Potassium critical level in soil for Teff (Eragrostis tef (Zucc.) Trotter) grown in the central highland soils of Ethiopia

Abstract

Responses to potassium (K) fertilizer are reported in different parts of Ethiopia in recent years, contrary to the general perception that K fertilizer was not necessary on the soils. However, use of adequate K level for maximum economic yield is possible only when soil test data are calibrated against response curve for a given crop and soil type. This pot trial was conducted to calibrate K soil test with the response of teff (Eragrostis tef (Zucc.)) at application of increasing levels of K. Random soil samples (0–20 cm) were collected from 60 locations having Mehlich-3 (M-3) K soil test values ranging from 16 to 910 mg kg−1 across 20 teff growing districts in the highlands of Ethiopia. The relative biomass yield of teff was significantly correlated with Mehlich-3 extractable K, suggesting that the extraction method fairly estimated the available soil K. Soil test M-3 extractable K values were categorized, based on relative biomass yield, as “very low” (< 55 mg kg−1), “low” (55–210 mg kg−1), “medium” (210–280 mg kg−1), “high” (280–500 mg kg−1) and “very high” (> 500 mg kg−1). And K application rates of 139 and 54 kg ha−1 for the very low and low K categories respectively would suffice for optimum teff yield. The critical limit of K in soil (M-3) using the graphical method was 210 mg kg−1 for the 85% relative biomass yield level. An inverse relation of yield response to the soil K status was observed suggesting that application of K fertilizer increases yield of teff in low status soils. However, field verification is required to draw sound conclusions.