Yield response of cassava Huay Bong 80 variety grown in an Oxyaquic Paleustult to cassava starch waste and nitrogen fertilizer

A field experiment was carried out in Na Yia district, Ubon Ratchathani province, Thailand during the 2015–2016 cropping season to investigate the response of cassava to cassava starch waste (CSW) and nitrogen (N). Split plots in a randomized completed block design with four replications were established in an Oxyaquic Paleustult soil type. The main plot consisted of five rates of CSW (0 t/ha, 6.25 t/ha, 12.5 t/ha, 25 t/ha or 50 t/ha). Six rates of N (0 kg/ha, 25 kg/ha, 50 kg/ha, 75 kg/ha, 100 kg/ha or 125 kg/ha) were applied to subplots. The addition of CSW at rates of 12.5 t/ha, 25 t/ha or 50 t/ha produced significantly higher fresh tuber and starch yields and starch content. The CSW applied at the rate of 50 t/ha produced the significantly highest aboveground biomass, but with the lowest harvest index. Applying 75 kg/ha or 100 kg/ha of N produced significantly higher fresh tuber and starch yields. The respective highest fresh tuber and starch yields were obtained from the combination of 75 kg/ha of N and 12.5 t/ha of CSW as soil amendment. The concentrations of P, Ca, Mg, S and Zn in tubers significantly increased with increments of CSW. Furthermore, the CSW also significantly enhanced the nutrients stored in the topsoil after growing cassava for one crop.