Preparation Of Iron Lignosulfonate Fertilizer And Its Effects On Improving Iron Nutrition Of Peanut (Arachis Hypogaea L)

Iron （Fe） is an essential micronutrient element for plant growth. Fe deficiency is a commonnutritional disorder in many crop plants, causing chlorosis, poor yields and reduced nutritional quality.Increasing available Fe levels in major staple food crops is an important strategy to reduce Fe deficiency inpeople. Fe deficient chlorosis can be treated through applying iron fertilizers. Synthetic Fe chelatesapplied in soil or as foliar spray are the most effective solution to control crop Fe deficiency. However,nowadays environmental concerns have enforced the search for new, cheaper, and moreenvironmentally friendly ligands, such as lignosulfonate （LS）. The LS as pulp and paper industrialbyproducts was obtained during the ammonium sulfite pulping process. The optimum syntheticconditions of preparing iron lignosulfonate （LS-Fe） was studied through L₉（3⁴） orthogonal designexperiment （four factors, three levels）. The effects of LS-Fe on plant growth and the re-greening ofFe-deficient peanut （Arachis hypogaea L） crops were assessed with pot experiments and fieldexperiment. The different responses of two peanut cultivars including LH11and YZ9102to Fedeficiency were compared by conducting hydroponics experiments. The influences of LS-Fe addition tonutrient solution or foliar application on the strategies to acquire iron of peanut plants were alsoinvestigated. The main results and conclusions are summarized as followings:（1） The tested LS had the ability of chelating with Fe. Coordination number and stability constantof the LS-Fe complexes were0.62and0.59, respectively, determined by ion-exchange equilibriummethod. The Fe content of LS-Fe product was affected by several factors such as initial pH value in thereaction systems, reaction temperature, Fe rate and reaction time. The factors’ impact sequence was, indecreasing order, pH> temperature> dosage of ferrous ion> reaction time. The Fe concentration andpH value of the LS-Fe, produced under the optimum synthetic conditions, were12.65%and6.98,respectively. Fe was found to be possibly bonded with the carbonyl group（C=O） of LS using Fouriertransform infrared spectroscopy.（2） There was no significant efficacy of application of LS-Fe, FeSO4and EDTA-Fe on shootbiomass and active Fe content in young leaves of peanut plants that had no any Fe deficient chlorosis.However, when the chlorosis symptom was found on young leaves of peanut cultivar YZ9102in thesecond crop time, LS-Fe applied to soil increased the contents of chlorophyll and active Fe in leaves andcould correct the leaf chlorosis. The LS-Fe application had a similar effect in alleviating chlorosis toFeSO4and EDTA-Fe.The results of hydroponics experiment showed that Fe deficient chlorosis could be prevented byLS-Fe addition to nutrient solution or as foliar spay. The chlorophyll content and the active Fe contentof new leaves, and photosynthesis were increased by LS-Fe application. LS-Fe appeared similareffectiveness of controlling Fe chlorosis in peanut plants to FeSO4and EDTA-Fe, and even better thanEDTA-Fe when applied as foliar spay.（3） The appearing time of Fe deficient chlorosis of peanut cultivar YZ9102under no Fe treatment was earlier than that of LH11. The chlorophyll content of new leaves, net photosynthetic rate andchlorophyll fluorescence parameters F_v/F_mwere significantly lower in YZ9102in comparison to LH11when they were subjected to Fe deficiency stress. YZ9102seemed more susceptible to Fe deficiencythan LH11. Without Fe application to peanut plants, pH value in culture medium decreased and Fe³⁺reductase activity of roots increased. Those responses of peanut plants to Fe deficiency were reduced byLS-Fe addition to nutrient solution. When LS-Fe were applied to nutrient solution, the less pH increasein culture medium and the lower Fe³⁺reductase activity were in peanut cultivar LH11compared withYZ9102.In conclusion, lignosulfonate obtained from ammonium sulfite pulping process showed acomplexing capacity with Fe ion and LS-Fe product of optimum efficacy was synthetized successfullythrough this study. Iron nutrition of peanut was improved by LS-Fe applied to soil or foliar sprays.Under Fe deficiency, less pH decrease in culture medium and lower Fe³⁺reductase activity wereobserved in YZ9102in comparison to LH11, which might account for peanut cultivar YZ9102wasmore susceptible to Fe deficiency than LH11. LS-Fe applied to nutrient solution could significantlyalleviate the responses of peanut plants to Fe deficiency.