Effect of Humic Acid and Foliar Application of Different Potassium Sources on Yield, Quality and Water Use Efficiency of Sweet Potato Grown under Drip Irrigation in Sandy Soil

Ahmed E. Abd- All, Ashraf E. El-Namas and Essam M. EL-Naggar

field experiments were conducted at El-Bostan area at Aly Mubark experimental farm south Tahrir region, El Behira Governorate (300 54 N, 290 52 E, and 25 m above sea level), during 2012/2013 and 2013/2014 to study the effect of humic application with/without foliar application of different potassium source (potassium nitrate, potassium silicates, potassium humate, potassium sulphate) on sweet potato yield and quality characteristics under drip irrigation system. The results indicated that humic acid applications significantly increased the total tuber yield and all measured growth parameters of sweet potato. The relative increases of total tuber yield, marketable tuber yield, average tuber weight, tuber dry weight, foliage dry weight and leaf area were 6.64, 5.24, 7.47, 19.07, 4.35 and 7.92 %, respectively. Humic acid applications significantly increased total nitrogen, potassium and phosphorous content of sweet potato tubers. Also, foliar application of different potassium sources significantly increased total tuber yield of sweet potato and the most of quality characteristics. Potassium nitrate (KN) and potassium silicates treatments have the highest ability to increase the yield and other growth parameter than other potassium sources (potassium humate and potassium sulphate) under sandy soil condition. Interaction effects between humic acid and foliar application of different potassium sources indicated that there was a significant effect between soil application (fertigation) of humic acid and the foliar application of different potassium sources except for tuber potassium and phosphorus content and also, for available nitrogen, potassium and phosphorous in soil at harvest stage. Calculated water use efficiency (WUE) for total tuber yield increased with increasing rates of soil application of humic acid for the two growing season (2012/2013-2013/2014). Relative increases in WUE for total tuber yield were 4.46 and 11.65 % for HA2 and HA4, respectively as a mean value of the tow growing seasons. Also, WUE for marketable yield were more affected by soil application of humic acid compared to WUE for total yield, where the relative increases were 6.07 and 14.51 % for HA2 and HA4, respectively as a mean value of the tow growing seasons. Potassium silicate have the highest WUE for  total tuber root yield values 3.76 ton/m3 followed by potassium nitrate 3.61 ton/m3 while potassium sulphate have the lowest WUE for total tuber root yield  3.20 ton/m3 as a mean values of the two growing season. It can be concluded that  humic acid at rate of 4 kg/feddan with potassium silicate as a foliar application was good practice to increase sweet potato production under sandy soil condition.

Keywords: humic acid, foliar application, yield, water use efficiency, sweet potato, drip irrigation, sandy soil.