Effects of different N, P and K treatments on absorption and  accumulation  of nutrients and yield of cassava

【Objectives】Cassava (Manihot esculenta Crantz) is one of the most important calorie-producing crops in tropics and subtropics, and mainly used for processing industrial food, forage. N, P and K significantly affect Cassava yield, but the study on nutrient accumulation in cassava at different stages and on biomass as well as yield formation is still limited. In this paper，the biomass and accumulation of nitrogen, phosphorus and potassium were investigated under different fertilizers treatments, and we also explored the accumulation characteristic of nitrogen, phosphorus and potassium in cassava at different growth stages.【Methods】SC205 cultivated widely in south China was used as test material in this experiment. Field fertilization trials with CK (no fertilizer), PK, NK, NP and NPK treatments were carried out at a hilly slope land in Yunan city Guangdong province in 2009. The dry matter and the contents of N, P2O5 andK2O in cassava SC205 were examined respectively at the seedling stage (SS), tuber root formative stage (TRF), tuberous root early growing stage (TRG), tuberous root rapidly bulking stage (TRB) and maturity stage (MS), and analysis on cumulative dynamics and principal component of N,P2O5 andK2O were carried out using N,P2O5 andK2O content and accumulations as original variables at each stage to find out the importance of N,P2O5 andK2O content and accumulations at each growth stage, and to analyze influence of different fertilizer combination on N,P2O5 andK2O content and accumulations at each stage.【Results】The results showed that the biomass accumulation curve of SC205 is exhibited in S shape, and the biomass at SS was relatively low, and increased rapidly after TRF, but the increase trend slowly declined at MS. Nitrogen fertilizer had the greatest influence on the biomass, the second factor was potash, the influence from phosphate is the least. Data also showed that N content in SC205 was ranged from 3.99% to 0.93%, and the content of P2O5was ranged from 0.82% to 0.26%, and the content ofK2O was ranged from 1.39% to 0.89%. The contents of N,P2O5 andK2O at SS reached the highest values, and decreased with the extension of plants growth, especially in N content. Study proved that different fertilizer treatments significantly affect the contents of N,P2O5 andK2O in cassava. Compared with NPK treatment, N content in the PK treatment reduced by 32.96%, and the content ofP2O5 in the NK treatment reduced by 16.21%, and the content ofK2O in the NP treatment reduced by 50.37%. Analysis of principal components showed that the accumulation amounts of N,P2O5 andK2O were significantly associated with cassava production, and that the nutritional status was significantly related to the N content at TRF,K2O content at SS andP2O5 content at TRB. Detection on nutrients showed that accumulation of N,P2O5 andK2O increased with cassava growth and development. N accumulation is greater at TRF, TRG and TRB,P2O5 accumulation is greater at TRF and TRB, whileK2O accumulation is higher at TRG, TRB and MS, and accumulation of N,P2O5 andK2O at TRB significantly influenced the total cumulative nutrients . Meanwhile, N andK2O accumulation at SS and at TRF impacted the total cumulative nutrients as well.【Conclusions】Plant growth changed the contents of N,P2O5 andK2O contents at different stages, but the accumulation of N,P2O5 and K2O increased. Different ratios of N, P, K fertilizers could remarkably affect the cassava biomass, the nutrient contents, the nutrient accumulation, the production and quality of cassava, and the most important factor is nitrogen fertilizer, the second factor is potash, the influence from phosphate is the lowest, showing that SS, TRF and TRG could be the optimum periods for N and P fertilizer application, and TRF, TRG and TRB could be the optimum periods for K fertilizer application.