ASSESSMENT AND MAPPING OF THE STATUS OF MICRONUTRIENTS IN THE SOIL AND TEF [Eragrostis tef (Zucc.) Trotter] LEAF AND GRAIN AT ADA’A DISTRICT, ETHIOPIA

Abstract

The sub optimal fertilizer use and unbalanced fertilizer applications has led to a decline in soil productivity and low response of tef to N and P fertilizers, which might be due to insufficiency of micronutrients in the soil. This study was initiated to investigate and map the status of micronutrients in soil and tef grown on Vertisols of Ada’a district. A total of sixty composite samples for each of soil, tef leaf and grain were collected from twenty georeferenced tef fields of five randomly selected kebeles. The soil samples were analysed and following standard procedures and analysis of variance were employed to separate the means. All of the analyzed soil properties as well as nutrients concentration in tef varied significantly (P < 0.01) among the study sites except clay and silt fractions of soil and Fe concentration in tef grain. The study area was clayey in texture, neutral to slightly alkaline in soil pH (6.87 - 7.93) and low to medium in OM (1.87 and 3.03 %) with lower TN (0.03 % to 0.14 %). Av.P (2.01 - 14.51 mg kg-1) and S (1.80 - 3.41 mg kg-1). Higher concentrations of exchangeable Ca (12.70 - 54.60 cmol(+) kg-1), Mg (2.80 - 16.10 cmol(+) kg-1) and K (1.00 - 2.30 cmol(+) kg-1), but lower Na (0.10 - 0.20 cmol(+) kg-1) content were recorded. Soil of the district had higher levels of CEC (30.30 to 55.40 cmol(+) kg-1) and lower CaCO3 (1.80 to 2.80%) content. The soil had adequate levels of DTPA extractable soil Mn (11.15 - 24.61 mg kg-1) and Zn (1.00 - 2.75 mg kg-1), whereas deficiency of Fe (0.57 - 2.92 mg kg-1), Cu (0.36 - 2.59 mg kg-1) and B (0.06 - 0.26 mg kg-1) in 80%, 95% and 100% of soil samples, respectively. The total forms of soil Fe (1094.76 - 2569.61 mg kg-1), Zn (51.52 - 59.73 mg kg-1) and Cu (2.70 - 13.17 mg kg-1) were in their sufficient range. However, 35% of the samples were lower in total Mn (901.87 - 1488.00 mg kg-1) content. Tef leaf had sufficient concentrations of Fe (114.70 - 2911.50 mg kg-1), Zn (19.60 - 53.10 mg kg-1) and Cu (4.20 - 39.20 mg kg-1), whereas 65% and 35% of leaf samples were lower in Mn (27.50 - 83.20 mg kg-1) and B (2.00 - 67.90 mg kg-1) concentrations, respectively. Tef grain had lower concentrations of Fe (7.50 - 43.20 mg/100g), Cu (0.75 - 1.72 mg/100g) and B (0.20 - 0.40 mg/100g), whereas higher Mn (5.20 - 15.80 mg/100g) and Zn (1.90 - 5.00 mg/100g) were recorded. The soil extractable Mn (r = 0.43*), contents was positively correlated with the concentration of Mn in tef leaf. The soil extractable Zn (r = 0.50*) had a positive correlation with the concentration of Zn in tef grain. In summary, the contents of micronutrients in soil, tef leaf and grain samples including the total soil micronutrients content were found to be lower, which indicates the depletion of soil nutrients through time. The sufficiency of Mn and Zn as well as deficiency of Fe, Cu and B partly reflected both in the soil and tef samples. These results implies that fertilizers containing Fe, Cu and B need to be applied by conducting further experiments under green house and field conditions considering improved soil management practices for water logging to replenish the deficient micronutrients for sustainable crop production in the area. Moreover, plant samples can be good indicators of micronutrients status in the soil and there is a need for establishing micronutrients sufficiency levels in tef leaf and grain.