Effect of Inorganic Fertilizer and Sowing Methods on Tef (Eragrostistef (Zucc.) Trotter) Production in Ethiopia: Review

Summary Tef [Eragrostistef (Zucc.) Trotter] is one of the major small cereal crops in Ethiopia in terms of production and consumption. But in Ethiopia, it is yield low as compared with other major cereal crops growing due to many production constraints such as low soil fertility, lack of appropriate management practices, minimum use of improved varieties, and lack of location specific fertilizer recommendation. Synthetic fertilizer and sowing method have great role on yield and yield components of Tef. So, objective of this study is to review the effects of inorganic fertilizer and sowing methods on yield and yield components of Tef in Ethiopia. Most research work so far focused on NP requirements of crops, but limited information is available on various sources of fertilizers like S, Zn, B and other. Tef responds differently to fertilizer rates and types depending on soil type and cultivars. Application of other sources of nutrients beyond urea and DAP, especially those containing S, Zn, B and other micro-nutrients and different method of sowing could increase Tef crop production and productivity in different area and different agro ecology. Therefore, to increase the production and productivity of tef in country use of Synthetic fertilizer and row sowing are important.


Effect of Inorganic Fertilizer on Tef production
Different studies in various environments at different years reported that tef responds to inorganic fertilizer. Mitiku (2008) stated that application of 69 kg N ha -1 was the best to obtain high total biomass yield, straw yield and grain yield. Similarly, Legesse (2004) found that, high yield components were recorded in response to application of 69 kg N ha -1 . As applied N rates increased, the grain uptake also increased which was also reflected in the plant height, yield and yield components like panicle length, panicle weight, grain yield, straw yield and biomass yield. The studies carried out at Oromia and Tigray region of Ethiopia showed that application of 69 kg N ha -1 increase grain yield of tef but not significance difference from application of 46 kg N ha -1 at two regions as showed in table 1. Temesgen (2001) also reported that the application of different levels of N fertilizer affected grain, straw and biomass yield significantly on farmer's field where increasing N fertilizer rate consistently increased Tef grain yield from 1620 kg ha -1 in the control treatment to 1950 kg ha -1 in the 69 kg N ha -1 rate was applied.  [Giday et al., 2014;Seifu , 2018.] Mehreteab (2008) reported that panicle length, plant height, number of nodes, number of effective tillers, lodging index, biomass yield, grain yield and harvest index increased with an increased level of phosphate fertilizer and the optimum grain yield was obtained by applying phosphate fertilizer rate of 46 kg P 2 O 5 ha -1 . Bereket et al. (2014) reported that increasing P rate from 46 to 69 kg P2O5 ha -1 increased grain yield of bread wheat by about 6.8%. Alemayehu et al. (2006) indicated that the highest grain yield was obtained with the highest P fertilizer rate (80 kg P2O5 ha -1 ) in most localities of Vertisols and the highest grain yield in most localities of Nitosols were obtained at 60 kg P2O5 ha -1 with interaction of 100 and 60 kg N ha -1 , respectively.
According to Habtegebrial and Singh (2006) found that combined N and S fertilization increased the dry matter and grain yields of tef on average by 1.7 and 0.3 kg ha −1 , compared with the control and S fertilization increased the nitrogen use efficiency of the tef crop by 36%. Mulugeta and Shiferaw (2017) Suggested in Ethiopia application of suboptimal levels of mineral fertilizers aggravates the decline in soil fertility. Application of 150 kg NPS (63:25:10.5) + 34.5 kg N ha -1 gave highest grain yield. Seifu (2018) reported that the highest grain yield (3228 kg ha -1 ) of tef was obtained at the highest rate of blended (150 kg NPSB ha -1 ) fertilizer application, while the lowest grain yield of 2503 kg ha -1 was recorded from non-treated (control) plot.
According to Fayera et al. (2014) the maximum tef grain yield was obtained with the highest total nitrogen, phosphorus, potassium and zinc uptake. Application of blended fertilizer gave maximum tef yield over NP fertilizer. Application of 100 kg NPSZnB ha -1 produced the maximum grain yield (1386.5 kg ha -1 ) of tef, while the lowest grain yield (1085.8 kg ha -1 ) was obtained under the control treatment (Teshome, 2018). Lemlem (2002) also reported that application of blended fertilizer, DAP and urea significantly increased the N, P, K, Zn, Mg and S concentrations tef grains and increased grain yield in Vertisols. Application of blended fertilizer increase tef yield from 12.4 to 39.6 % over the control plots.

Response of Crops to Sowing Method 2.3.1. Broadcasting
Broadcasting as one of the seed sowing methods, and in combination with reduced cultivation offers the advantage of being up to four times faster than conventional ploughing and drilling and is of particular value for sowing large hectare of winter cereals (Ball, 1996). Under the current farmers' production system, Tef seeds are sown on the surface of the soil and left uncovered or sometimes covered very lightly by pulling woody tree branches over the field using oxen (Seyfu ,1997). The broadcasting system with poor quality of seed, poor soil fertility, and seed rate which is 25-50 kg/ha which make the mature plant to lodge i.e. fall over. All these things affected the production of Tef. One of the risks associated with higher plant populations is the increased potential for lodging which can impact yield and quality. This may be particularly true under high yield environments like the Red River Valley (Tareke, 2008).

Row planting
In order to avoid uneven stands, improve tillering, improve yield attributing parameters, to reduce lodging and decrease competition among plants, row sowing is preferred although it is tedious, time taking and needs educated person (Hunt, 1999). Row planting of teff seed is considered to be superior compared to the traditional broadcasting method because a reduced seed rate decreases competition between the seedlings for water and nutrients. Moreover, the even distribution of the teff seedlings makes weeding easier and less costly. In research trials, row planting has been shown to increase teff yields up to three times average yields and lowers seed costs, making it seemingly a good value proposition for teff farmers . According to Tareke (2008) best results came from spacing and row sowing increases tiller number, producing strong and fertile tiller culms, and increase the number of seeds/panicles of Tef.

Transplanting Methods
According to Tareke (2008) planting seedlings on a flat bed and transplanting those into the field showed a promising result. For example, it reduces the seed rate from the broadcasting method and in the new method 2-2.5 kg/ha would be enough for a hectare. Moreover, it increases tiller number, producing strong tiller culms and it increases number and quality of seeds. As the researcher explained, the yield of the broadcasting plot was 500-1200 kg/ha, On the other hand, the transplanted ones gave 3,400-5,100 kg/ha with a fourfold increase in grain yield. In addition, the straw yield also increased from the transplanted grain.

Effects of sowing method on yield and yield components of Tef
It has been argued recently that low Tef productivity is partly caused by the way farmers sow Tef seed. Traditionally, farmers broadcast the seed using a rate of 25-50 kg per hectare. According to ATA (2013a) report most of the farmers who employed new Tef technologies experienced yield increases across all regions. Row planting and transplanting technologies produced especially high yields, on average increasing yields by 70% from the national average of 12.6 quintals/ha to 20.9 quintals/ha. In Amhara and Oromia transplanting produced the highest yields followed by row planting and broadcasting. In SNNP and Tigray row planting produced the highest average yields of 22 and 21 quintals/ha respectively. Transplanting in SNNP and Tigray produced the second highest average yield, with broadcasting producing the lowest in comparison to the other two technologies.  et al., 2016] In Tigray for instance broadcasting yields were 17 quintals/ha, a 30% increase over the national average. As planting method was only one component of the Teff technology package, this increase in yield from broadcasting compared to the national average can be attributed to the other components of the package (ATA,2013a). Broad casting practice reduces yields because of the uneven distribution of the seeds, higher competition between plants for inputs (water, light and nutrients), and difficult weeding once the plants have matured (Fufa et al., 2011) As a solution, it has been proposed to reduce seed rates and to plant seed in rows or to transplant seedlings (as is often done for rice, for example). Reducing the seed rate to between 2.5 and 3 kg per hectare allows for reduced competition between seedlings and optimal tillering of the Tef plants. By row planting or transplanting the seeds, land management and especially weeding can also be done more readily and the incidence of lodging is reduced ). Tareke et al. (2011 reported that transplanting sowing method of tef increased grain yield by increasing productive tillers and reducing lodging. The significant increase in grain yield in response to using transplanting might be attributed due to less competition for growth resource like water, sunlight and nutrients, better air circulation which reduces the occurrence of insect pest and disease infestation and also uniform plant stands given opportunity to suppress weed growth (Wakjira, 2018).

Effects of Inorganic fertilizer and sowing Method on yield and yield components of Tef
Many Authors suggested Synthetic fertilizer and sowing Method on Tef affects yield and yield components of Tef in different way and different area. Shiferaw (2012) reported that application of Blended fertilizer in a row sowing gave (3700-4000 kg/ha) grain yield than the rest of the treatments at different site (Table 4).  [Refissa 2012;Shiferaw, 2012] Significantly lower (830-1500 kg/ha) grain yield was recorded under unfertilized conditions in both broadcast and row sowing at both sites. Application of Blended fertilizer increased grain yield by 102-109% at the two sites as compared to the control treatment (broadcast sowing and non-fertilized). Similarly, Refissa (2012) reported that row sowing method and Blended fertilizer increase tef grain yield than the rest of the treatments at different site (Table 4). Tareke et al. (2012) who reported that transplanting increased grain yield by increasing productive tillers and reducing lodging. Similar results also reported blended fertilizer increased grain yield of tef. Transplanting combined with blended fertilizer increased grain yield by 50% than using DAP or Urea fertilizer, and this increment in grain yield is mainly due to the number of tillers and number of panicles.

Conclusions
Tef is the most widely grown cereals in Ethiopia. It is a staple diet of the majority of the population, and it is most widely planted by Ethiopian farmers and also gaining popularity as a health food in the western world. Ethiopia is the center of origin and diversity of Tef. Ethiopian farmers have been growing Tef for both the grain and straw yeilds. In addition to this, tef is excellently adapted to the changing environments in the country, and thereby suffer low production risks. The principal limitation of Tef cultivation in Ethiopia is the low productivity due to un balanced and sup optimal use of in organic fertilizer and use of broad casting sowing method. Both sowing method and fertilizer types affected yield of tef in Ethiopia. Row sowing reduces seed rate by five times as compared to broadcast sowing and transplanting method reduces seed rate by ten times row sowing method. Application of different nutrient great role in growth, development as well as in yield and yield components of Tef and also nutrient up takes from the soil. Application of different levels of micro primary and secondary nutrients affected growth, yield and yield components of tef. But Ethiopian agriculture has emphasized only on N, P and K-fertilizer inputs. The application of micro element such as Sulfur (S), Zinc (Zn), Boron (B) and others not well known in Ethiopia. The proper application of these micro nutrients with good sowing method has increase yield and yield components of tef. Types of fertilizer whether it is complete or incomplete, macro or micro how it applied, practice sowing method and spacing all this affect the yield and yield components of tef. The best grain yield of Tef can be improved through use of blended in organic fertilizer application and transplant or row sowing method. Therefore, the growers, farmers, researchers and all stakeholders' give attentions in use of blended fertilizers that contain Micro and micro nutrients and sowing methods of tef to increase the yield.