Effects of nitrogen and plant density on yield and quality of sweet potatoes

Abstract

A field experiment was laid out to investigate the effect of nitrogen levels (0, 45, 90 Kg Nlha) and plant density at (4l600plantslha) and (83200 plantlha) on production of vines and storage roots in the variety Helena. The experiment was conducted during two seasons using a factorial design, during each season vines were harvested at 90, 140 and 190 Days after planting (OAF). Storage roots were harvested and weighed at the end of each season. Crude protein and crude fibre content of the vines was determined by proximate analysis. Results during the first season showed an effect of the interaction nitrogen X density on vine fresh weight yields at 90, 140 OAP and total vine fresh weight. Planting at high density and fertiliser at 90 KgN/ha increased vine fresh weight to a maximum of 14tJha and total vine fresh weight at the three harvesting intervals to 33.7tJha. In the second cropping season, at 190 OAP, high density and 45KgN/ha increased vine dry matter yields from 0.1 to OAtiha compared to no nitrogen application. Density, nitrogen and their interaction had no effect on the vine dry matter yields at 90, 140 OAF and total vine dry matter yields. High density increased storage root yields with application of 90KgN/ha during the first season. There was no effect of nitrogen, or the interaction. In the second cropping season there was no response to nitrogen, density or their interaction. Yield of storage roots was higher during the first season than the second season at all nitrogen levels. Across all nitrogen levels, crude fibre was higher at 190 than 140 OAF during the first season at both normal and high density and at normal density during the second season. Crude fibre content increased with increasing nitrogen rate at 190 and 140 DAF at high density during the first and second seasons respectively. During the first season, crude protein was not different for all nitrogen levels at the normal density. At the high density, crude protein decreased with increase in nitrogen levels at both 140 and 190 OAF. In the second season, crude protein content decreased with increase in nitrogen levels at 140 DAF at normal plant density. At high plant density, crude protein reached a maximum of 20.1% at 140 DAF when viii 45KgN/ha was applied. However at 190 OAP, crude protein reached a maximum of 23.0% when 90KgNiha was used at high density. Generally, the experiment showed that density and the interaction density X nitrogen increased the storage roots, fresh vine and dry matter yields during the dry season. Higher storage roots, fresh vine, dry matter yields, crude protein and fibre were recorded in the wet season. Nitrogen had no effect on the measured parameters. This means that higher yield of both fresh roots and vines for human and livestock can be achieved by balancing plant density and time of harvesting of dual-purpose sweet potato Helena.