Introduction
Tef (Eragrostis tef [Zucc.] Trotter), a warm-season crop, has a wide adaptation capable of growing in marginal areas, including arid and semi-arid regions of Ethiopia (Gelaw and Qureshi, Reference Gelaw and Qureshi2020) at elevations ranging from sea level to 3,000 m above sea level (Chanyalew et al., Reference Chanyalew, Ferede, Damte, Fikre, Genet, Kebede, Tolossa, Tadele and Assefa2019). The crop is economically essential for smallholder farmers in the country with its high grain and straw market value (Chanyalew et al., Reference Chanyalew, Ferede, Damte, Fikre, Genet, Kebede, Tolossa, Tadele and Assefa2019). In Ethiopia, tef has accounted for 29.3% of the overall area covered under cereals followed by maize (25.6%) in the 2021–22 cropping season (CSA, 2022). Tef is the second most important cash crop next to coffee for smallholder farmers in Ethiopia, generating about half a billion U.S. dollars per year (Abraham, Reference Abraham2015). From value-added tef products in the form of Injera, which is a sour-tasting thin flatbread, Ethiopia had generated up to 10 million U.S. dollars (Fikadu, Wedu and Derseh, Reference Fikadu, Wedu and Derseh2019). In countries such as the United States, South Africa, India, Israel, Yemen, the Netherlands, Germany, Australia, the United Kingdom, and China, tef has been grown as a grain and forage crop in recent years (Barretto et al., Reference Barretto, Buenavista, Rivera, Wang, Prasad and Siliveru2021; Jifar et al., Reference Jifar, Chanyalew, Tadele and Assefa2022). The gluten-free nature of tef grain makes the crop preferred by baking factories and consumers, particularly those with celiac disease, in various European countries (Sridhara et al., Reference Sridhara, Punith Gowda, Manoj and Gopakkali2021). Because of the demand for healthier food, tef-based products are getting a premium price (Barretto et al., Reference Barretto, Buenavista, Rivera, Wang, Prasad and Siliveru2021).
Soil acidity and the decline in organic matter content of the soil are among the main yield-limiting factors in the northwest highlands, which are potential tef growing areas of Ethiopia (Getachew, Reference Getachew2014). Over 40% of the cultivated land in the country is affected by soil acidity, which is even more severe in the study area, where about 45% was found to be moderate to strongly acidic (Asrat, Reference Asrat2020). A non-treated acidic soil of northwestern Ethiopia could provide a 1 t ha−1 grain yield reduction for the tef crop compared to the soil treated with a combination of 1.5 t ha−1 lime and 5 t ha−1 manure (Asrat, Reference Asrat2020). Therefore, treating soil with various soil amendments (SAs) is essential to improve soil physicochemical and biological properties and crop yields in different parts of the country.
Organic and mineral amendments from different sources were used to correct soil properties (Bulluck et al., Reference Bulluck, Brosius, Evanylo and Ristaino2002; Larney and Angers, Reference Larney and Angers2012; Hunegnaw et al., Reference Hunegnaw, Alemayehu, Ayalew and Kassaye2021). However, the type of amendment used varies with the nature and extent of the problem. Organic amendments can restore soil organic matter and microbial contents and maintain plant health (Pérez-Piqueres et al., Reference Pérez-Piqueres, Edel-Hermann, Alabouvette and Steinberg2006; Bonilla et al., Reference Bonilla, Gutiérrez-Barranquero, De Vicente and Cazorla2012). Bioremediation in soils with heavy metal concentration was reported to be provided by those amendments (Park et al., Reference Park, Lamb, Paneerselvam, Choppala, Bolan and Chung2011). The application of compost, biochar, or their combination significantly improved soil water content, organic carbon, cation exchange capacity, pH in the 20 cm surface soil depth, and barley yield (Agegnehu, Nelson and Bird, Reference Agegnehu, Nelson and Bird2016). Crop residue and farmyard manure also improved soil organic carbon content by 2.45% and 6.40%, respectively, compared with mineral fertilizer alone (Blanchet et al., Reference Blanchet, Gavazov, Bragazza and Sinaj2016). However, the efficacy of any organic amendments depends on the chemical composition and quantity added to the soil (Pérez-Piqueres et al., Reference Pérez-Piqueres, Edel-Hermann, Alabouvette and Steinberg2006; Bonilla et al., Reference Bonilla, Gutiérrez-Barranquero, De Vicente and Cazorla2012).
Researchers also reported the importance of inorganic amendments, particularly liming to improve crop yield and soil physicochemical properties in acidic soils. According to Gurmessa (Reference Gurmessa2021), crop yield can be increased by up to 0.5 t ha−1 with the application of lime. Pardo et al. (Reference Pardo, Bernal and Clemente2014) observed that lime application increases soil pH and reduces trace element mobility. Malik et al. (Reference Malik, Yutong, ShengGao, Abassi, Ali, Imran khan, Kamran, Jamil, Al-Wabel and Rizwan2018) also found an improvement in soil pH by 64% with an application of 100% CaO with a 4% sludge biochar. Moreover, DevBehera and Pattanayak (Reference DevBehera and Pattanayak2016) indicated that lime with farmyard manure had improved the Cation Exchange Capacity (CEC) and pH of the soil. Though the SAs play a significant role in improving soil physicochemical properties, their individual and combined effects on the growth and yield of crops, particularly tef, have not been intensively studied.
On the other hand, silicon application had a significant role as an SA and yield improvement by enhancing lodging and disease resistance of various crops such as sugar cane (Majumdar and Prakash, Reference Majumdar and Prakash2020), rice (Singh, Singh and Singh, Reference Singh, Singh and Singh2021), and other monocots, including tef (Ligaba-Osena et al., Reference Ligaba-Osena, Guo, Choi, Limmer, Seyfferth and Hankoua2020). According to Galindo et al. (Reference Galindo, Pagliari, Rodrigues, Fernandes, Boleta, Santini, Jalal, Buzetti, Lavres and Teixeira Filho2021), silicon supply increased the agronomic efficiency of nitrogen fertilization on maize. In addition to the type and rate of silicon application, knowledge of silicon application timing is essential for effective and economical use of the nutrient as it varies with the crop type. For instance, foliar application of silicon was found to improve the root yield and sugar content of sugar beet (Artyszak, Gozdowski and Kucińska, Reference Artyszak, Gozdowski and Kucińska2015), shoot growth and yield, and help to defend against both biotic and abiotic stresses (Zhao et al., Reference Zhao, Yang, Zhang, Zhang, Zhou, Huang, Luo and Luo2022), and whole dose basal application improves grain yield of rice (Singh et al., Reference Singh, Singh, Singh, Singh and Chandel2005). Another research by Rehman et al. (Reference Rehman, Rizwan, Rauf, Ayub, Ali, Qayyum, Waris, Naeem and Sanaullah2019) showed that split application of Si at transplanting, tillering, and panicle initiation stages has improved the growth and reduced cadmium concentrations in rice grain below the threshold level of 0.2 mg kg−1. Moreover, silicon application during the flowering stage as a top dressing increased leaf area, tiller number per plant, panicle weight, 100 seed weight, and stem strength in rice (Dorairaj et al., Reference Dorairaj, Ismail, Sinniah and Tan2020). However, the effect of silicon application and its timing has been poorly documented for tef.
Although tef is an important crop, it has been considered an orphan crop, which has restricted consideration from the global market and mainstream research (Tadele and Hibistu, Reference Tadele and Hibistu2021). The national average productivity (1.7 t ha−1) of tef was far below its genetic potential (Chanyalew et al., Reference Chanyalew, Ferede, Damte, Fikre, Genet, Kebede, Tolossa, Tadele and Assefa2019). Though there are some efforts toward improving the yield of tef, soil acidity, drought, inappropriate nutrient and tillage practices, lodging, and a lack of improved seeds are still among the major factors contributing to the low tef production in Ethiopia (Chanyalew et al., Reference Chanyalew, Ferede, Damte, Fikre, Genet, Kebede, Tolossa, Tadele and Assefa2019). Lodging, which is the permanent displacement of the plants from the upright position, alone could result in an 11%–22% yield reduction in tef crop (Chanyalew et al., Reference Chanyalew, Ferede, Damte, Fikre, Genet, Kebede, Tolossa, Tadele and Assefa2019). The problem is even worse under high nitrogen fertilization (Gebru, Alemayehu and Bitew, Reference Gebru, Alemayehu and Bitew2023). Though lodging is common in most of the monocots, its effect is large due to its genetically thin weak stem compared with other crops. Therefore, high investment cost is needed for research to improve tef productivity, value addition, and promotion to the global market (Tadele and Hibistu, Reference Tadele and Hibistu2021). With the use of improved crop management, the yield of tef can reach up to 2–3 t ha−1 (Tafes Desta, Mekuria and Gezahegn, Reference Tafes Desta, Mekuria and Gezahegn2022).
There are inorganic and organic sources of silicon. Potassium silicate (Gomaa et al., Reference Gomaa, Kandil, El-Dein, Abou-Donia, Ali and Abdelsalam2021), sodium silicate, calcium silicate (Majumdar and Prakash, Reference Majumdar and Prakash2020), and orthosilicic acid (Cuong et al., Reference Cuong, Ullah, Datta and Hanh2017) are among the inorganic sources of silicon for crops. Though they are effective, inorganic silicon sources are costly, not eco-friendly, and less available in the local market (Liang et al., Reference Liang, Nikolic, Bélanger, Gong and Song2015). Therefore, organic sources such as carbonized rice husk (Moayedi et al., Reference Moayedi, Aghel, Nguyen and Rashid2019; Gebru, Alemayehu and Bitew, Reference Gebru, Alemayehu and Bitew2023) and diatomaceous earth with 80% silicon content (Gokavi et al., Reference Gokavi, Jayakumar, Mote and Surendran2021) were found to be alternative silicon sources, which are environmentally sound, relatively inexpensive, and available to smallholder farmers in local markets. The silicon content of carbonized rice husk was estimated in the range of 60%–90% (Shen, Zhao and Shao, Reference Shen, Zhao and Shao2014; Moayedi et al., Reference Moayedi, Aghel, Nguyen and Rashid2019). Hence, integrating locally available and suitable SAs either in the form of carbonized rice husk, organic matter, or lime along with silicon timing would be essential to improve the sustainable productivity of tef and the cultivated land. Therefore, the objective of this experiment was to examine the effect of carbonized rice husk application timing (CRHT) and SAs (carbonized rice husk, organic matter, and lime) on water use efficiency, lodging, and yield attributes of tef at the Koga Irrigation Scheme of northwestern Ethiopia.
Materials and methods
Study site description
This field experiment was conducted at the Koga Irrigation Scheme, Bahir Dar University Research Station (Kudmi), Ethiopia, under irrigation conditions during two offseasons (2021 and 2022). The experimental site is located at 11o23′31″ N to 11o23′32″ N and 37o6′42″ and 37o6′43″ E. The elevation of the study site is 1,983 m above sea level, which falls under mid-land agroecology (CSA, 2012; Gebru, Alemayehu and Bitew, Reference Gebru, Alemayehu and Bitew2023). Based on the historical data (29 years), the area receives a mean annual rainfall of 1,768 mm with a mean maximum and minimum temperature of 27.7oC and 10.7oC, respectively (Gebru, Alemayehu and Bitew, Reference Gebru, Alemayehu and Bitew2023). The monthly distribution of minimum and maximum temperatures and rain for the 2021 and 2022 growing seasons is presented in Fig. 1.
Graphical presentation of mean monthly minimum and maximum temperatures and total monthly rainfall data for the years 2021 and 2022 (*) for Merawi station.
Soil and amendments sampling and analysis
To describe the soil properties of the experimental site before planting, undisturbed and disturbed soil samples were collected from 60 sampling spots over the three different soil layers (0–20, 20–40, and 40–60 cm depth) in a zigzag fashion. The disturbed samples were composited to the respective soil layers with three replications and submitted to the soil and plant analysis laboratory of the College of Agriculture and Environmental Sciences, Bahir Dar University to the analysis of physical properties—bulk density, available water content, and texture—and chemical properties—pH, organic carbon, cation exchange capacity, electrical conductivity, total nitrogen, and available phosphorus content. These were determined using the following methods, respectively: core method (Blake, Reference Blake1965), gravimetric method (Cassel and Nielsen, Reference Cassel and Nielsen1986), hydrometer method (Bouyoucos, Reference Bouyoucos1962), 1:2.5 v/v soil-to-water ratio (Peech, Reference Peech1965), Walkley–Black method (Gelman et al., Reference Gelman, Hill and Yajima2012), ammonium acetate extraction (Mattila and Rajala, Reference Mattila and Rajala2022), 1:5 soil-to-water supernatant solution (Sonmez et al., Reference Sonmez, Buyuktas, Okturen and Citak2008), Kjeldahl method (Bremner, Reference Bremner1996), and colorimetric method (Olsen, Reference Olsen1954).
In addition, samples of compost and carbonized rice husk were prepared and sent to the same laboratory to analyze ash content and other chemical properties. The ash content of compost and carbonized rice husk was determined using the dry-ashing method (Marshall, Reference Marshall2010). The results of the laboratory analysis of the physical and chemical parameters are presented in Tables 1 and 2.
Physical properties of soil over the three layers (0–20, 20–40, and 40–60 cm) during pre-sowing time
Source: Gebru, Alemayehu and Bitew (Reference Gebru, Alemayehu and Bitew2023).
Abbreviation: AWC, available water content.
Chemical properties of compost, carbonized rice husk, and pre-sowing soil collected by layer (0–20, 20–40, and 40–60 cm)
Abbreviations: AP, available phosphorus; CEC, cation exchange capacity; CRH, carbonized rice husk; EC, electrical conductivity of soil in 1:5 soil to water ratio; MC, moisture content; OC, organic carbon; TN, total nitrogen.
The results of the laboratory analysis of bulk density, proportion of mineral particles, and percentage of available water content showed that the soil has a high water-holding capacity (Table 1). The average bulk density of the top 20 cm soil layer was lower than the critical level, where too little root penetration problem could be observed (Hazelton and Murphy, Reference Hazelton and Murphy2016). The tillable soil depth has a significantly higher water-holding capacity than the subsoil two consecutive soil depths. As the soil depth increases from 0 to 60 cm downward, the soil becomes looser than the top (field observation).
The laboratory analysis report of the soil’s chemical properties is shown in Table 2. The soil is strongly acidic with high organic carbon for the top 40 cm soil depths (Hazelton and Murphy, Reference Hazelton and Murphy2016), medium total nitrogen contents (Tadesse, Haque and Aduayi, Reference Tadesse, Haque and Aduayi1991), and low available phosphorous percentage (Hazelton and Murphy, Reference Hazelton and Murphy2016), which decreases from the top to the bottom layers, thus indicating the necessity of applying P from external sources. The CEC for the tillable layer of the soil in the study site is between 25 and 40 meq/100 g soil, which is classified as high and requires small quantities of liming material. However, answering which SAs should be used for this site needs to be addressed in this study based on the agronomic response of tef to different SAs (see the Result and discussion section).
Experimental materials
A tef crop variety, known as Heber-1 (Dz-Cr-419), was used as a testing crop. This variety was released in 2017 by the Adet Agricultural Research Centre. Heber-1 variety was characterized as high-yielding, with very white seeds, but sensitive to lodging (Chanyalew et al., Reference Chanyalew, Ferede, Damte, Fikre, Genet, Kebede, Tolossa, Tadele and Assefa2019).
SAs—compost (a source of organic matter), carbonized rice husk (a source of silicon), and lime (96% CaCO3, a source of calcium)—were used in this experiment. In addition, urea (46% nitrogen) and triple super phosphate (TSP; 46% P2O5) were used as additional sources of N and P nutrients to maintain nutrient balance respectively.
Treatments and design
Factorial combinations of four CRHT—control without CRH, whole rate during sowing, equal splitting during sowing and tillering, and whole rate during tillering—and four different levels of SAs—compost (10 t ha−1), lime (2.5 t ha−1), compost + lime (10 t ha−1 compost + 2.5 ton ha−1 lime), and control (without any application of SA)—were used in the experiment. A total of 16 treatment combinations of CRHT and SAs were used and laid out in a randomized complete block design with four replications for this experiment. The treatments were laid out on a net and gross plot area of 3 m × 2 m (6 m2) and 15 m × 39.5 m (592.5 m2), respectively. The spaces between adjacent plots and blocks were 0.5 and 1 m, respectively.
Experimental layout and crop management
The experiment was conducted in the dry season under irrigation. Experimental plots were plowed three times using an oxen plow tillage method. The first plow and the second plow were done in October, whereas the third plow was done in November 2020. Smoothing and leveling of each experimental plot were done manually on the same date as sowing.
Seeds of tef (Heber-1 variety) were sown uniformly at a rate of 15 kg ha−1 on a plot of 6 m2 area. The practice of sowing was carried out using a row planting method at a space of 0.2 m, providing a total of 10 rows of tef plants. Before sowing, the SAs were broadcast and incorporated randomly into the experimental plot of each independent block. In addition, the recommended rate of nitrogen (40 kg ha−1) and phosphorous (60 kg ha−1) in the form of urea and TSP, respectively, were uniformly applied for all experimental plots as band application to each row.
For better growth of tef plants, urea was applied in split application with one-third at planting and two-thirds at 41 DAP, whereas TSP was supplied only at sowing. Weeding was carried out manually twice at 30 and 50 DAP. Diazinol was sprayed at the start of panicle initiation to control damage from aphids. At the early stage of the crop (until full emergence), light frequent irrigation was applied every 1–2 day intervals using an overhead sprinkler (watering can), and then during the latter stage, irrigation was done in a fixed interval of every 7 days using the border irrigation method. The moisture content was monitored with the help of a soil moisture meter (Delta-T device, Cambridge, UK) to avoid the risk of crop failure due to water stress. Harvesting was done manually by laying a 1 m × 1 m quadrant excluding the border rows.
Agronomic attributes
The growth data of plant height and panicle length (PL) were measured at the maturity stage on 10 randomly selected plants from the net plot area through a meter tape. Plant height was measured from the ground level to the tip of the panicle, whereas the PL was measured from the node, where the first panicle branch emerges to the tip of the panicle. The leaf area index was measured once during the grain-filling stage using a canopy analyzer (LI-COR Biosciences, LAI-2250, PCH-4750, made in the United States). The number of plants per unit area was recorded on 80 DAP by randomly throwing 0.25 m−2 quadrant into the net plot area and converting it to a unit area. The lodging index was estimated just prior to harvest by observing the degree of stem inclination toward the ground on the whole plot level with a scale of 0–5, where 0 represented 0% and 5 represented 100% plant lodging (Tesfahun, Reference Tesfahun2018; Tekle et al., Reference Tekle, Alemayehu and Bitew2024).
Yield and yield component data of grain and aboveground biomass yield were measured after harvest, which was done by placing 1 m×1 m quadrant randomly to the net plot area. Samples were sun-dried for 1 week until a constant dry weight was obtained, and then manually threshed to separate grains from husks and adjust to 12.5% moisture content (Equation (1)). The grain yield was measured by taking the weight of the grains from the net plot area and converting it to kg ha−1. The harvest index (HI) for each treatment was obtained by dividing the economic yield from the biomass yield:
$$ G{Y}_a=G{Y}_m\ast \left(\frac{\left(100- MC\right)}{\left(100-12.5\right)}\right), $$
where GY a is an adjusted grain yield (kg ha−1) at 12.5% moisture content, GY m is the actual grain yield, and MC is the actual moisture content of measured grain yield (%). The Above-ground Biomass Yield (ABY) was measured by weighing the sun-dried plant sample and converted to kg ha−1. The HI was also calculated as the ratio of GY to BY and expressed as a percentage. The water use efficiency of tef was calculated using Equation (2):
$$ WUE=\frac{G{Y}_{\mathrm{a}}}{I_a}, $$
where WUE is the water use efficiency of tef (kg ha−1 m−3) and Ia is the applied irrigation water (m3).
Statistical analyses
Software called R version 4.1.1 was deployed to make the data analysis (Team, 2021). Before making the ANOVA, the normality of the data was checked through the Shapiro–Wilk testing method (Hanusz and Tarasińska, Reference Hanusz and Tarasińska2015; Gebru, Alemayehu and Bitew, Reference Gebru, Alemayehu and Bitew2023). The general linear model’s process was then applied to the ANOVA. Then comparison was performed using the least significant difference approach at the 0.05 probability level when the ANOVA showed significant differences between means of treatment. In the data analysis, the year and replication were handled as random effects, while the water depletion level, silicon application timing, SAs, and CRH rate were treated as fixed variables.
Result and discussion
Plant height, panicle length, and number of plants per unit area
In our experimental result, plant height was only significantly (p < 0.05) affected by the main effects of SAs during 2022 (Table 3). However, the pooled mean analysis result over the 2 years showed no significant difference among all the main, and interaction of treatments. Plant growth parameters, including PL and number of plants per square meter plot area (NP m−2), were not significantly influenced by either the main effects or the interaction of SAs and CRHT in both years. Except for NP m−2, which showed a significant increment, the PH and the PL showed a significant reduction for all the treatments in 2022 than in the 2021 production season. The tef PH had reduced by 23.9% in 2022 compared with 2021. The application of compost in 2022 showed a higher PH, with 5.42% (calculated based on Table 3) compared with the control treatment, which received only the recommended rate of inorganic fertilizer. Despite not being significant, the application of only inorganic fertilizer provided a slightly higher observed PH than all other SAs along with inorganic fertilizers in 2021 than in 2022. The pooled mean analysis result showed that compost application provided significantly (p < 0.05) higher PH than the application of lime. This result was the same for PL of tef (Table 3).
The main effect of soil amendments on selected growth parameters of tef
Note: Means with the same letter(s) in a column for individual factors are not significantly different at P = 0.05. The symbol ‘***’ indicates a very highly significant difference at p = 0.0001. The symbol ‘*’ indicates a significant difference at p = 0.05. The acronym ‘ns’ indicates a nonsignificant difference at p = 0.05. The significance of the bold entries was ***, indicating very highly significant difference (p =0.0001), which is shown by year. Abbreviations: CRHT, carbonized rice husk application timing; CV, coefficient of variation; LSD.05, least significant difference at a probability level of 0.05; NP, number of plants; PH, plant height; PL, panicle length; SA*CRHT, interaction of SA and CRHT; SA, soil amendments; Y*CRHT, interaction of year and CRHT; Y*SA*CRHT, interaction of year, SA, and CRHT; Y*SA, interaction of year and SA.
Optimum plant growth could be used as a good estimator of plant lodging (Zhou et al., Reference Zhou, Gu, Cheng, Yang, Shu and Sun2020) and the final yield (Ngoune Tandzi and Mutengwa, Reference Ngoune Tandzi and Mutengwa2019) of crops particularly tef. Plant height, PL, and number of plant stands per unit area of land are important traits, among others, used in this regard, and observing their change in response to the treatments imposed was found to be relevant. The significant difference in PH during the second year could be due to the quality of SAs, crop management, and weather conditions of the season. This result was in line with the finding of Hunegnaw et al. (Reference Hunegnaw, Alemayehu, Ayalew and Kassaye2021), who stated a decline in PH and PL by 4.4% and 2.9%, respectively, relative to the first growing season due to the application of 10 t ha−1 compost. This could be due to the relatively poor quality of compost that may arise from high moisture content (Guo et al., Reference Guo, Li, Jiang, Schuchardt, Chen, Zhao and Shen2012), which hindered the growth of tef in 2022 than the 2021 production year. The cover crop (Niger seed) planted in the main rainy season of 2021 with the residual nutrient might cause a reduction in soil nutrient depletion dominantly nitrogen that may affect tef production during the second tef production (Wagg et al., Reference Wagg, van Erk, Fava, Comeau, Mitterboeck, Goyer, Li, McKenzie-Gopsill and Mills2021). The increase in NP m−2 and the decrease in PH and PL were in line with the result of Reda, Dechassa and Assefa (Reference Reda, Dechassa and Assefa2018), who found a 75.5% increase in NP m−2 and 9.4% and 1.84% reduction in PH and PL of tef, respectively, with an increase in seed rate from 2.5 to 5 kg ha−1 (Reda, Dechassa and Assefa, Reference Reda, Dechassa and Assefa2018). The higher PH caused by compost than lime could be due to the additional nitrogen supply from compost material. This was in line with the result of Hunegnaw et al. (Reference Hunegnaw, Alemayehu, Ayalew and Kassaye2021), who found 8.2% higher straw yield from compost compared with lime application.
Chlorophyll content of tef
The chlorophyll content of tef was significantly (p < 0.05) influenced by the application timing of carbonized rice husk (Fig. 2). The application of the whole rate of CRH during sowing (CRHT2) recorded the lowest CC (29.7, 33.0, and 19.2 nmol cm−2) at the first to the third growing periods, respectively, compared with other treatments, except the last period showing the highest CC than any other treatments. During the first period of tef growth, CRHT3 provided 8.1% higher CC than CRHT2, but during the late plant growth period, the value was reversed, and CRH3 showed 7.4% lower CC than the CRH2 treatment. All four treatments showed a similar trend over time regarding CC, where the maximum was observed during the development stage (31 DAP), while the minimum was recorded at the crop maturity stage.
Effect of carbonized rice husk timing on the chlorophyll content of tef at different growth periods. Treatments (within the same date group) that are connected with the same letter(s) are not significantly different at p = 0.05. The coefficients of variation for the four chlorophyll measurement periods—16, 31, 46, and 61 days after planting—were 7.4%, 8.6%, 17.1%, and 19.7%, respectively.
The highest CC of tef leaves observed from whole rate application during the sowing over the other treatments could be attributed to the slow release of available silicon over the growing season since the availability and release of silicon depends on the temperature during CRH preparation (Olanrewaju, Sato and Masunaga, Reference Olanrewaju, Sato and Masunaga2024). The decline in CC during the late season stage could be related to nitrogen translocation to grain (Saberioon et al., Reference Saberioon, Amin, Anuar, Gholizadeh, Wayayok and Khairunniza-Bejo2014).
Water use efficiency, lodging, and leaf area indices
The individual year analysis result showed that the application of SA had significantly affected lodging index (p < 0.05) in both production years. On the other hand, SA influenced the leaf area index significantly (p < 0.001) in 2021 and (p < 0.01) in 2022. The combined analysis over the years indicated that lodging index and leaf area index were influenced significantly by the SAs at p < 0.01 and p < 0.001, respectively. The timing of carbonized rice husk application has significantly (p < 0.001) influenced the lodging index of tef in 2021, but not in the 2022 production season (Table 4). The result from the pooled mean analysis of variance showed the significant effect of CRHT (p < 0.001) treatment on lodging of tef. The pooled mean analysis result showed the presence of significant (p < 0.001) variation over the growing season on traits of lodging index and leaf area index (Table 4). However, there was no significant (p > 0.05) interaction effect of SA and CRHT in both the individual and pooled mean analysis of variance results on the water use efficiency of tef.
The effect of soil amendments and carbonized rice husk application timing on water use efficiency, lodging, and leaf area indices of tef crop grown under irrigation
Note: SA1, SA2, SA3, and SA4 are treatments without lime and compost, with compost, with lime, and with their combination, respectively; LSD.05 is the least significant difference at a probability level of 0.05. Means with the same letter(s) in a column for individual factors are not significantly different at P = 0.05. The symbol ‘***’ indicates a very highly significant difference at p = 0.0001. The symbol ‘**’ indicates a highly significant difference at p = 0.01. The symbol ‘*’ indicates a significant difference at p = 0.05. The acronym ‘ns’ indicates a nonsignificant difference at p = 0.05. For lodging index, the variation over years was highly significantly different (p =0.01); for lodging index, the variation over the years was very highly significant difference (p = 0.0001) were mentioned in bold. Abbreviations: CRHT, carbonized rice husk application timing; CV, coefficient of variation; LAI, leaf area index; LI, lodging index; LSD, least significant difference; SA*CRHT, interaction of SA and CRHT; WUE, water use efficiency; Y*CRHT, interaction of year and CRHT; Y*SA*CRHT, interaction of year, SA, and CRHT; Y*SA, interaction of year and SA.
The lodging index has shown an increment with the application of compost and lime that could be attributed to an increase in plant height and PL (Table 4). The lowest lodging index was recorded from the application of lime, with a statistically similar impact obtained from the control treatment. However, treatments that received compost with or without lime showed an increased sensitivity of the plants to lodging (Table 4), which could be attributed to the change in plant height caused by additional nitrogen supply, which is released from compost (Table 3). The result was in line with that of Tefera et al. (Reference Tefera, Belay and Sorrells2001), who stated a highly significant positive correlation between lodging index and plant height. The lodging sensitivity increased from the absolute control treatment (23.4%) that received no carbonized rice husk application to whole rate application during tillering (42.7%). The whole rate application of carbonized rice husk at sowing had the second-best lodging tolerance, but it was indifferent to half CRH applied during sowing and half during tillering. This result was in agreement with that of Gebru, Alemayehu and Bitew (Reference Gebru, Alemayehu and Bitew2023), who stated an increased lodging index with the application of CRH, which could loosen the soil physical structure that results in low anchorage ability of tef crop.
Yield and yield components
Grain, aboveground biomass, and straw yields are key traits of tef crop, which are preferred by the farmers to boost their income (Gelaw and Qureshi, Reference Gelaw and Qureshi2020; Barretto et al., Reference Barretto, Buenavista, Rivera, Wang, Prasad and Siliveru2021). Thus, improving these traits with the application of SAs at a proper growth stage could be essential. Our experimental result showed that the combined application of compost (10 t ha−1) and lime (2.5 t ha−1) had significantly affected grain yield (p < 0.001) and aboveground biomass yield (p < 0.01) in 2022 but not in 2021 (Table 5). In the case of the straw yield trait of tef, there was significant (p < 0.05) influence from SA in both 2021 and (p < 0.01) in the 2022 growing season. The combined analysis results over the two experimental years showed that both the aboveground biomass and straw yields were influenced by the main effect of SA (p < 0.01) (Table 5). The grain yield and HI of tef were significantly influenced by the main effect of CRHT in 2021 at p < 0.05 and p < 0.01 levels of significance, respectively. The HI of tef was not significantly (p > 0.05) influenced by the application of SAs. The interaction of SA and CRHT did not significantly (p > 0.05) affect all the selected yield parameters and HI (Table 5). The tef grain yield showed significant variation over the years with a 72.5% increment from 2022 to 2021.
The effect of soil amendments and carbonized rice husk application timing on the yield and yield components of tef
Note: The symbol ‘*’ indicates a significant difference at p = 0.05. The symbol ‘**’ indicates a significant difference at p = 0.01. The symbol ‘***’ indicates a significant difference at p = 0.001. The dot symbol indicates a significant difference at p = 0.1. The yearly variation was very highly significant difference (p = 0.0001) for both grain yield and above-ground biomass yield were mentioned in bold. The acronym ‘ns’ indicates a nonsignificant difference at p = 0.05. Abbreviations: ABY, aboveground biomass yield; CRHT, carbonized rice husk application timing; CV, coefficient of variation; GY, grain yield; HI, harvest index; LSD, least significance difference; ns, nonsignificant difference; SA*CRHT, interaction of soil amendment and carbonized rice husk application timing; SA, soil amendment; SY, straw yield; Y*SA*CRHT, interaction of year, soil amendment, and carbonized rice husk application timing; Y*SA, interaction of year and soil amendment.
The significant increase in grain yield in 2022 than in 2021 could be attributed to the residual effect of compost, which releases nutrients slowly into the soil (Shaji, Chandran and Mathew, Reference Shaji, Chandran and Mathew2021). However, the result was not in line with that of Hunegnaw et al. (Reference Hunegnaw, Alemayehu, Ayalew and Kassaye2021), who found a decrease in GY during the second growing season than the first year with the application of farm yard manure, which could be attributed to the stability of the form of organic matter that increases the nitrogen content, water-soluble substances, and lignin content (Levi-Minzi, Riffaldi and Saviozzi, Reference Levi-Minzi, Riffaldi and Saviozzi1986). This is also in agreement with Hepperly et al. (Reference Hepperly, Lotter, Ulsh, Seidel and Reider2009), who found the highest soil nutrient level compared to fresh manure and synthetic fertilizers. The nonsignificant difference in the HI of tef could be due to the proportional change observed in the grain and biomass yields and the level of association among the trails (Gebru, Alemayehu and Bitew, Reference Gebru, Alemayehu and Bitew2023).
Conclusion
The result of this study indicated that SAs had significantly influenced the lodging index and leaf area index of tef. The application of compost + lime significantly improved tef grain, aboveground biomass, and straw yields by 12.1%, 14.5%, and 15.2%, compared with lime, and 12.3%, 9.3%, and 8.4%, respectively, compared with the control treatments that received no SAs, respectively. Compost alone and its combination with lime showed a significantly sensitive response to lodging in the range of 13.9%–44.9% compared with lime and control treatments. In addition, except pant height, which was significantly influenced by SAs in the 2022 growing season, both PL and number of plants per square meter were not significantly affected by the main and interaction SAs and CRHT. Moreover, water use efficiency of tef was not significantly improved by SAs, carbonized rice husk timing, or their interaction. For the applicability of the research finding, we recommend that it should be conducted over location and seasons on a fixed plot treatment experimental arrangement as the organic SAs effect is well expressed with residual effect over a longer period than in the short term.
Funding statement
The authors duly acknowledged the Sustainable Enhancement of Irrigated Tef (SENIT) project, funded by the Research and Community Service Office, College of Agriculture and Environmental Sciences, Bahir Dar University. M.G.T. also acknowledged Wolkite University under the Ministry of Education, Federal Democratic Republic of Ethiopia, for their support, including tuition fees and additional research support.
Competing interests
The authors report there are no competing interests to declare.
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