INTEGRATED EFFECTS OF VERMICOMPOST AND NPS FERTILIZER ON SELECTED SOIL PHYSICOCHEMICAL PROPERTIES AND YIELD AND YIELD COMPONENTS OF ONION CROPS IN MESKAN WOREDA, EAST GURAGE ZONE, CENTRAL ETHIOPIA.

Abstract

The reduction in soil fertility caused by nutrient depletion poses a significant challenge for lowinput crop production across many regions of Ethiopia. Onion (Allium cepa L.) exhibits a notable response to the application of NPS and vermin compost (VC) fertilizers. However, the optimal dosage of these fertilizers has yet to be determined in the study area. Additionally, there is limited understanding of their impact on soil properties and onion yield, primarily due to the low usage rates of both organic and mineral fertilizers by local farmers. Consequently, this study aims to examine the effects of combining vermin compost with NPS fertilizer on the physicochemical properties of the soil, as well as the yield and yield components of onion (Allium cepa L.). The research was conducted in the Dobbi Kebele of the East Gurage Zone, under irrigated conditions. The experimental design included factorial combinations of five NPS rates (0, 100, 200, 300, and 400 kg NPS ha-1 ) and three vermicompost rates (0, 2.5, and 5 tons ha-1 ), arranged in a randomized complete block design (RCBD) with three replications. Soil samples were analyzed for texture, bulk density, pH, total nitrogen, available phosphorus, sulfur, organic carbon, cation exchange capacity, organic matter, and exchangeable bases (calcium, magnesium, potassium, and sodium). The yield and its components were also assessed. The results from the soil analysis conducted from before and after crop harvest indicated that the application of vermicompost significantly (p available phosphorus (from 4.86 to 10.77), available sulfur (from 35.99 to 52.94),cation exchange capacity (from 37.98 to 78.68), and exchangeable potassium (from 0.55 to 1.64). These analyses were performed using SAS software version 9.4, employing analysis of variance. The study demonstrated that the application rates of NPS and VC, along with their interaction, had an impact on various phonological and yield parameters of onion crops. Specifically, factors such as neck thickness of the bulb (cm), the interaction of NPS and VC on days to maturity, and bulb length (cm) were favored, while the effect of NPS fertilizer on bulb length was found to be non-significant. Both fertilizers and their interaction influenced all selected physical and chemical properties of the soil following the harvest of onion crops. Notably, the highest marketable bulb yield (32.78 ton ha-1 ) and total bulb yield (33.33 ton ha-1 ) were recorded from the combination of 400 kg NPS ha-1 with 5 ton VC ha-1 . The largest bulb diameter (7 cm) and the highest average bulb weight (120 g) were also achieved with this interaction. The application of 100-400 kg NPS ha-1 combined with 2.5-5 ton of VC ha-1 resulted increases in organic carbon, total nitrogen, available potassium, available phosphorus, and cation exchange capacity compared to the control treatment. Consequently, it is concluded and recommended that the application of 5 ton VC ha-1 in conjunction with 400 kg of NPS ha-1 enhances soil physicochemical properties and onion crop yields in Meskan Woreda, East Gurage Zone. The highest marginal rate of return (MRR%) of 10855% was observed for plots receiving 100 kg NPS ha-1with 2.5 ton VC Ha-1 , while the highest adjusted marketable bulb yield of 32.78 ton ha-1 , along with the greatest net benefit and benefit-to-cost ratio of 1,204,612 Birr ha-1 and 108.55 Birr ha-1 , respectively, were recorded for plots treated with 400 kg NPS ha-1 combined with 5 ton of vermicompost for the production of Bombay red onions in Meskan Woreda.