Dry matter production, nitrogen yield and estimation of nitrogen fixation of legumes on vertisols of the Ethiopian highlands

Traditional land management techniques on vertisols frequently lead to soil fertility loss and land degradation. The objective of this study was to evaluate the impact of improved land preparation methods on the dry biomass and nitrogen (N) content of two legume species grown under two phosphorus fertilizer applications. The experimental design employed for these experiments was a randomized complete block design, with six treatments and four replications. Land preparation methods and phosphorus application significantly (P < 0.05) increased biomass production and N content in legumes. Over years and land preparation methods, vetch N accumulation was superior (P < 0.05) to clover and teff (Eragrostis teff). Such a large amount of N accumulation may have a positive contribution to subsequent crops when incorporated into the soil. Land preparation methods and years influenced soil mineral N accumulation, particularly under legumes. The N balance values indicated that it differed among species, land preparation methods, and P treatments over the year. The N balance of vetch +P ranged from 67.1 to 185.9 kg N ha(−1) over years and land preparation methods, whereas the comparable figure for vetch−P was 40.3–141.9 kg N ha(−1). Similarly, the N balance in clover-P ranged from 13.0 to 67.2 kg N ha(−1), and in clover +P from 13.8 to 98.6 kg N ha(−1). Teff's N balance has never exceeded 35 kg ha(−1) over the years.