Effects of oxalic acid on the nutrient of calcareous cultivated soil and leaf, fruit yield and quality of Rosa roxburghii Tratt.

Abstract:【Objective】Rosa roxburghii Tratt. is a characteristic fruit tree native to southwest China. Its fruit is rich in Vc and other nutrients, and is a high-quality crude material for processing nutritious foods. In recent years, the planting area of R. roxburghii in Guizhou increased to 150 000 hectares, and most of the trees were planted in calcareous yellow soil with high Ca content and soil pH value in Karst areas. Such soil conditions have extremely adverse effects on the growth, yield and quality of R. rox- burghii due to low the availability of soil nutrients as a result of the strong immobilization of soil nutri- ents by massive free CaCO3. It is also difficult to improve soil nutrients by fertilization. Therefore, it is an important problem to be solved urgently in production of R. roxburghii in calcareous yellow soil of Karst areas. The effects of exogenous oxalic acid in improving the nutrient status of calcareous yellow soil and trees of R. roxburghii as well as the yield and quality of fruit were explored in this study in or- der to find a new technical solution for nutrition improvement as well as yield and quality improvement in R. roxburghii in calcareous yellow soil in Karst areas.【Methods】Trees of R. roxburghii Tratt.‘Gui- nong 5’planted in the calcareous yellow soil in Karst area of Southwest Guizhou were taken as materi- als. The experiments were carried out for three consecutive years to study the effects of oxalic acid ap- plication at different applied amounts (0 g, 5 g, 10 g and 15 g per plant) on the nutrient status of calcare-ous yellow soil and the leaf of R. roxburghii, as well as on fruit yield and quality.【Results】The pH val- ue and Ca content could be decreased greatly by the application of oxalic acid. The soil pH decreased from 8.13 to 7.49, 6.93 and 6.54 by applying 5 g, 10 g and 15 g oxalic acid per plant, respectively, while the content of exchangeable Ca decreased from 3 108.25 mg·kg-1 to 2410.76 mg·kg-1, 1 906.39 mg·kg-1, and 1 353.88 mg · kg- 1, respectively. Compared with the control, the activities of urease, nitrate reduc- tase, alkaline phosphatase, Fe3+ reductase and protease in the soil were significantly higher; the contents of available nutrient elements except for exchangeable Ca were also increased; the number of bacteria, fungi, actinomycetes, azotobacters, inorganic phosphorus bacteria, organic phosphorus bacteria and po- tassium bacteria increased as well. In the three treatments, application of 10 g oxalic acid per plant had the highest contents of available N, P, K, Fe and B in the soil, highest activities of urease, nitrate reduc- tase, alkaline phosphatase and Fe3+ reductase, and maximum numbers of functional bacteria. With high- er oxalic acid applied, the contents of exchangeable Mg and available Mn, Cu and Zn in the soil in- creased. The contents of N, P, K, Mg, Fe, Mn, Cu, Zn and B in the leaves of R. roxburghii treated by ox- alic acid were significantly higher than those in the control, and the treatment of 10 g oxalic acid per plant had the highest contents of N, P, K, Fe, Zn and B in the leaves. With the increase in application amount, Ca content in the leaves decreased significantly but Cu content increased dramatically. Fruit set, single fruit weight, fruit yield per plant and contents of soluble solids, total soluble sugars, total ac- ids and Vc in the fruit were also increased by applying oxalic acid. The highest yield and best quality were obtained by the treatment of 10 g oxalic acid per plant.【Conclusion】The application of oxalic ac- id could significantly improve the contents of available nutrients in the yellow calcareous soil in Karst areas, and improve the microbial population structure in the soil, increase the activities of nutrient en- zymes in the soil, and increase leaf nutrient and fruit yield and quality. In the experiment, applying 10 g oxalic acid per plant proved to be the most effective in increasing the fruit yield and quality of R. rox- burghii grown in the calcareous soil.