Abstract:
The morphological, physical and chemical properties of soils in Lay Gayint district have never been studied and scientifically classified to provide soil resource information. Besides, the area receives high amount of annual rainfall, and the soils develop acidity which is a critical issue requiring urgent attention in most highlands of Ethiopia due to its impact on crop production and productivity. Therefore, characterization and classification of soils in Yikalo subwatershed of Lay Gayint district could provide soil resource information. Furthermore, application of organic and inorganic amendments could effectively reduce soil acidity, and improve soil fertility. Four experiments were conducted in the field, laboratory and greenhouse conditions. Soil survey and characterization covered an area of 2294 ha divided into four slope positions, namely: upper, middle, lower and toe slope positions. Representative soil pedons were opened from each slope position and described on genetic horizon basis in the field for their morphological characteristics and analyzed in the laboratory for physical and chemical soil properties. The results revealed the presence of variations in the selected morphological properties within a pedon and along the topographic positions. Soils differed in reaction from 4.57 to 6.42. On the surface horizons of the soil pedons, OC (organic carbon) content ranged from 0.90 to 5.60%, TN (total nitrogen) varied from 0.34 to 0.14%, available P content varied from 0.21 to 3.25 mg kg-1,and exchangeable acidity ranged from 0.17 to 3.65 cmolc kg-1 soil. There was no consistent trend for CEC and PBS with soil depth and topographic positions. The soils in Yikalo Subwatershed were classified as Hyperdystric Cambisols (Humic), Haplic Alisols (Humic), Cambic Umbrisols (Colluvic), Haplic Luvisols (Epidystric), and Pellic Vertisols (Mesotrophic). The incubation and pot experiments were arranged in a completely randomized design (CRD) with three replications. The treatments comprised sole and systematically combined applications of lime, mineral P, compost, and FYM. The result indicated that various treatment combinations raised the soil pH significantly at the 40 days of incubation. All the treatments showed increased P availability with increasing time of incubation. Maximum available P was observed at the 60 days of incubation due to application of 8 t FYM ha-1 + 30 kg P ha-1 + 5 t lime ha-1 followed by 8 t compost ha-1 + 30 kg P ha-1 + 5 t lime ha-1. Exchangeable acidity and Al3+ were reduced significantly (P < 0.001) at the 40 and 60 days of incubation with the application of 30 kg P ha-1 + 10 t lime ha-1 followed by 4 t FYM or compost ha-1 + 15 kg P ha-1 + 10 t lime ha-1. The highest exchangeable Ca2+ was obtained at 20 days of incubation with xviii the application of 30 kg P ha-1 + 10 t lime ha-1 followed by 4 t ha-1 FYM + 15 kg P ha-1 + 10 t lime ha-1. Sole addition of 10 t lime ha-1 increased ECEC from 17.59 to 22.09 cmolc kg-1 at the 40 days of incubation. Combined applications of 30 kg P ha-1 + 10 t lime ha-1 followed by 4 t FYM ha-1 + 15 kg P ha-1 + 10 t lime ha-1 improved ECEC of the soil from 17.59 to 23.95 and 22.97 cmolc kg-1, respectively at the 40 days of incubation. Application of 8 t FYM ha-1 + 30 kg P ha-1 + 5 t lime ha-1 produced significantly (P < 0.001) the highest plant height, number of branches and leaves per plant, shoot dry weight, tissue N and P contents and uptakes of faba bean, and soil N and P after harvest. Significant increases in nodule number and nodule dry weight were obtained due to the application of 4 t FYM ha-1 +15 kg P ha-1 + 10 t lime ha-1. In the field, the treatments tested in the greenhouse were verified for their effect on the yield and yield attributes of faba bean. Combined application of 8 t FYM ha-1 + 30 kg P ha-1 + 3.6 t lime ha-1 increased plant height, number of leaves and branches per plant, pod length, biological and straw yields. Grain per pod, grain yield and thousand grain weight were increased due to the application of 4 t FYM ha-1 + 15 kg P ha-1 + 7.2 t lime ha-1. This treatment resulted in 102% grain yield advantage over the control. The next higher grain yield was obtained from the application of 4 t FYM ha-1 +15 kg P ha-1 + 3.6 t lime ha-1. Among the sole treatments applied separately, 8 t FYM ha-1 was superior in all parameters considered followed by 7.2 t lime ha-1. The roles of lime and FYM in correcting soil acidity, and the utilization of P were the principal contributions in improving the growth and yield of faba bean. Therefore, soil management practices such as integrated application of 4 t FYM ha-1 + 15 kg P ha-1 + 3.6 t lime ha-1 could be suggested as effective amendment to improve the yield of faba bean in strongly acid soils while maintaining soil fertility.