Cultural, manurial and water requirements for sweet potato (Iponoea batatas (L) Lam.)

Abstract

Three field experiments were conducted in the wet lands and garden lands of Instructional farm of College of Agriculture, Vellayani to work out cultural, manurial and water requirements for sweet potato. The treatments in the first experiment – Nutritional requirements of sweet potato – consisted of three level of nitrogen (50, 70 and 100kg N/ha), three levels of phosphorus (25, 50 and 75kg P2O5/ha) and three levels of potassium (50, 75 and 100kg K2O/ha). The experiment was laid out in a 33 partially confounded factorial design with two replications. The second experiment – spacing cum depth of application of fertilizers – consisted of three spacing (40cm x 20cm, 60cm x 20cm and 80cm x 20cm) and three depths of application of fertilizers (10cm, 20cm and 30cm). The experiment was laid out in a 32 factorial design in RBD with four replications. The third experiment – Irrigation requirement – consisted of four levels of irrigation (IW/CPE ratios 0.25, 0.50, 0.75 and 1.00) and four levels of fertilizers (50:25:50, 75:50:75, 100:75:100 and 125:100:125 kg N,P and k/ha). The experiment was laid out in a split plot design with five replications. In the experiment to study the nutritional requirement of sweet potato growth attributes like length of vine, number of branches and leaf area index were maximum at higher levels of nitrogen and potassium. The highest values of tuber number, tuber weight, length of tuber and girth of tuber were obtained by the application of 75kg N, 50kg P2O5 and 100kg K2O/ha. Application of nitrogen, phosphorus and potassium at the rate of 75:50:100 kg/ha was found to be optimum for higher tuber yield. While nitrogen nutrition increased the protein content of tuber, potassium application enhanced the starch content. Highest levels of nitrogen, phosphorus and potassium increased the leaf, stem and tuber dry matter production and tuber bulking rate. Potassium only did influence the net assimilation rate. Crop growth rate was maximum at higher levels of nitrogen, phosphorus and potassium. The plant uptake of nitrogen, phosphorus and potassium was maximum at the highest level of these nutrients. The NPK combination of 75kg N, 50kg P2O5 and 100kg K2O/ha resulted in the maximum net return. Experiment on spacing cum depth of application of fertilizers revealed that wider spacing of 80cm x 20cm enhanced the growth characters such as length of vine, number of branches and LAI. Depth of application was not influential on this aspect. Yield attributes like tuber number, tuber weight and girth of tuber were higher at the spacing of 40cm x 20cm but length of tuber was maximum under wider spacing. Application of fertilizers at 20cm depth recorded maximum values for the aforesaid characters. Closer spacing of 40cm x 20cm and 20cm deep placement of fertilizers recorded higher tuber yield. Among the quality attributes protein content alone was influenced by wiser spacing, but protein and starch contents were increased when fertilizers were applied at 20cm depth. Wider spacing increased leaf and stem dry matter and CGR while closer spacing recorded higher tuber dry matter, tuber bulking rate and net assimilation rate. Depth of application of fertilizers did not influence the dry matter production. Plant uptake of nitrogen, phosphorus and potassium was increased by wider spacing and by the application of fertilizers at a depth of 20cm. A combination of 40cm x 20cm spacing and 20cm deep fertilizer placement resulted in maximum net return. Experiment on irrigation requirements divulged that highest IW/CPE ratio and higher fertilizer combinations recorded maximum length of vine and LAI, but number of branches was not influenced by them. Number of tubers, weight of tubers, length of tubers and girth of tubers were not influenced by irrigation, while levels of fertilizers increased the length of tubers. Tuber yield was higher at IW/CPE ratio of 0.75. Fertilizer combination of 100:75:100 kg of N, P and k/ha produced the maximum yield. Starch and protein contents were increased at higher levels of irrigation and fertilizer application. Total dry matter production and bulking rate increased upto an IW/CPE ratio of 0.75 and upto a fertilizer lever of 100:75:100 kg N, P and k/ha. Plant uptake of nitrogen, phosphorus and potassium at harvest was maximum at higher levels of irrigation and fertilizer application. Irrigating the field when the IW/CPE ratio becomes 0.75 and application of fertilizers at a ratio of 100:75:100 kg N, P and k/ha recorded maximum net returns.