Effects of different potassium nutrition on growth and rootmorphological traits of watermelon seedling

The study was carried out by a pot experiment supplied with five K levels 0 (K0), 60 kg·hm^?2 (K1), 240 kg·hm^?2(K2), 500 kg·hm^?2(K3), 700 kg·hm^?2(K4) to probe into effects of different application of potassium fertilizer on watermelon seedling growth and root morphology traits. Results indicated that under 240 kg·hm^?2 potassium application, stem fresh weight, leaf fresh weight, stem dry weight, leaf dry weight, leaf area, stem diameter, plant height, total root length, specific root length, surface area, root volume, root tips and root average diameter were 46.05%, 31.31%, 57.56%, 29.87%, 2.92%, 12.71%, 37.18%, 67.23%, 64.00%, 64.03%, 58.88%, 154.11% and 6.25% higher than those under no potassium application. Under 700 kg·hm^?2 potassium application, stem fresh weight, leaf fresh weight, stem dry weight, leaf dry weight, leaf area, stem diameter and plant height were 40.24%, 25.31%, 36.90%, 23.08%, 31.09%, 9.81% and 41.44% lower than those under 240 kg·hm^?2 potassium application. The effect of 700 kg·hm^?2 potassium application on root morphological traits were not obvious. Additionally, the root length in root diameter ≤ 1.0 mm was above 90%, the root tips in root diameter range ≤ 0.5 mm was above 98%, specific root length, surface area and root volume in root diameter ≤ 2.0 mm was above 50% of total amount, respectively. Root length, specific root length, surface area and root volume of root diameter ≤ 2.0 mm, 2.5 mm < diameter ≤ 3.0 mm, 3.5 mm < diameter ≤ 4.0 mm were significant affected by K level. Morphological traits were determined by specific root length, surface area, root volume and tips in root diameter ≤ 2.0 mm. Because of relatively stronger absorption and the largest proportion of fine roots, the impact of potassium deficit on potassium nutrition of watermelon seedling was more serious than that on roots growth. Appropriate potassium concentration was beneficial to the growth of watermelon seedlings, it could improve the quality of seedlings growth, root growth and development. No potassium application and high potassium restrained the growth of seedlings, but the inhibition of high potassium on the root growth was not obvious. Under this experimental condition, the 240 kg·hm^?2 potassium application treatment was the best.