| The obstruction factor of affecting the growth of citrus was confirmed by the investigation on nutrients contained in Yichang Citrus Reticulata. Also, soil acidification and general lack of microelement were discussed. By acidic soil remediation under different dosages of lime in fields in two consecutive years, microelement fertilizer correction of two points in three consecutive years. And through pot experiment, the comparative study was conducted on remediation effect of different dosages of lime and biochar on acidic yellow brown soil in two consecutive years. Additionally, the remediation effect of biochar of different materials was observed on acidic yellow brown soil. The main results were as follows:1. The investigation on nutrients of Citrus Reticulata in producing area of Yichang City was found that:soil acidification of large area significantly existed in the producing area of Citrus Reticulata in Yichang City, especially in Yidu City, Zhijiang City, Banyue Town and Wangdain Town in Dangyang, Yaque ling Town and Longquan Town in Yiling District, among which lime should be reasonably used to improve soil acidification. Meanwhile, N and K deficiency were observed in the producing area of Citrus Reticulata in Yichang City. So N and K fertilizer should be attached importance to and P fertilizer be controlled. Microelement deficiency of B and Zn was observed. So in Longquan Town and Xiaoxi ta Town in Yiling District, organic fertilizer should be increasing applied due to low levels of organic matter. Also, Mg fertilizer should be added appropriately in Yidu City and Longquan Town and XiaoxitaTown in Yiling District. The correlation analysis on fruit quality and Leaf nutrient showed significant correlation between fruit total soluble solids (TSS) and leaf nutrient. The fruit titratable acid (TA) showed a highly significant negative correlation with P, Ca in leaves, a highly significant positive correlation with K, Mg and Cu in leaves and a positive correlation with Fe and Mn in leaves. And TSS:TA was observed to have a highly significant positive correlation with P, Ca in leaves, a highly significant negative correlation with K, Mg in leaves and a significant negative correlation with Fe, Mn, Cu and Zn in leaves. Additionally, the fruit Vc content showed a significant negative correlation with P, Ca and B in leaves and a significant positive correlation with K and Cu in leaves.2. The effects of application of B, Zn or their combination on the soil B and Zn contents, leaf and fruit B and Zn contents, and citrus fruit yield and quality. In the acid yellow brown soil, the soil application of borax was a rapid and effective measure to cure citrus B deficiency, application of borax could improve soil and leaf B contents in this first year, but increased citurs yield significantly in the third year. Although soil application of zinc sulfate could improve the soil available Zn contents, it is need at least three years of continuous application to cure citrus tissue Zn deficiency and improve fruit quality. B and Zn affected fruit yield and quality in different ways. The yield increased after the application of B was due to the augmentation of the fruit number, while fruit quality was improved by Zn. the co-application of B and Zn could both improve the fruit yield and quality. Therefore, in the acid yellow brown soil with low B and Zn availability, soil application of40g zinc sulfate and20g borax per tree could effectively increase cure Zn and B deficiency using the method of root-irrigation, and increase yields and quality in Satsuma mandarin with a continuous application over at least three years.3. The effects of varying applications of Fe-EDDHA, Zn and Mn combinations on the soil Fe, Mn and Zn contents, leaf and fruit Fe, Mn and Zn contents, and citrus fruit yield and quality. Soil available Fe and Zn concentrations were raised significantly through the application of Fe-EDDHA and Zn, whereas the soil available Mn concentration was not increased through the application of Mn. In the second year, Fe-EDDHA alone or co-application of Mn and Zn raised the leaf active Fe content significantly without influencing the leaf and fruit Fe concentrations. The Zn concentrations in leaf and fruit decreased when Fe-EDDHA was applied exclusively, but increased when Fe+Zn and Fe+Zn+Mn were applied in the third year. There was no significant difference in leaf and fruit Mn concentrations among all treatments. All of the treatment increased the fruit number, particularly Fe+Zn. Although Fe-EDDHA alone did not influence fruit total soluble solid (TSS), it did sharply decrease fruit titratable acid (TA) and increase TSS:TA. Fruit TSS, TA and Vc content were raised significantly through the application of Fe+Zn and Fe+Zn+Mn. In conclusion, the application of Fe-EDDHA alone could induce zinc deficiency, and Fe and Zn play different roles that affect fruit yield in calcareous soil. The citrus fruit number was mainly affected by Fe while the mean fruit weight was improved by Zn. Moreover, Zn was a more important factor than Fe in improving the citrus fruit quality. Therefore, soil application of60g Fe-EDDHA and20g zinc sulfate per tree could effectively increase cure Fe and Zn deficiency and increase both yield and quality in Satsuma mandarin in calcareous soil.4. The effects of different application rate of lime were studied on soil acidity of acidic soil in citrus orchard, nutrient availability, nutrient uptake of trees and yield and quality of fruit. The dynamic changes of different mineral nutrients and accumulative laws varied with each other in satsuma mandarin leaves. As a whole, N, P, K, Ca, Mg and Mn in mature leaves appeared from low to high, however, Fe showed from high to low. According to the newborn early-spring leaves, P, N, Mg and Cu started to accumulate before fruit expansion period, Mn started to accumulate before colour-changed period, Ca and Fe showed stably continuous accumulation in the whole growth period, however, K and Zn mainly accumulated in young fruit period, and gradually decreased with the increasing growth accumulation of fruit. In addition, lime treatment of medium and high amount could effectively neutralize the topsoil acidity and improve the effectiveness of P, Ca and Mg in soil and absorption of K and Mg in trees, while reducing the effectiveness of N, Fe, Mn, Cu and Zn in soil and the absorption of Mn in trees. Meanwhile, the fruit titratable acid (TA) could be increased by liming, and the TSS/TA be increased. Threefore, acidity of citrus fruit could be caused by soil acidification, and with liming, fruit quality may be affected by absorption promotion of P and Ca and inhibition of Mn. So, for acidification of citrus orchard with yellow brown soil, the application rate of2kg/strain was recommended in fields using the method of surface broadcasting.5. The effects of different dosages of lime and biochar were observed on soil acidity, microbiologic properties, nutrient availability, nutrient uptake of satsuma mandarin trees and fruit quality. Lime and biochar could effectively increase the soil PH and neutralize soil acidification. However, remediation effect of lime would decrease with the extension of time, but biochar showed more lasting effect. With the application rate of lime and biochar increasing, microbial biomass tended to first rise and then drop, along with the increase in soil respiration. Compared with low and medium amount of lime and biochar treatment, the high amount treatment significantly increased microbial activity, although lowering the microbial biomass. The improvement of biochar on absorption of soil and tree nutrients was superior to that of lime due to its abundant mineral nutrients. Additionally, soil acidity could be neutralized by biochar, and as a fertilizer source, it could improve soil fertility and increase the absorption of nutrients in plants. Furthermore, the content of titratable acid (TA) in satsuma mandarin fruit could be decreased with the application of lime or biochar, and TSS.TA could be increased with the medium amount of lime, along with medium or high amount of biochartreatment. In addition, the application of lime and biochar could reduce the acidity and increase TSS:TA due to the probable absorption promotion of P in trees and absorption reduction of Fe, Mn and Cu. Biochar had the better promotion effect on fruit quality than lime, particularly BC-2. For the lime, L-2(2.4g/kg) had the best effect on fruit quality promotion, L-2could decrease the TA by16.2%, and increase the TSS/TA by21.8%. For the lime, BC-2(2%) had the best effect on fruit quality promotion, BC-2could decrease the TA by25.0%, and increase the TSS/TA by31.7%.6. The effects of biochar derived from three feedstocks on the acidity, chemical and microbial properties of the acidic soil, nutrients absorption and growth of trifoliate orange seedlings (Poncirus trifoliata L.) were studied. All of the three biochars derived from three feedstocks could neutralize soil acidity and increase soil pH. However, only peanut hull biochar significantly increased plant growth and the biomass of trifoliate orange seedlings. Soil microbial biomass C and basal respiration were increased by peanut hull and rice straw biochar, particularly peanut hull biochar. The effect of three biochars on soil enzyme activity is various, but the GMea of the assayed enzyme activities increased47.2%,36.9%and25.8%by peanut hull, rice and rape straw biochar, respectively. Biochars decreased soil available N, Fe, Mn, Cu and Zn contents, But it markedly increased the the Fe, Mn, Cu, Zn allocation proportion in the tissue of aboveground of trifoliate orange seedlings, particularly rape straw biochar. rice straw and rape straw biochars which had more abundant mineral nutrient contents, as the fertilizer source had better enhancement effect for the soil and plant mineral nutrient contents compare to the peanut hull biochar, while peanut hull biochar resulted in higher plant nutrients accumulation due to the improvement of biomass of trifoliate orange seedlings. although the three biochars effectively neutralized soil acidity, peanut hull biochar had the greater positive effect on trifoliate orange seedlings growth, and secondarily rice straw biochar. The positive effects were not related to soil and plant nutrients, but to the soil microbial biomass and enzyme activity. |
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