Phosphorus fractions affected by lime and green manure application in Nitisols of Banja district, northwestern Ethiopia

Low phosphorus (P) availability due to its fixation by iron and aluminum oxides is one of the critical constraints for crop production in acidic soils. Understanding its transformation following application of different amendments is therefore important for better soil management and optimizing P-use efficiency by plants. A two-season experiment was conducted to evaluate the P fractions after integrated application of green manure and lime on faba bean (Vicia faba L.) crops in the Nitisol of Banja district, northwestern Ethiopia. The experiment consisted of ten treatments arranged in a randomized complete block design with three replications. The treatments were T1 (0.1tha − 1 NPS fertilizer); T2 (green manure + 0.1ha − 1 NPS; T3 (4.4 tha − 1 lime + 0.1 tha − 1 NPS); T4 (green manure + 0.05 tha − 1 NPS); T5 (green manure + 1.1 tha − 1 lime + 0.025 tha − 1 NPS); T6 (green manure + 1.1 tha − 1 lime + 0.05 tha − 1 NPS); T7 (green manure + 1.1 tha − 1 lime + 0.1 tha − 1 NPS); T8 (green manure + 2.2 tha − 1 lime + 0.025 tha − 1 NPS); T9 (green manure + 2.2 tha − 1 lime + 0.05 tha − 1 NPS); T10 (green manure + 2.2 tha − 1 lime + 0.1 tha − 1 NPS). Soil samples were taken before planting and after crop harvest for P fraction analysis. A sequential extraction method was used to determine the P fractions. The results revealed that Fe-P (15.94%) was the dominant inorganic P fraction followed by Al-P (10.75%), and Sol -P (2.34%) was the lowest P fraction in the area. Integrated application of green manure, 2.2 tha − 1 lime, and 0.1 tha − 1 NPS fertilizer significantly ( P ≤ 0.05) improved soil pH, available P, Sol-P, Ca-P, and Res-P by 1.2units, 62.4%, 75.3%, 41.9% and 34.2% respectively, and decreased Fe-P and Al-P by 43.6% and 37.7% respectively compared to the sole application of inorganic fertilizer. Integrated application of green manure and 2.2 tha − 1 lime is therefore suggested as a good option to improve the bioavailability of P on the acidic soils of the area.