Potential, quality and quantity assessment of sesame plant residue in dry land vertisols of Tigrai, Ethiopia; Approach for sustainability of dry-land farming

In dryland areas, the increasing demand for sustainable production needs to effectively utilize and manage residue. The aim of this study was to evaluate the potential, quality, and quantity assessment of sesame residue in dryland areas. Quantification of residue potential was performed at <650, 650–850, 850–1050, and >1050 m elevation by summing the weight of stack, standing residue, and straw. Whereas, assessment in the residues nutrient content was performed at <650, 650–850, 850–1050, and >1050 m elevation and age of residue (fresh and old). The TN, S and P in the residue were determined by Kjeldahl digestion Method, wet acid digestion Method, and two percent acetic acid (CH3COOH) as extracting to extract PO₄ respectively. Atomic absorption spectrophotometer was used to determine micronutrient cations such as Fe, Zn, and Cu. B was determined by extraction using a mixture of hydrochloric (HCl) and hydrofluoric (HF) acids to plant tissue digests. The nutrient potential was calculated by multiplying nutrient content in residue with the amount of residue estimated ha⁻¹. R software (R version 3.5.2) was used to analyze the data. The result indicates that during the last 20 years, the total cultivated land size covered by sesame was 170,000 (ha) and total grain yield of 0.09 Mt. This implies that the size of cultivated land put under sesame cultivation has increased by 79.5%. On average 2.01 t ha⁻ ¹ of residue was produced annually and about 0.34 Mt yr⁻¹ of residue was harvested from sesame production. The age of residue differed significantly (p <0.05) on TN, S, P, Zn, Fe, Cu, and B content of sesame residue. Nutrient content in residue was ranged from 34.55–24.53 g TN/kg, 9.6–4.2 g S/kg, 5.2–4.3 g P/kg, 23–14.6 mg Zn/kg, 130.23–94.78 mg Fe/kg, 17–6.2 mg Cu/kg and 10.67–9.12 mg B/kg during fresh and old residue analysis respectively. Elevation differed significantly (p <0.05) for TN, S, P, Zn, and Fe. Nutrient content in residue was ranged from 27.1–32.2 g TN/kg, 6–8.5 g S/kg, 6.6–4.1 g P/kg, 20.8–17 mg Zn/kg, 109–116 mg Fe/kg, 12.9–10.4 mg Cu/kg and 10.1–9.6 mg B/kg for the elevation range of <650 m and >1050 m respectively. The TN, S, P, Zn, Fe, Cu, and B potentially produced from sesame residue were in the range of 49.4–69.6 kg N ha⁻¹, 8.5–19.3 kg S ha⁻¹, 8.7–10.5 kg P ha⁻¹, 294–463 mg Zn ha⁻¹, 1.99–2.62 g Fe ha⁻¹, 125–342 mg Cu ha⁻¹ and 183–214 mg B ha⁻¹ respectively. This study clearly concludes that fresh and old residue as well as elevation are critical factors that need to be considered for exploring crop residue and its nutrient potential, quality, and quantity aspects in dryland farming systems.