Effects Of Rate And Stage Of Potassium Application On Yield And Starch Accumulation Of Cassava

To study the effects of potassium (K) application rate and stage on the starch accumulation and the activity of associated enzymes in the root tuber of cassava(Maninot esculenta crantz.). field experiments were conducted with Xin Xuan 048 during 2013-2014 in the experimental filed Agricultural College of Guangxi University. We set three potassium application rates (Al:K2O 450 kg/hm2、A2:K2O 300 kg/hm2、A3:K2O 150 kg/hm2 and CK:K2O 0 kg/hm2) and three different potassium application stages (B1:the potassium was applied all at once as base fertilizer, B2:the potassium was used at Seeding stage at one time, B3:the potassium was used as Tuber fertilizer at one time). According to the experiments, we found that:1 Potassium can accelerate the stem elongation and stem diameter of cassava, and this kind of acceleration is more distinct during the midanaphase of growth. The A1B1 and A2B2 treatment have a good regulation on the growth of stem and leaves in the life of cassava.2 Potassium suppresses the accumulation of chlorophyll in the early stage of growth, but it can obviously promote chlorophyll accumulation during the middle and late period. In the midanaphase of growth, the chlorophyll accumulation decreases gradually as A2>A3>A1; under the same potassium pattern; and under the same potassium rate, the tendency shows as B2>B3>B1. Potassium application can increase protein accumulation to some degree, especially during the early-bulging period. We found that potassium application have no obvious effect on net photosynthesis rate when the cassava are in the early stage of growth, but did accelerate leaf net photosynthesis rate during midanaphase, among which the A2 treatment performs best.3 In the seeding stage, potassium application have no obvious contribution to the rate of total soluble sugar in the leaves, but it increases the sucrose accumulation in the leaves and stems; in the tuber formation stage, potassium decreases the total soluble sugar rate in the leaves and stems, and sucrose rate also decreases in the stems and tuber when potassium was used during the tuber formation stage, while total soluble sugar in the tuber increased. In the tuber bulging stage, potassium employment can increase the rate of sucrose in different organs to some degree; In the maturity stage, potassium application promotes the total soluble sugar in the leaves, but represses sugar accumulation in the stems and tubers. A1 treatment performs better in increasing the supply of sucrose, the substrate of starch synthesis, and the rate of starch accumulation, so as to increase the starch yield.4 Potassium employment can increase the rate of total sucrose, amylopectin and amylocellulose, especially the treatment A1B1,which the effect seems much more obvious. In the tuber formation stage, K. mostly improves the Starch Debranching Enzyme (DBE) activity in the tuber, and the A1B2 treatment shows the highest DBE activity.In the early stage of bulging, K application mainly increases the activities of AGPase (ADP-glucose pyrophosphorylase, AGPase), SSS (Solubal Starch Synthase, SSS), SBE (Starch branching enzyme, SBE) and DBE, and these four enzymes show high activity under the A2B3 treatment. In the middle-bulging stage, K promotes the activities of SSS, SBE and DBE, among which DBE activity increased most dramatically, and A3B2 treatment more conducive to improve the activity of DBE. In the maturity stage, K application increases the activities of SSS and DBE, and SSS activity enhanced most obviously, B2 treatment shows a high SSS activity.5 Potassium application can increase the rate of Quick-acting potassium in the soil.In the seeding stage, A1B2 treatment distinctly increased the rate of Quick-acting potassium in the soil, which increased by 101.99% when compared with CK control. In the tuber formation and early-bulging stage, under the A1B3 treatment, the soil shows the highest quick-acting potassium rate, which increased by 353.47% when compared with CK treatment. In the middle-bulging and maturity stage, A1B1 treatment performs best in increasing the quick-acting potassium rate, which increased by 155.95% when compared with CK control. Also, potassium employment can increase the available nitrogen rate evidently in the maturity stage. A1B3 treatment can remarkably increase the available phosphorous rate in the soil, A2B2 treatment trends to remarkably increase the rate of organic matter in the soil.6 In the early stage of growth, K application mainly improves total potassium rate in the tuber. In the middle to late stage of growth, K application can increase the rate of total potassium in leaves, stems and tubers, Among all the treatments, A3 Bl performs best in increasing total potassium in the tuber, while A2B3 treatment contributes to increase total potassium in the leaves remarkably.7 Potassium employment can increase the length and weight of cassava tuber, and can also increase the yield of tuber and starch, A2B2 treatment led to the highest yield. When the potassium application (K2O) was 150 kg/hm2-300 kg/hm2, under the pattern of B1 and B2, the cassava root yield and starch yield increased with increasing quantity of K. under the pattern of B3, the root yield decreases with increasing quantity of K. When the amount of K2O was 300kg/hm2-450 kg/hm2, the results of B1 and B2 seems to be the same as the case of 150 kg/hm2～300 kg/hm2 and B3.And in this case, B3 treatment does not increase the root yield, in the contrary, the root yield decreases with increasing amount of K, while the starch content does increase with increasing quantity of potassium.