Cassava nutritive characteristics of NPK and effect of fertilizer application

Cassava (Manihot esculenta Grantz), a perennial shrub belonging to the family of Euphorbiaceae, is grown in Guangdong and Guangxi Provinces of China. Cassava root develops into tubers that form an important source of dietary and industrial carbohydrates. Cassava is the most competitive biofuel crop in terms of clean energy (ethanol and hydrogen) production because of its high starch content and high level of production. Cassava yield is significant related with nutrient content of the plant. To analyze the effects of N, P₂O₅ and K₂O contents at different growth stages seedling stage (SS), tuber root formative stage (TRF), early tuberous root growth stage (TRG), rapid root bulking stage (TRB) and maturity stage MS) of different cassava varieties, a field trial with five fertilization treatments NP, NK, PK, NPK (in these treatments, the application rates of N, P, and K were 360 kg(N)·hm^-2, 144 kg(P₂O₅)·hm^-2, 360 kg(K₂O)·hm^-2), and CK (no fertilizer application) and two varieties (newly developed ('SC5') and conventional ('SC205') was carried out. Results showed that cassava root yield had significant positive correlation (P < 0.01) with N content at TRF, TRG and TRB stages, and with K₂O content at SS, TRG and TRB stages. Starch content of cassava root had significant positive correlation (P < 0.01) with N content at TRF stage. It had significant negative correlation (P < 0.01) with P₂O₅ content at SS and MS stages, and with K₂O content at MS stage. Application of nitrogen fertilizer significantly improved N content of cassava. However, phosphate and potassium fertilizers had little impact on N content. Phosphate fertilizer only significantly improved P₂O₅ content at SS stage while nitrogen and potassium fertilizer also enhanced P₂O₅ content. The application of potassium fertilizer significantly increased K₂O content of cassava, whereas nitrogen and phosphate fertilizers had no effect on K₂O content. The effects of nitrogen and phosphate fertilizers on N and P2O5 contents of 'SC205' were similar to those of 'SC5'. However, potassium fertilizer improved K₂O content of 'SC205' more than that of 'SC5'. While N and P₂O₅ contents of 'SC205' were very close to that of 'SC5', N content of 'SC205' at TRF stage was significantly higher than that of 'SC5'. Also P₂O₅ content of 'SC205' was significantly lower than that of 'SC5'.K₂O content of 'SC5' was higher than that of 'SC205' at SS to TRB stages and the difference was notable at TRF and TRG stages. It was concluded that N, P₂O₅ and K₂O contents of different cassava varieties were different, which significantly influenced cassava yield. Therefore to fertilize cassava, it was necessary consider not only nitrogen, phosphate and potassium fertilizer balance but also the nutritive characteristics of different cassava varieties.