Response of Bread Wheat (Triticum aestivum L.) to Sulfur Fertilizer Rate Under Balanced Fertilization at Basona Warena District of North Shewa Zone of Amhara Region, Ethiopia

Background: Sulphur is becoming an important limiting nutrient to agricultural production in Ethiopian soil. Bread wheat is one of the most important cereal crops produced and consumed in Ethiopia. Declining soil fertility is one of the major factors that accounts for low productivity of wheat in Ethiopia which is caused by soil erosion, continuous cropping of same land year after, deforestation, depletion of organic matter is the main challenge not only to wheat production Methods: The eld experiment was conducted for consecutive three years (2013/14-2015/16) to evaluate effects of S levels on yield and yield components of bread wheat grown on two soil types (Cambisols and Vertisols), North Central of Ethiopia. An experiment consisting of six levels S (0, 10, 20,30,40 and 50 kg ha -1 ) laid out in RCB design with three replications. Results: Results revealed that, yield components were not affected by different levels of S while, yield of wheat were signicantly affected by S in both soil types. S applied on cambisols at 30 and 40 kg ha -1 increased grain yield (GY) of wheat by 9.0 and 10.1 % over control respectively. The corresponding increases on Vertisols were 8.0 and 10.0 % over control respectively. Application of 10 and 30 kg S ha -1 produced the highest MMR (4913.31 and 1277.24%) respectively. Conclusions: The current nding presents additional evidence to research claims that S is becoming a limiting nutrient in some Ethiopian soils. Application of 10 and 30 kg S ha -1 are found to be the most economically feasible treatments for bread wheat production in Cambisols and Vertisols of the district respectively.


Background
Bread wheat (Triticum aesativum L.) is one of the most important cereal crops produced and consumed in Ethiopia. It stands third among cereals in terms of area cultivated annually and grain production next to barley and tef (CSA, 2016). Traditionally, wheat grains are used to prepare household bread, beverage and pancake. It is also processed in factories to produce our for commercial production of bread for consumers in cities and towns. Despite its importance and growing demand for bread wheat in Ethiopia, its production and productivity are desperately very low. The current average productivity of wheat is below 3 t ha − 1 (CSA, 2016) despite its potential productivity greater than 5tha − 1 (Birhan et al., 2016). Consequently, the country imports large amounts (30-50% of total annual demand) wheat grains every year from abroad to meet domestic demand (Minot et al., 2015) which has grave consequence on foreign currency reserve of the country.
Declining soil fertility is one of the major factors that accounts for low productivity of wheat in Ethiopia (Yesuf and Duga, 2000; Amsal et al., 1997) which is caused by soil erosion, continuous cropping of same land year after, deforestation, depletion of organic matter is the main challenge not only to wheat production but also to the production of all crops (Birhan et al., 2016). It is an issue of great concern in Ethiopia as soil nutrient depletion is becoming severe and severe with time since little efforts are being made to reverse the problem.
There were several occasions whereby the yields of crops produced per unit area were increased by more than 100% in many areas of Ethiopia (Kelsa et al., 1992). For example, Gebreyes (2008) reported that application of 92 kg N ha − 1 increased grain yield of wheat by 185% over the control in central Ethiopia.
Thus, due to dramatic positive impact, there was a steady increase in annual fertilizer consumption from 14000 mt in 1974/75 to 500, 000 mt in 2010 (IFPRI, 2012). However, crop yield gain due to N and P fertilizer application is declining over time despite steady increases in fertilizer consumption in Ethiopia (IFPRI, 2010). Declining crop yield responses to N and P fertilizers is attributed to decreasing soil organic matter (SOM) content (IFPRI, 2010). Moreover, depletion of other nutrients in addition to N and P could be additional factor for decreasing response of crops to N and P fertilizers (Wassie and Tekalign, 2013).
Sulphur (S) could be one of the most likely limiting nutrients in Ethiopia soils. Sulphur is one the plant essential nutrients required for their growth and developments and a building block of protein, key ingredient in the formation of chlorophyll (Duke and Reisenaue, 1986). It plays important role in protein synthesis as it is the component of two essential amino acids called cysteine and methionine. It is also a key component of many enzymes in plants. For instances, the S is important component of nitrogenase enzyme, an enzyme that xes atmospheric nitrogen in legume-rhizobia biological nitrogen xation system. Sulphur also interacts with nutrients in soils and the interaction could be positive or negative depending on several factors. For example, Aulakh and Chhibba (1992) observed enhanced root uptakes of P and S when both nutrients were supplied at low rates. Increased uptake and assimilation of N by crops has reported by with adequate than low supply of S (Kumar et al., 2012). Thus, de ciency of S in soils will have adverse consequences on protein synthesis, biological nitrogen xation, chlorophyll synthesis, enzyme activity etc. ultimately compromising yield and quality of crops. It has been reported that S de cient plants exhibits reduced plant height and stunted growth, reduced tillers, spikelets and delayed maturity. Sulfur de cient plants are shown to be less resistance under stress conditions (Doberman and Fairhurst, 2000).
In this regards, emerging research evidences are showing that S one of the nutrients becoming de cient in some Ethiopian soils limiting crop production. For instance, Assefa (2016) studied the response of wheat to S application on 18 sites reported that wheat signi cantly responded to S fertilizer application in 72% of experimental sites. He further reported that soils of responding sites had S content below critical level (11-13 mg kg − 1 SO 4 − 2 -S) for optimum production of wheat.
However, the current assertion that S is becoming nutrient in some Ethiopia soils is based on results of only few experiments and thus it can't be conclusive and de nitive that Ethiopian soils are de cient in S.
Thus, further research is needed to be done to verify the existing claims that S limiting in Ethiopian soils in different soil types. In this regard, there is little or no information so far on the response of wheat to S application in Basona worena district of north Shewa, Ethiopia. Thus, experiment was conducted to determine effects of S application under balanced fertilization on the growth, yield components and yield of wheat and to determine economic feasibility of S fertilizer application of wheat grown on famers' at Basona werna District under two soil types of Vertisols and Cambisols.

Materials And Methods
Description of the study areas

Soil sampling and analyses
After selecting the experimental sites, pre-planting soil samples were collected from each site for the analyses of selected physicochemical properties. Composite soil samples were taken from each site from a depth of 0-20 cm using augur randomly from 15 spots by walking in a zigzag pattern. After thoroughly mixing the composite samples, 1 kg of sub-sample was taken and brought to Debre Birhan agricultural research Centre soil laboratory where it was air dried and grounded to pass 2 mm mesh sized sieve.
The processed samples were analysed for texture following by Bouyoucous hydrometer method (Bouyoucous, 1962). The pH of the soil was measured using pH-water method by making soil to water suspension of 1: 2.5 ratio and was measured using a pH meter. The soil OC content was determined by wet digestion method (Walkley and Black, 1934). Total nitrogen (TN) was determined by using the modi ed micro Kjeldhal method (Cottenie, 1980), available P (ava. P) was analysed by using Olsen's calorimetric method as described by Olsen et al. (1954).

Treatments, design and experimental procedure
The experiment consisting of six levels of S (0, 10, 20, 30, 40 and 50 kg ha -1 ) accompanied by 69P 2 0 5 ,80k 2 0, 92N and micronutrients (2Zn, 2Cu and 0.5B kg ha -1 ) and was laid out in RCB design with three replications. Calcium sulphate (CaSO 4 ), Borax, Zinc Sulphate and Triple super phosphate (TSP) were used as S, B, Zn and P sources respectively. The test crop, wheat variety, Diglo was planted in a unit plot size of 3.6 × 3.4 m with row spacing of 20 cm apart at a rate of 131.25 kg ha -1 . The whole doses of CaSO 4, KCl and TSP fertilizers were applied as basal in both sides of rows just before planting as per the treatment. The Urea-N was split in which one half of N was applied at planting and the remaining one half was applied one month after planting and after weeding. Micronutrients (Zn, B, and Cu) in the form of ZnS04, Borax and CuS04 respectively was applied foliar mode two times at tillers developments stage of the crops. All agronomic management of the trails were done as per the speci c recommendation for the crop.

Data analysis
The collected data were subjected to statistical analysis of variance (ANOVA) and carried out using SAS software program using SAS version 9.

Economic analyses
Partial budget analysis was done to determine economic feasibility of S fertilizer for bread wheat production around the study areas following procedures described in CIMMYT (1998). The mean grain and straw yield data of wheat were employed in the analyses. Furthermore, the grain and straw yield obtained from each treatment were adjusted down by 10% in order to narrow the possible yield gap that may happen due to difference in eld management. The average prices of relevant inputs required to do the partial budget analyses were collected from different sources. The average prices of relevant inputs required to do the partial budget analyses were collected from different sources. Accordingly, the prices of gypsum fertilizer during planting of this experiment was collected from Debire Birhan town. Accordingly, price of gypsum was 1.2 Ethiopian birr (ETB) kg − 1 . The eld prices of grain and straw yield at the district local market around the study area was used. Accordingly, prices of grain and straw yield of wheat were 10.5 and 2.4 ETB kg − 1 respectively.

Soil physical and Chemical properties
Pre-planting soil analyses data of selected physicochemical properties of samples collected from experimental locations at Goshebado (Vertisols) and Gudoberet (Cambisols) are summarized in Table 1. The soils of Goshebado and Gudoberet was belonging to clay textural class. Goshebado soil has soil reaction is ranged from moderately acidic to neutral whereas the soil of Gudoberet is ranged from slightly acidic to neutral reaction (Murphy, 1968). The OC and TN content of both soil types are in low categories according to Tekalign (1991). The available P content of Gudoberet (Cambisols) is medium range while at Goshebado (Vertisols) is ranged from very low to low categories (Olsen et al., 1954). The available soil P value for crop production and yet it is far lower than the critical soil available P value established for some Ethiopian soils which is 8 mg kg − 1 (Tekalign and Haque, 1991).

Effect on growth and yield components of Wheat
On both soil types, growth and yield components of bread wheat didn't respond signi cantly (Table 2). Table 3 showed that effects of S on mean growth and yield components of wheat at both Soils types

Effect on yield of Wheat
Both grain yield (GY) and straw yield (GY) of wheat were signi cantly affected by effects of S application in both Cambisols and Vertisols (Table 2). Data in Fig. 2 showed that effects of S on mean Grain and Straw yield of wheat at both Soils types. On Cambisols, increase in S rate up to 30 kg S ha − 1 ) had a positive effect on grain and Straw yield of wheat while above 30 kg S ha − 1 , yield decreased numerically, but not signi cantly. Application of 20 and 30 kg ha − 1 S have signi cantly increased grain yield by 9.0 and 10.1% over the control respectively and Straw yield by 10.4 and 105% over control respectively. Similarly, on Vertisols, 30 and 40 rates have signi cantly increased grain yield by 8.0 and 10.0% over control respectively and same treatments increased Straw yield by 10.6 and 9.0% over control respectively. Generally, application of S on both soils types improve grain and straw yield of bread wheat. These results are in agreement with the nding of Assefa Menna (2016) who studied the response of wheat to S application and reported that wheat signi cantly responded to S fertilizer application. In another study, Khan et al. 2015) reported that S applied at 20 kg ha − 1 at stem elongation stage signi cantly increased yield of wheat by 28.5% over untreated control. According to DeRuiter and Martin 2001), wheat yield can be increased up to 42% due to S fertilizer depending the inherent S level in particular soils.

Effects of Soil and Years
Results of analyses of wheat response data to over all of the two soils and years are summarized in Table 4. Soils and years have signi cantly affected PH, SPL, NT, BY, GY and STY of wheat. Accordingly, signi cantly higher values of these parameters were obtained in Cambisols than Vertisols. Cambisols, GY and STY were higher by 34.9 and 28.3% over that produced than Vertisols irrespective of treatments. This could be possible be due to better nutrient availability to crop in Cambisols than Vertisols.

Economic Analyses
The results of partial budget analyses data of S fertilizers across two soils are summarized in Table 5. Accordingly, all treatments produced higher and positive net bene t (NB) relative to the control treatment in both soil types, indicating that feasibility of S fertilizer application for wheat production in the study area. In general, NB from application of S fertilizer produced from Cambisols was higher than Vertisols. Consequently, the highest NB (42884.9 and 27074.7 ETB) was produced by application of S at 30 and 40 kg ha − 1 on Cambisols and Vertisols respectively. When it comes to MRR, the highest value of MRR (4913.31 and 1277.24%) was produced by S at a rate of 10 and 30 kg ha − 1 from Cambisols and Vertisols respectively.

Conclusion And Recommendation
The results of this experiment revealed that application of S fertilizer has signi cantly increased yield of bread wheat grown in Cambisols and Vertisols of the study district, northern Shewa, Ethiopia compared to that obtained from unfertilized control. Moreover, the current nding presents additional evidence to research claims that S is becoming a limiting nutrient in some Ethiopian soils which being reported.
Maximum yield of wheat was obtained with treatment involving application of 30 kg S ha -1 and 40 kg S ha -1 from Cambisols and Vertisols respectively. While, partial budget analysis result revealed that, 10 and 30 kg S ha -1 produced the highest MMR (4913.31 and 1277.24%) and thus, those treatments are found to be economically feasible treatments for bread wheat production in Cambisols and Vertisols of the district of Basona worena respectively. Monthly rain fall and average maximum and minimum temperatures in the three years of the study district