Potassium Absorption Character Of Watermelon And Substitution Effect Of Potash Fertilizer By Straw

With the increasing of crop yield and multi-cropping index, the potash demand is rising. Potassium resource is shortage in China. It is necessary to exploit potassium resource and study reasonable application method of potash for relieving potash stress. Watermelon is one of the main economic crops in Jiangsu province. Watermelon has short growth period and is sensitive to potassium application. Experiments were carried out to investigate the rule of potassium absorption by watermelon, the effect of foliar potassium nutrient and the effect of substitution of potash by straw on the yield and quanlity of watermelon. The results are as follows:1. The quantity and rate of potassium absorption of watermelon is different in each stage. Watermelon is sensitive to potassium at the former stage. Compared with other treatments, the potassium content in root, stem and leaf of watermelon were highest when 45-90 kg ha-1 of K2O was applicated as basal fertilizer. Watermelon has less need of potash at the early stage of the growth period, only can meet the needs of growth period at the early stage. But in the last stage of the growth period of watermelon, especially in the fruit expanding process, the rate of potassium absorption increases doubly, the potassium absorption rates on the last two periods of watermelon seedling is in the percent of 67.9 and 14.5.180.0 kg ha-1 K2O application at fruiting stage is suitable to adapt for the potassium requirement. Compared with other treatments, the dry matter of watermelon is the highest at 300.0 kg ha-1 of K2O application, as well as the potassium absorption and soluble sugar content. Soluble sugar content and acid content of watermelon pulp is rising before the decline with the potassium application increased. The content of soluble sugar and the acid content were lower at 450 and 600 kg ha-1 potash application than that at 300.0 kg ha-1 treatment.2. Nitrogen nutrient of watermelon was influenced by potash application. At creep stage, nitrogen absorption was suppressed by high potash supply. At fruiting stage, the highest nitrogen was absorbed at 300 kg ha-1 of K2O application. The results suggested that watermelon has less need of nitrogen at early stage of the growth period, and nitrogen absorption would be depressed in the number of higher concentration of K2O. Expanding period is the vigorous growth period, and until mature period, the effect of management of K300 is the most significant in increasing production.3. Potassium nutrient of watermelon could be supplied by straw. Partial replacement of potash fertilizer by straw effected the potassium content of root in early period, especially on the stems and leaves in later period. The potassium absorption would be increased by straw replacing. The effect on watermelon yield increased obviously, with the yield of T2 and T4 treatment take the second place. In the reason of effective microorganisms, the straw decomposition is promoted obviously, so the amount of potassium content of T3 treatment is more over than the potassium absorption limit, and the treatment of T2 would be the optimum treatment. Soluble sugar content decreases at first, and then rises. The effects of straw substituting for potash fertilizer to soluble sugar content of watermelon are not obvious, so as to the acid content.4. Potassium nutrient by foliar application can improve the yield of watermelon under the condition of suitable quantity of potassium. But the production would be increased above the number of 300.0 kg ha-1 of K2O. In the number of 300.0 kg ha-1 of K2O, the soluble sugar content is the highest, so as the acid content, and the content of soluble sugar and the acid content begin to decline when the application of K2O is above 300.0 kg ha-1.