EFFECT OF TUBER PLANTING DEPTH AND NITROGEN RATE ON YIELD AND YIELD RELATED TRAITS OF POTATO (Solanum tuberosum L.) AT HARAMAYA AND HIRNA, EASTERN ETHIOPIA

Abstract

The field experiment was conducted during 2015 main rainy season, at two locations, Haramaya University Rare research field and Hirna Research field to assess the effect of tuber planting depth and nitrogen fertilizer rate on the yield and yield related traits of potato. The experimental treatments were factorial combinations of four tuber planting depth (5, 10, 15, 20 cm) and five rates of N (0, 46, 92, 138 and 184 kg N kg ha-1), laid out as a Randomized Complete Block Design (RCBD) with three replications. Urea and TSP were used as nutrient sources and an improved variety of potato named Bubu was used as a planting material. The results of the experiment revealed that the main effect of tuber planting depth had significant effect total tuber yield, tuber number of per hill, mean tuber weight, marketable tuber yield, unmarketable tuber yield and percentage of small and large sized tubers, shoot fresh biomass and total dry matter at Haramaya. However, tuber planting depth had no significant effect on plant height, dry shoot biomass, medium sized tuber, specific gravity and starch content of tuber. Similarly, nitrogen had main effect on number of stem, total dry matter, unmarketable tuber yield and percentage of small and medium sized tuber, specific gravity and starch content of tubers. In contrast to this, nitrogen had no main significant effect on plant height, shoot fresh biomass, dry shoot matter, tuber number per hill, mean tuber weight, marketable tuber yield, total tuber yield and percentage of large sized tuber at same location. In addition, tuber planting depth had main effect on plant height, tuber number per hill, marketable tuber yield, unmarketable tuber yield, total tuber yield, percentage of small sized tuber and starch content tuber at Hirna. However, this factor had no significant main effect on number of stem, shoot fresh biomass, total dry matter, total dry biomass, mean tuber weight, and percentage of small, medium and large sized tuber at same location. Nitrogen had significant main effect on shoot fresh biomass, dry shoot matter and unmarketable tuber yield while the rest parameters showed non-significant effect. Tuber planting depth and nitrogen application rate had significant effect on unmarketable tuber yield, whereas, all other parameters recorded non significant interaction effect at Haramaya. Tuber planting depth and nitrogen application rate had significant effect on unmarketable tuber yield, and percentage of medium and large sized tubers, specific gravity and starch content of tubers while all the rest parameters showed non-significant interaction effect in case of Hirna. The highest total marketable tuber yield (26.26 ton ha-1) were recorded from a planting depth of 15 cm and the lowest total marketable tuber XI yield (20.33 ton ha-1) were observed from a planting depth of 5 cm. Total tuber yield was highest at 10 cm depth and decreased in both directions, below and above 10 cm depth. However, the combination of tuber planting depth and nitrogen application showed no significant difference at both locations. Thus, the maximum total tuber yield recorded from 10 cm depth was 26.93 and 34.57 t ha-1 at Haramaya and Hirna respectively. At Haramaya tuber planting depth of 10 cm exceeded 5 and 15 cm by about 17.65 and 0.15%, respectively. Tuber planting depth of 10 exceeded 5 and 15 cm depth by about 32.3 and 12.17%, respectively at Hirna. Potato responded well to the tuber planting depth (5, 10, 15 and 20 cm) in terms of growth and yield in the study areas. Therefore, small holder farmers and other potato growers in the area could be advised to use tuber planting depth of 10 cm to optimize potato tuber yield. However, it is premature to come up with a conclusive recommendation since the experiment was conducted for one season only.