Effect of potassium levels on teff (Eragrostis tef (Zucc.) Trotter) growth and yield in Central Highland Vertisols of Ethiopia

Abstract

Nutrient depletion and imbalance are among the major attributes that contribute to declining soil productivity in the highlands of Ethiopia. The blanket fertilizer recommendation, which considered only urea and Di-ammonium phosphate (DAP), was used over the past four decades to improve soil fertility for enhancing crop production. Nevertheless, the average national yields of small cereal including teff were low, despite application of nitrogen and phosphorus (NP) fertilizers. On-farm trials were conducted in the 2015/16 and 2016/17 cropping seasons at 18 locations on Ethiopian highland Vertisols to determine the response of teff to potassium (K) fertilization along with other limiting nutrients. Five K levels (0, 30, 60, 90 and 120 kg ha-1) in the form of murate of potash (KCl) were used in randomized complete block design with three replications. Separate analysis of variance was conducted for each sites and year. Least Significant Difference (LSD) test at P ≤ 0.05 was used to separate means whenever there were significant differences. Analysis of variance revealed a highly significant difference (P < 0.01) between treatments in both straw and grain yields and tissue nitrogen (N) and K concentrations of teff over the twocropping seasons in 67% of the test locations. Additionally, responses to K were obtained on soils with available K test ranging between 166 and 282 mg kg-1. The Ca: K and Mg: K ratios were strongly and negatively correlated with relative yield and the correlations suggest that soil with Ca: K > 50:1 and Mg: K >15:1 are likely to respond to potassium fertilization. The yield advantage accrued due to K application ranged from 30 to 77% in 2015/16 and 8 to 51% in 2016/17 seasons. The economic optimum K fertilizer application rates varied between 60 kg K ha-1 in 44% of the sites to 90 kg K ha-1 in 23% of the sites. The findings highlighted the need for revisiting fertilizer program to enhance the yield and nutrient uptake of teff in K responsive soils and developing critical levels for K in the study sites.

Tef (Eragrostis tef) Responses to Phosphorus and Potassium Fertigation under Semi-Arid Mediterranean Climate

“…Furthermore, maximum yield was observed at a much higher vegetative K concentration in our experiment (1%) compared to the 0.63% K reported by Mulugeta et al [9] as the internal K requirement of tef. It is possible that the decreased grain yield in high K treatments reported by Mulugeta et al [9] was not caused by the increase in K itself, but rather a secondary effect caused by an imbalance of other nutrients. In our experiment, all other nutrients were provided at high rates and in available forms, so imbalances of other nutrients did not occur.…”

“…They reported yield rising and then plateauing with increased K, with a slight, non-significant drop at the highest K level. It is interesting that no decline in grain yield occurred in the higher K treatments, since Mulugeta et al [9] found a decline in grain yield in plants with much lower shoot K concentrations (0.6-0.9%) than the concentrations we measured in the highest K fertilization treatments (Figure 2C). Furthermore, maximum yield was observed at a much higher vegetative K concentration in our experiment (1%) compared to the 0.63% K reported by Mulugeta et al [9] as the internal K requirement of tef.…”

“…It is interesting that no decline in grain yield occurred in the higher K treatments, since Mulugeta et al [9] found a decline in grain yield in plants with much lower shoot K concentrations (0.6-0.9%) than the concentrations we measured in the highest K fertilization treatments (Figure 2C). Furthermore, maximum yield was observed at a much higher vegetative K concentration in our experiment (1%) compared to the 0.63% K reported by Mulugeta et al [9] as the internal K requirement of tef. It is possible that the decreased grain yield in high K treatments reported by Mulugeta et al [9] was not caused by the increase in K itself, but rather a secondary effect caused by an imbalance of other nutrients.…”

“…Although K is universally recognized as important for crop growth and yield, for many years tef grown in Ethiopia was usually fertilized only with N and P and not with K [8]. This was due to the common belief, stemming from studies conducted in the 1960s and 1970s, that claimed that K was not limiting in Ethiopian agricultural soils [8,9]. Recently, this idea was called into question with largescale mapping of Ethiopian soils in a project initiated by the Ethiopian government, called the Ethiopian Soil Information System (Ethiosis) [10].…”

“…Recently, this idea was called into question with largescale mapping of Ethiopian soils in a project initiated by the Ethiopian government, called the Ethiopian Soil Information System (Ethiosis) [10]. A number of field trials have been recently published indicating that K application can increase tef yield [9,11]. Similarly, a greenhouse trial in which different levels of K were applied to tef growing in pots with different Ethiopian soils was conducted in order to determine an optimum K fertilization rate [12].…”