Regulating Effect Of Potassium Application Stages On Yield And Quality Formation Of Sweet Potato

Regulating effect of potassium application stages on yield and quality formation of sweet potato was studied by using two sweet potato cultivars including Lushu8 which with medium starch and Jishu23 which with high starch in agronomy experimental station of Shandong Agricultural University and Queyu town of Tai'an. The main results were as follows:1 Effects of potassium application stages on yield of sweet potato and its physiological basisPotassium fertilizer application could increase the storage root yield of sweet potato, Jishu23 which with high starch was better sensitive to K than Lushu8. Applying potassium as top cover fertilizer was best favorable to storage root yield growth of Lushu8 and applying potassium as basal dressing was best favorable to storage root yield growth of Jishu23. Meanwhile, increasing production was mainly due to improve fresh weight of single storage root. Applying potassium early (T2, T3, T5) promoted the ratio of big storage root and applying potassium late (T4, T6) promoted the ratio of medium storage root.In this experiment, applying potassium as basal dressing or top cover fertilizer promoted photosynthetic rate, chlorophyll content and LAD at early and middle growth stages of sweet potato and applying potassium as top-growth peak fertilizer increased all the physiological parameters markedly during the late experimental period. Applying potassium early could promote translocation of photosynthate to storeroom to increase storage capacity. Formation and thickening of storage root of Jishu23 was earlier than Lushu8's and net assimilation rate of Jishu23 was higher at early and middle growth stages of sweet potato. The Relationship of Source-sink of Jishu23 was coordinate and it was beneficial to the transportation of photosynthate to storage root. This was the key to high yield of Jishu23. Because the peak of thickening of Jishu23 was earlier, applying potassium as basal dressing was better. Meanwhile, the peak of thickening of Lushu8 was later, so applying potassium as top cover fertilizer promote storage root thickening rate of sweet potato and yield formation.2 Effects of potassium application stages on carbohydrate metabolism of plant, starch accumulation and granule size distribution in storage root2.1 Effects of potassium application stages on carbohydrate metabolism of plant, and starch accumulation in storage rootSoluble sugar content of leaves, petioles and stems decreased after applying potassium. Soluble sugar content of storage root decreased at early and middle growth stages of sweet potato and opposite results were soluble sugar content of storage root increased during the late period. Starch content of leaves, petioles and stems decreased after applying potassium, but the starch content of storage root was increasing throughout the growth period. These results showed that applying potassium increased loading capacity of photosynthate in the source side, unloading capacity of photosynthate in the sink side and increased accumulation rate of starch in the storage root at early and middle growth stages of sweet potato. It increased the storage root yield after applying potassium due to the coordinative relationship between source and sink of synthesis, including the synthesis, transport and transformation of photosynthate. Applying potassium late had short acting time and missed the action time in the first peak period thickening, and also, it is not achieve the best fertilizer.Applying potassium as basal dressing or top cover fertilizer promoted amylase accumulation and all the treatments applying potassium promoted amylopectin accumulation, particular applying potassium later. Applying potassium as basal dressing was beneficial to improving the SS activity at early growth stages of sweet potato and the ADPGPPase activity at early and middle growth stages of sweet potato. Applying potassium as top cover fertilizer promoted SS and ADPGPPase activity of middle growth stages of sweet potato. Applying potassium as top-growth fertilizer increased SS and ADPGPPase activity during the late growth stage of sweet potato. Applying potassium once as basal dressing (T2) and applying potassium as basal dressing and as top cover fertilizer respectively (T5) had high GBSS activities in the whole growth period. Applying potassium once as top cover fertilizer (T3), applying potassium once as as top-growth fertilizer (T4) and applying potassium as basal dressing and as top-growth fertilizer respectively (T6) increased SSS activities. We could conclude that applying potassium late promoted amylopectin accumulation.2.2 The granule size distribution characteristic of starch in storage root of sweet potatoStorage root of sweet potato in harvest time had three-peak structure in the volume and surface area distribution, in which the valley particle diameters were 3.359μm and 7.084μm.A unimodal curve with the granule diameter about 1.204μm at the peak was seen in starch granule number distribution.Potassium application stages had significant effect on the volume distribution of storage root. The results of subdivided ranges of volume distribution showed that a higher volume percentage of diameter <7.084μm granules, was typical of T2 in comparison with other treatments of Lushu8, and opposite results were seen in Jishu23 that the highest volume percentage of diameter <7.084μm granules were T4 and T6. The results also showed that T6 had the highest percentage of diameter 7.084-19.76μm granules in both two cultivars. Meanwhile, T2 had the highest percentage of diameter﹥19.76μm granules in both two cultivars. it is can be concluded that the treatments applying potassium as top-growth peak fertilizer had high highest percentage of small starch granules and medium starch granules and positively the treatments applying potassium as basal dressing had high highest percentage of big starch granules.The analysis of correlation showed that amylase content was very significantly positive correlation with medium diameter and the volume percentage of diameter﹥19.76μm granules. The amylopectin content was significantly positive correlation with the volume percentage of diameter <19.76μm granules and significantly negative correlation with medium diameter and the volume percentage of diameter﹥19.76μm granules. The proportion of amylose and amylopectin was very significantly positive correlation with the volume percentage of diameter <19.76μm granules. This can be suggested that small granules are high in amylopectin contents and big granules are high in amylase contents. 3 Effects of potassium application stages on the absorption and utilization of potassiumApplying potassium reduced potassium efficiency for the production of biomass and storage roots. The treatment applying all the potassium as top cover fertilizer (T3) was the highest potassium efficiency for the production of biomass and storage roots of Lushu8 and applying all potassium as basal dressing was the highest potassium efficiency for the production of biomass and storage roots of Jishu23. Applying potassium as basal dressing and as top cover fertilizer respectively had the highest uptake efficiency of potassium fertilizer of Lushu8 and applying all potassium as basal dressing was the highest uptake efficiency of potassium fertilizer of Jishu23.The agronomic efficiency showed the same law as that of the yield.