PRODUCTION PRACTICES OF FABA BEAN (Vicia faba L.) AND RESPONSE OF THE CROP TO APPLICATION OF MINERAL NITROGEN, PHOSPHORUS, AND POTASSIUM FERTILIZERS AND LIME IN ACIDIC SOILS OF WOLAITA ZONE, SOUTHERN ETHIOPIA

Abstract

Faba bean (Vicia faba L.) is one of the major pulse crops grown in the highlands of Wolaita Zone in Ethiopia. However, the production is challenged by soil acidity, low soil fertility, and scarcity of improved varieties. Therefore, three studies (survey, pot and field) were conducted in Wolaita Zone in 2019 and 2020 main cropping seasons with four key objectives:To assess farmers’ soil fertility and faba bean production practices; to identify the optimum liming rate and best varieties to improve faba bean production; to investigate the effect of mineral nitrogen (N), phosphorus (P), and potassium (K) fertilizers on growth, yield components, and yield of faba bean, to determine the optimum mineral N, P, and K fertilizers rate for enhanced uptake and efficient utilization of faba bean in the study area, and to identify the economically best lime and mineral N, P, and K fertilizers for faba bean production in the study area. The first experiment (survey) was conducted on 310 household heads, who were purposively selected based on their faba bean production potential from two districts and six sub-districts in Wolaita Zone. The second (pot) experiment was conducted by using four liming rates (0, 2, 4, and 6 t ha–1 CaCO3) and five faba bean varieties (local, Dosha, Gebelecho, Tumsa, and Bobicho), arranged in randomized complete design (RCD) with six replications. The third and fourth experiments were carried to test the effects of three rates of N (0, 23, and 46 kg N ha–1), three rates of P (0, 46, and 92 kg P2O5 ha–1), and three rates of K (0, 30, 60 kg K2O ha–1) arranged in a randomized a complete block design (RCBD) and replicated three times per treatment. The results of the first study revealed that the soil management practices by farmers were inadequate to improve the soil fertility and enhance faba bean productivity in Wolaita Zone sustainably. Thus, only 27.7%, 32.3%, 3.5%, 1.9%, 36.1%, and 2.9% of the xix sampled farms managed the soil by mineral fertilizers, farmyard manure, liming, faba bean residues management, faba bean rotation, and fallowing, respectively. Consequently, the average grain productions of both fertilized and unfertilized faba bean farms were far less than the national average yield of 2.1 t ha–1. Results from the second experiment showed that crop phenology, growth, yield, and yield components were significantly influenced by the main and interaction effects of liming rates and variety. Accordingly, significantly higher above-ground biomass (23.96 g plant-1) and grain yields (9.58 g plant-1) of the crop were obtained in response to the interaction of Tumsa variety with the application of lime equivalent to 2 t ha–1 lime. The lowest aboveground biomass (16.04 g plant-1) and grain yields (6.42 g plant-1) were obtained in response to the local variety planted with no lime application. Thus, Tumsa variety with 2 t lime ha–1 was identified for field evaluation. The results of the field experiment revealed that the crop phenology, root morphology, growth, yield components, yield, and nutrient uptake and use efficiency of the faba bean responded significantly to the main effect of the year of planting, mineral nitrogen, phosphorus, and potassium fertilizers rates, and their interactions. In this regard, the significantly highest grain yield (4.97 t ha –1) was obtained at 23 kg N-92 kg P2O5-60 kg K2O ha–1 , , which was 360% higher than the yield obtained from the control plots. The results of the fourth experiment (laboratory analysis) revealed that the crop N, P, and, K uptake and utilization indices were significantly responded to the main effect of the year of planting, mineral nitrogen, phosphorus, and potassium fertilizers rates, and their interactions. Accordingly, higher N, P, and, K uptake and utilization indices were obtained from N, P, and, K fertilizers applied at the rate of 23 kg N ha–1, 46 kg P2O5 ha–1, and 30 kg K2O ha–1. Overall, a better grain yield and the highest mean net benefit (163,067.5 ETB ha–1) with an acceptable marginal rate of return (3,987%) was obtained with combined applicationsof 23 kg N-46 kg P2O5-30kg K2Oha–1. Thus, these rates of fertilizers under lime application are suggested for faba bean growing farmers in the acidic soils of Woliata Zone.