetative organ to pod. The amount of dry matter accumulation, output and contribution ratio increased remarkable with the increment of potassium application amount.7. Potassium application significant increased the yield and pod number per plant in soybean, but there was no effect on seed number per pod, and the100-seed weight showed different trends in field and pot trials respectively. In the monocropping and relay stip intercropping systems, the yield, pod number per plant, seed number per pod and100-seed weight of monocropping soybean were significantly higher than that of relay strip intercropping soybean shading by maize. Adopting the different potassium applied ways suggested that the treatment of potassium was applied before planting and at seedling and initial flower stage with the ratio of1:1:1were the highest among the test treatments, being2001.27kg·hm-2, but the seed number per pod and100-seed weight were not significant. In the field trial, the potassium applied significantly increased the protein content of relay strip intercropping soybean, reduced the crude fat content. In the pot trial, the protein content of different treatments was not significant difference. The potassium applied ways indicated that the treatment of potassium was applied before planting and at seedling stage with the ratio of1:1was beneficial for the increasing of protein content, but which had no effect on the crude fat content.8. In the relay strip intercropping system of maize and soybean, applying potassium could improve the morphology of root and stem, shape good plant type, increase the lodging resistance, reduce the lodging rate, and then improve the yield and quality of soybean. |
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