Physiology Basis Of Quality Improvement By Applying Humic Acid And Potassium Fertilizer To Edible Sweetpotato

In order to find out the physiology basis of quality improvement of edible sweetpotato caused by humic acid and potassium fertilizer, an experiment was carried out in agronomy experimental station of Shandong Agricultural University with Beijing 553 and Jishu 22. The main results were as follows:1 Effect of humic acid (HA) on yield and nutrient quality of storage root1.1 Effect on yield of storage rootFor Beijing 553 yield in treatments with HA application were increased, thereinto yield effects of treatment HA17 reached the significant level. For Jishu 22 yield in treatments with HA application were increased without significant difference. The yield of different varieties were increased by HA application in different ways. Yield of Beijng 553 was increased by means of increasing fresh weight per lump. In other words HA could facilitate the change from mid-tuber and small-tuber to big-tuber. The reason of increasing yield for Jishu 22 was to increase storage roots lumps per plant. That was caused mainly by increasing the amount ratio of big-tuber.1.2 Effect on nutritional quality of storage rootAmylose content was reduced significantly and amylopectin content was reduced lightly after HA application which resulted in lower starch content of storage root. The reduction of rate of amylopectin to amylose content was caused by HA application which was benefit to taste of storage root. Treatment with HA application got higher soluble sugar content of storage root than that of storage root in the control, in addition the amplification of soluble sugar content was bigger than the decline rate of starch content. These declared that one of the reasons for increase of soluble sugar was to improve conversion from starch to soluble sugar.After the application of humic acid sucrose phosphate synthase activity was significantly increased in functional leaves, sucrose content in functional leaves were also significantly increased, the sucrose content of vine was decreased or similar, in addition insoluble acid invertase and alkaline invertase activity in storage root were increased significantly, all of these showed that application of humic acid could increase the supply of photosynthetic products, keep clear of photosynthate transport corridors and improve the offloading capabilities of storage root to ensure the supply of sucrose. The activity of sucrose synthase was decreased which gave rise to the diminution of starch synthesis and the increase of sucrose accumulation by use of HA; amylase activity was increased also by use of HA which brought less starch content and higher glucose content compared with the control; treatment with HA also got higher fructosan content by means of increasing SST activity than that of the control. HA increased the accumulation of fructose and glucose by means of increasing soluble acid invertase activity as well. To sum up, humic acid could increase the soluble sugar content in storage root by three ways: first, to enhance the supply of soluble sugar to storage root; second, to inhibite the conversion from soluble sugar to starch of storage root; last, to promote the conversion from starch to soluble sugar in storage root.The result got by determining the content of vitamin C during the key stages of growth showed that the main periods of accumulation of vitamin C in storage root were middle-late stage of growth for Beijing 553, while that for Jishu 22 were intermediate and final growth phases. Vitamin C content was significantly increased by use of HA.The result got by determining the content of nitrate during the key stages of growth showed that the main periods of accumulation of nitrate in storage root were middle-late stage of growth for Jishu 22, meanwhile treatments with HA got lower nitrate content than that of the control. The result got from Beijing 553 showed the amino acid content in storage root was increased during the key stages of growth, that meant HA could improve quality of storage root by the way of improving the changes from nitrate to ammoniacal nitrogen.2 Effect of K on yield and nutrient quality of storage root2.1 Effect of K on yield of storage rootAdding potassium fertilizer might significantly increase yield of storage root, but the reasons for yield increase were different among varieties. Both cutting storage roots lumps per plant and fresh weight per lump were increased by potassium application in Beijing 553. The main reason was potassium application could increase amount ratio and mass ratio of big-tuber. Yield of Jishu 22 was increased after using potassium by means of increasing storage roots lumps per plant.2.2 Effect on nutritional quality of storage rootPotassium could improve soluble sugar content of storage root markedly, starch content in storage root was increased as well. The increase of soluble sugar was caused by increase of all components of soluble sugar, while the increase of starch was caused by increase of amylase content mainly.The physiological causes of increasing soluble sugar content by use of potassium were similar to humic acid: potassium could enhance the supply of photosynthetic products, and keep clear of photosynthate transport corridors, meanwhile improve the offloading capabilities of storage root to ensure the supply of sucrose; in addition potassium could improve the content of fructose and glucose by means of increasing the activity of soluble acid invertase as well; besides fructan content was increased by increasing SST activity after potassium application. The effect of potassium on the activity of SS was different from HA. Potassium could improve the synthesis of starch, while content of starch in storage root was increased lighly caused by increase of amylase activity with potassium application mainly which resulted in lower starch content and higher soluble sugar content.The quality of storage root was improved by use of potassium via increasing content of Vitamin C and decreasing content of nitrate.