الفهرس 
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Abstract
The objective of this work is to study the chemical characteristics of humic substances (HA&FA) isolated from different sources and study the effect of the extracted fulvic acids on the growth and chemical composition of spinach plant grown on a sandy soil.Three sources were collected from clay soil, compost and clover straw.The humic substances (Humic & Fulvic acids ) were extracted from different sourc using 0.1N KOH solution, and purified according to the method of Sanchez- Monedero et al. (2002). The obtained results can be summarized as follows:-Humic and fulvic acids characteristics:The analysis of carbon and nitrogen of the studied humic acids and Fulvic acids proved that these elements affected slightly by the source of humic substances. Humic and fulvic acid extracted from soil is more mature than compost and clover straw.Total acidity, COOH groups and phenolic OH groups content were differed with the sources of humic and fulvic acids. The fulvic acids content of total acidity, COOH groups and total- OH groups are higher than the humic acids.The IR spectra of the studied humic and fulvic acid showed that there are a big similarity among the different sources. IR spectra indicated that humic and fulvic acids had aromatic rings besides aliphatic compounds and include COOH, COO-,OH, C=O and C-O groups in their structures.Pot experiment A pot experiment was conducted in the farm of the Faculty of Agriculture, Mansoura University in the winter season of 2017 aiming to evaluate the effect of fulvic acid extracts on the chemical composition and yield of spinach plant (Spinacia oleracea) grown on a sandy soil. Spinach (Spinacia oleracea) was cultivated in March 19,2017 in closed plastic pots. Each pot was filled with 10 Kg soil and 10 seeds were sown in each pot. Sandy soil was taken from Kalabsho Farm Fac. of Agric., Mansoura Univ., Dakahlia Government. The soil was rinsed with tap water three times before using as growth medium.The experiment was carried out in a completely randomized design with 6 replicates. The experiment included 4 treatments as follows:Without fulvic acid application. Application of fulvic acid extracted from soil at a rate of 10 L fed-1.Application of fulvic acid extracted from compost at a rate of 10 L fed-1 Application of fulvic acid extracted from clover straw at a rate of 10 L fed-1.Irrigation was applied to reach the field capacity and the assumed field capacity was readjusted every 5-7 days. Mineral fertilizers were applied at rates of 100 Kg fed-1 Ammonium nitrate, 150 Kg fed-1 super phosphate and 50 Kg fed-1 potassium sulphate after 15 days from planting.The obtained results would be summarized as follows:The results of the present study showed that the effects of different sources of fulvic acid on fresh and dry weights, N%, P%, K% and Fe ppm were significant. The results indicated that the highest values of fresh and dry weight of shoot and roots at fulvic acid that extracted from soil treatment. Also, the nutrient uptake (N, P, K, Fe) of spinach was significantly increased by adding fulvic acid that extracted from soil.Regarding the effect of fulvic acid under study it can be observed that fulvic acid extracted from soil was superior for increasing the available content of soil from N, P, K and Fe mg kg-1, while the lowest level was recorded for the control treatment. Also, the content of organic matter was significally increased by adding fulvic acid that extracted from soil, while the lowest level was recorded for the control treatment.Conclusions According to the obtained results of studying chemical analysis and infrared Spectrophotometry it can be concluded that the humic acid and fulvic acid which extracted from soil are more humified than the other humic acids. Based on the obtained results of this study it can be concluded that the addition of fulvic acid that extracted from soil significantly increased the plant growth and mineral contents of spinach plant, as well as increasing the mineral contents of soil and organic matter.