Optimizing Inter-row Spacing and Blended NPS Fertilizer to Boost Production of Sorghum (Sorghum bicolor (L) Moench) and Ensure its Economic Feasibility

Optimizing Inter-row Spacing and Blended NPS Fertilizer to Boost Production of Sorghum (Sorghum bicolor (L) Moench) and Ensure its Economic Feasibility Abas Aden Ahmed1, Walelign Demisie2 1 - Plant Science Department, College of Dryland Agriculture, Kebridaher University, Ethiopia 2 - Department of Plant Science, College of Dryland Agriculture, Jigjiga University, P.O.Box 1020, Jigjiga, Ethiopia Corresponding author: Walelign Demisie, e-mail: [email protected] Received: 20 May 2025 Accepted: 25 July 2025 Abstract Due to varietal variation in architecture, the conventional inter-row spacing of 75 cm is not always applicable to all varieties in sorghum production. Similarly, the blanket fertilizer recommendation assumes equal fertility levels across all soil types, making it unsuitable. Thus, a field experiment was conducted to find the optimum rate of blended NPS and inter-row spacing for sorghum in Southeast Ethiopia. The experiment consisted of a factorial combination of five NPS levels (0, 50, 100, 150 and 200 kg NPS ha-1) and three inter-row spacing (55, 65 and 75cm). The treatments replicated thrice with randomized complete block design. The results showed that NPS fertilizer and inter-row spacing had significant (P<0.05) effect on various parameters, but their interaction effect had no significant effect (P>0.05) on all parameters. Increased inter-row spacing and NPS rate prolonged days to flowering and maturity. The increase in the rate of NPS and interrow spacing significantly increased leaf area, leaf area index, panicle weight, and 1000kernel weight. Similarly, plant height increased with increasing rate of NPS but decreased with increasing inter-row spacing. The maximum grain yield (3336.81 kg ha-1) and biomass weight (7900.01 kg ha-1) were recorded with a rate of 150 kg NPS ha-1, while the lowest grain yield (1730.21 kg ha-1) and biomass (5660.44 kg ha-1) were obtained under nil-treated plots. The highest grain yield (2734.27 kg ha-1) and biomass (7490.12 kg ha-1) were recorded with spacing of 65 cm. The partial budget analysis showed that the highest net benefit of 85,913 birr ha-1 with maximum marginal rate of return (2534.22%) was obtained in the treatment that received 150 kg NPS ha-1 with 65 row-spacing. Therefore, 150 kg ha-1 blended NPS with 65 cm inter-row spacing is recommended in the study area and in dry and semi-arid regions with similar agro-ecological conditions. Key words: blended NPS fertilizer, marginal rate of return, sorghum, spacing, yield Bulgarian Journal of Soil Science® 2025 Volume 10. Issue 2. www.bsss.bg 136 Introduction Sorghum (Sorghum bicolor (L.) is a crucial drought-resistant grain crop that is cultivated in dryland areas of the world (Agrama and Tunstra, 2003; Kumara et al., 2011). It is a staple crop in arid and semi-arid parts of Africa and Asia (Hariprasanna and Rakshit, 2016). Thus, it is the second most important cereal (after maize) in sub-Saharan Africa (Prajapati et al., 2018). In East Africa, sorghum is primarily produced in altitude ranging from 900 to 1,500 m (Terefe, 2017). The crop is grown in Ethiopia’s multiple agroecological zones. However, it is predominantly produced in dry areas that cover nearly 66% of the total area of Ethiopia (Geremew et al., 2004). Because of its drought resistance, sorghum is the crop of choice for dry regions and areas with unreliable rainfall (Terefe, 2017). Grain yield of sorghum differs across the various parts of the world. From 2001 to 2020, the average sorghum grain yield in the world was 2.5 t ha-1 (Khalifa and Eltahir, 2023). However, it was 4.5 t ha-1 in developed countries. In sub-Sahara countries, except for South Africa (which achieved a maximum grain yield of 4.0t ha-1), the yield of sorghum was significantly lower. For instance, in Ethiopia the average sorghum grain yield was 2.0 t ha-1 (Khalifa and Eltahir, 2023). A major problem for the low productivity of sorghum is the decline in soil fertility accompanied by a lack of appropriate agronomic practices like proper plant spacing. In dryland areas, optimizing plant spacing and fertilizer application based on crop architecture and resources (Frantová et al., 2024) is effective strategy for maximizing yields and minimizing the potential for crop failure (Haarhoff and Swanepoel, 2022) due to limited water availability. Adjusting rows spacing and fertilizer management are key measures to avoid competition, reducing soil evaporation (Mupangwa and Wegary, 2018), enhance light interception and increase photosynthesis (Khan et al., 2017), and ensure productivity (Piao et al., 2022). According to Zheng et al. (2019), fertilization, plant density, row spacing, and a variety of other factors all have a favorable effect on grain yield. Row spacing plays an important role in determining plant density under dry land conditions (Mashiqaa et al., 2022). Optimizing planting density improves light capture, air circulation, and resource usage, resulting in uniform growth, decreases nutrient competition, and supports sustainable weed management, leading to higher yields (Tang et al., 2025). Although drought tolerant and early maturing sorghum varieties have been developed and disseminated to the community, the majority of the developed varieties were not widely adopted in the Southeastern Ethiopia since they were not preferred by agro-pastoralists. Most agro-pastoralists preferred landraces and late maturing variety for their biomass apart from the grain yield. These varieties are drought-susceptible, low yield, and long maturity. Thus, due to the recurrent drought and climate effect, the community was convinced to adopt early maturing variety with smaller biomass. In Ethiopia, the recommended spacing for sorghum is 75 cm between rows and 20 cm between plants. The spacing was set based on the morphology of tall and late maturing sorghum varieties. But, the community in the semi-arid area of Southeastern Ethiopia applies this spacing for early maturing sorghum varieties either. Therefore, it is advisable Ahmed & Demisie, 2025 Bulgarian Journal of Soil Science® 2025 Volume 10. Issue 2. www.bsss.bg 137 to determine the right spacing for early and short sorghum varieties which have relatively small canopy. In Ethiopia, for the last few decades nitrogen and phosphorous containing fertilizers (in the form of urea and DAP) had been used for all crops. Such unbalanced application of plant nutrients may aggravate the depletion of other important nutrient elements in soils such as K, S and micronutrients (Zn and B) (EEA, 2005). Application of blended fertilizer (19% N, 38% P2O5 and 7% S) is crucial to increase production and productivity of crops. The Sulfur in blended NPS makes it different from the DAP. Plant tissue requires similar amount of sulfur as that of P (Narayan et al., 2022) because they are building block of protein. Crops cannot produce their maximum amount of protein or yield without adequate sulfur (Zhao et al., 1996). Application of sulfur also decreases soil pH which is very essential in study area where the soil is calcareous. In response to these challenges, blended NPS fertilizer has been recently introduced in market of study area. However, there is little information about the optimum rate of blended NPS in the study area. Therefore, this study was designed to assess the effect of blended NPS fertilizer and inter-row spacing on productivity of sorghum in Southeastern Ethiopia. Materials and Methods Description of the Study Area The study was conducted at Upper Fafen Sub-Basin, Somali Regional State, Ethiopia. Fafen is located 9° 20’ N latitude and 45° 56’ E longitude and has an elevation of 1,650 m above sea level (Degefu et al., 2011). Distance of the sites is 596 km from Addis Ababa to the East and 35 km from Jigjiga town to the west. The area has bi-modal rainfall pattern (from March to early June (Gu’) and the main rainy season from July to late November). With an average yearly rainfall of 400–600 mm, the region is primarily semi-arid and arid (Keskes et al., 2013). According to NMSA (2004), the average annual minimum and maximum temperatures are 16–20 °C and 28–38 °C, respectively. Planting Materials Meko-1 is sorghum variety which is released by Melkassa Agricultural Research Centre in 1998. It is an open pollinated variety (OPV) that can withstand drought. Blended fertilizer NPS (19% N, 38% P2O5 and 7% S), and urea (46% N) was used as source of fertilizer. Two separate applications of urea were made at the sowing and kneeheight growth stages. Treatment and Experimental Design Five rates of blended NPS (0, 50, 100, 150, and 200 kg NPS ha-1) (supplemented with 100 kg urea) and three inter-row spacings (55, 65, and 75 cm) comprised the treatments. A randomized complete block design with three replications was used to conduct the experiment. Thus, there were 5x 3 = 15 treatment combinations constituting 15 x 3 = 45 plots or experimental units. The size of each plot in the experiment was 15m2 (4m x 3.75 m), 13 m2 (4 m x 3.25 m) and 13.2 m2 (4 m x 3.3 m) for 75 cm, 65 cm and 55 cm inter-row spacing, respectively. All the required data were collected from the middle rows leaving the outer most rows in both sides and some distance at both ends to avoid edge effects. The net harvestable area was 2.25m x 3.6m, 1.9m x 3.6 m, and 1.65 m x 3.6 m for 75 cm, 65 cm and 55 cm row spaced plots, respectively. Each experimental plot Ahmed & Demisie, 2025 Bulgarian Journal of Soil Science® 2025 Volume 10. Issue 2. www.bsss.bg 138 and blocks were separated by 1 m and 1.5 m spacing, respectively. The recommended intra-spacing of 20cm between plant was used. Table 1. Nutrient composition of blended NPS fertilizer and urea in each treatment S/ N Fertilizer rate at planting (kg NPS ha-1) N, P and S applied at planting (kg N, P2O5, S ha-1) 100 kg urea (kgN ha-1) Total N, P and S (kg N, P2O5, S ha-1) 1 0 0 0 0 kg N, 0 kg P2O5, 0 kg S 2 50 kg NPS 9.5 kg N, 19kg P, 3.5 kg S 46kg N 55.5 kg N,19 kg P2O5,3.5 kg S 3 100 kg NPS 19 kg N, 38 kg P,7 kg S 46kg N 65 kg N, 38 kg P2O5, 7 kg S 4 150 kg NPS 28.5 kg N,57 kg P,10.5kg S 46kg N 74.5 kgN,57kg P2O5,10.5 kg S 5 200kg NPS 38kg N, 76 kg P, 14kgS 46kg N 84 kg N, 76kg P2O5, 14kgS Experimental Procedures Before planting, the land was prepared thoroughly, cleaned, leveled and made suitable and available for planting. While conducting the experiment, all the recommended agronomic practice was kept constant except the different levels of interrow spacing and NPS rates used as treatment in the study. Sorghum seeds (Meko-1 variety) were planted at rate of two seeds per hill then, after emergence it was thinned to one seedling per hill. At time of planting, all plots received a basal application of different rate of blended fertilizer (NPS) (19% N, 38% P2O5 and 7% S) and 50% of the recommended value of N in the form of urea. Urea was applied at time of planting and the remaining 50%of the urea used as a side dressing at knee height stage. The N was placed about 5 cm away from the plant base during knee height. Supplementary irrigation was applied based on the soil moisture. Plants in the two outer rows were not considered for data collection. Data Collection Days to 50% flowering was recorded as the number of days from the date of planting to the date at which 50% of the plants in a plot flower. Days to Maturity was taken as the time from the date of planting until the grains from the main shoot reached to the black layer stage. Plant height, leaf area and leaf area index data were taking from five representative sample plants at 50% flowering. Plant height (cm) was measured from the ground level to the base of the panicle. The leaf length and width of representative plants’ sample were taken and then the leaf area (cm2) was determined by using the method developed by Sticker et al. (1961) as: 𝐿𝐴=𝐿∗𝑊∗0.75 where, LA: Leaf Area, L: Leaf Length, W: Maximum Width of the leaf, 0.75: correction factor for sorghum. The leaf area index (LAI) was calculated as the ratio of the leaf area to the area of land occupied by the plant. Number of productive tillers was determined as the number of productive tillers counted for ten sampled plants from each net plot area. Five plants were selected from each plot, and the length of the panicle (cm) was measured from the base to the tip at maturity. Panicle weight (g) was determined by weighing of all harvested panicles from Ahmed & Demisie, 2025 Bulgarian Journal of Soil Science® 2025 Volume 10. Issue 2. www.bsss.bg 139 each net plot. Thousands kernel weight (g) was determined by counting 1000 kernel and adjusting to 12.5% moisture level before weighing them using sensitive balance. Above ground dry biomass weight was determined by weighing the sun dried plants taken from the net plot at harvesting time. The grain yield was determined by weighing the grains collected from net plot, then adjusting to 12.5% moisture level, and converting them to per hectare bases. Harvest index (HI) was determined by taking the ratio of grain yield to the total biomass yield HI= X100 Soil Analysis Before planting, a composite soil sample at a depth of 0-20cm, representing each plot was taken for determining the physiochemical parameters of the soil of the experimental site. Economic analysis The economic analysis was performed based on CIMMYT (1988) in which the local market prices for inputs at planting and for outputs at harvesting were used. In this analysis, all the costs and benefits were computed on hectare basis in Ethiopian Birr. The concepts used in the partial budget analysis were the mean grain yield, the gross benefit (GB) ha-1 (the mean yield for each treatment) and the field price of fertilizers. Marginal rate of return refers to net income obtained by incurring a unit cost of fertilizer and its application. Unadjusted grain yield (UGY) (kg ha-1) refers to an average yield of each treatment. Adjusted grain yield (AGY) (kg ha-1) refers to the average yield adjusted down ward by a 10% to show the difference between the experimental yield and yield of farmers. Adjusted yield multiplied by farm price was used to determine gross field benefit (GFB) (ETB ha-1). GFB = AGY × farm price for the crop. Total variable cost (TVC) ETB ha-1) was calculated by summing up the costs that vary, including the cost of NPS fertilizer, urea and the average open price of sorghum at Jigjiga market and labor cost. To calculate the net benefit (NB) the difference between the gross benefit (GFB) and the total cost that vary (TCV) was taken. i.e. NB= GFB– TCV. Each pair of ranked treatments, % marginal rate of return (MRR) was calculated using the formula: ( ) ( ) Where, NB a=immediate lower, NB b=next higher, TVC a=immediate lower TCV, TCV b=next higher TCV, the treatment with highest net benefit and Higher MRR was considered for recommendation. Statistical Data Analysis Using SAS software, the acquired data was put through an analysis of variance (ANOVA) appropriate for the design. The mean separation was performed using LSD at 0.05 level of probability. Pearson correlations were done to determine linear associations between selected agronomic parameters. Ahmed & Demisie, 2025 Bulgarian Journal of Soil Science® 2025 Volume 10. Issue 2. www.bsss.bg 140 Results and Discussion Weather and Physio-Chemical Properties of the Experimental Site The experiment was conducted during the main cropping season under rain-fed condition. The annual of rainfall for the crop growth duration was 240.9 mm and the annual rainfall was 441.3 mm. But the crop requires an average annual precipitation of 455-800 mm (Balasubramaniyan and Palaniappan, 2004). It shows that the pattern of rainfall of research area during the growing period was below the water requirement of the crop. Thus, this rain-fed experiment was supplemented with irrigation. During the crop growth period the mean temperature was 21.350c with the mean minimum and maximum temperature of 14.250c and 28.10c, respectively. The soil analytical results indicated that the soil pH is 7.8 showing mildly alkaline nature of soil (Hazalton and murphy, 2007). The soil pH falls in the optimum range of pH requirement sorghum (Espinazo and Kelley, 2005), implies soil pH of the experimental site was suitable for sorghum production. The result of the soil analysis also shows that the soil of the research area can be classified as sandy clay loam that contain total N of 0.10% which falls in the low range (0.05-0.15), 6 ppm available phosphorus also falls in the low range (5-10 ppm) and 1.50% organic carbon which is in the low range (1.01.71%) (Hazelton and Murphy, 2007). It indicates that the soil in the study area is low in total N, available P, and organic carbon. Therefore, application of fertilizer rich in N, P and organic C is recommended. Crop phenology and Growth of Sorghum The result indicated that days to flowering and days to physiological maturity were significantly (P < 0.01) influenced by NPS fertilizer and inter-row spacing (Table 2). Days to 50% flowering was significantly affected by NPS with the longest day to flowering (74.67days) was recorded for the plots received the highest rate (200 kg NPS ha-1), while the earlier flowering (65days) was registered under nil-treated plots (Table 2). Amjad et al. (2005) also reported the days to flowering increased with the increase rate of fertilizer .This is attributed to the nitrogen fertilizer that enhanced vegetative growth and thus delayed flowering (Bilekudari et al., 2005). Likewise, days to flowering was significantly affected by inter-row spacing with the prolonged days to flowering (70 days) was observed with inter-row spacing of 75cm (Table 2). This is because widely spaced plants may have experienced luxurious vegetative growth due to ample growth resources which resulted in delayed flowering. As the rate of NPS increased the days to physiological maturity delayed. The longest days to maturity (116.3 days) was recorded for the plants treated with 200kg NPS ha-1, while the earlier maturity (103.4 days) was recorded for nil-treated plots (Table 2). The higher application of nitrogen could enhance vegetative growth and thus increased days to maturity (Dawadi and Sah, 2012; Hussein and Leitch, 2007). This would have a negative impact on study area where moisture deficit is a serious issue. Thus, optimizing the rate of fertilizer is essential to cope with such challenges. Similarly, increasing inter-row spacing increased the days to maturity (Table 2). The longest days to maturity (113 days) was recorded at 75 cm inter-row spacing while the earliest days to maturity (107 days) was recorded at 55cm inter-row spacing (Table 2). Ahmed & Demisie, 2025 Bulgarian Journal of Soil Science® 2025 Volume 10. Issue 2. www.bsss.bg 141 Negash et al. (2017) also found that compared to plants produced at broader row spacing, sorghum plants planted at 55 cm row spacing had noticeably shorter days to maturity. The early physiological maturity due to narrow-row spacing might be due to the intense interspace competition which led to the depletion of the available nutrients and as result plants tended to mature earlier. The results showed a significant influence of NPS and inter-row spacing on growth parameters such as on plant height and leaf are per plant. Plant height increased progressively with the increase in rate of NPS, from values of 156.02 to 170.08 cm with NPS increasing from 0 to 200 kg ha-1. This could be the contribution of nitrogen and sulfur promotes the formation of chlorophyll for photosynthetic activity (Rao et al., 2001) and phosphorous enhances the shoot and root development which in turn resulted in vigorous vegetative growth. The tested inter-row spacing predominantly influenced the height of plants, where increasing inter-row spacing decreased plant height. The tallest plant (164.20cm) was measured from 55 cm inter-row spacing and the shortest plant (161.82cm) was recorded with the conventional spacing of 75cm (Table 2). Plants in the higher planting density become taller as a result of competition of plant for light ( Miko and Manga, 2008). As the rate of NPS rose, the leaf area grew as well. The maximum leaf area (1988 cm2) was measured for plants received 200 kg NPS ha-1 which is in parity with rate of 150kg NPS ha-1. Whereas, the lowest leaf area (1543.01 cm2) was recorded from niltreated plots. This result is in conformity with the work of Chimdessa (2016) and Berhane et al. (2015) who reported that application of fertilizer increased the leaf area. This could be the increased NPS resulted in vigorous growth of the crop and leaf expansion in length and width. Leaf area increased with the increase in inter-row spacing, from value of 1689.66 to 1706.19 and 1963.40cm with spacing increasing from 55 to 65 and 75cm, respectively. The lowest leaf area for the crop grown with the narrower spacing could be due to interplant competition for light and mineral nutrients among highly populated plants. As the rate of NPS increased, the leaf area index rose as well. The highest Leaf area index (1.44) was recorded for 200 kg NPS ha-1 treated plots, while the lowest (1.13) was recorded for nil-treated plots. Our findings were supported by Addai and Alimiyawo (2015) who reported that the application of NP fertilizers to the sorghum significantly increased leaf area and LAI. The increase of LAI could be attributed to more production of expanded leaves in response to nitrogen. Ahmed & Demisie, 2025 Bulgarian Journal of Soil Science® 2025 Volume 10. Issue 2. www.bsss.bg 142 Table 2. Effect of NPS and inter-row spacing on crop phenology and growth of sorghum Treatment Days to flowering Days to maturity Plant height (cm) Leaf area per plant (cm2) Leaf area index NPS rate ( kg ha-1) 0 65.78d 103.40c 156.02d 1543.01c 1.13c 50 67.22c 106.84bc 159.54c 1697.45bc 1.15c 100 69.33bc 107.81b 162.21b 1813.17ab 1.21bc 150 70.67a 114.34a 169.70a 1938.11a 1.32ab 200 74.67a 116.33a 170.08a 1988.00a 1.44 a P value ** ** ** ** * LSD(0.05) 1.094 1.968 1.120 187.6 0.1523 Inter-row (cm) 55 67.87b 107.41b 164.20a. 1689.66b 1.20a 65 67.87b 108.82b 163.83b 1706.19b 1.34a 75 70.80a 113.01a 161.82c 1963.40a 1.22a P value ** ** ** ** NS LSD(0.05) 0.848 1.968 0.868 145.3 NS CV 1.6 2.4 0.7 10.9 12.6 LSD = least significant difference; CV= coefficient of variation (%). Means in the same column followed by the same letter(s) are not statistically significantly different at a 5% probability level. Yield and Yield Components of Sorghum The findings demonstrated that inter-row spacing and blended NPS had a substantial impact on sorghum production and yield components (Table 3).The tiller number increased significantly (P<0.01) with the increased in NPS rates. The maximum number of tiller (13.09) was recorded under application of 200 kg NPS ha-1; while the lowest number of tiller (8.31) was recorded for the nil-treated plots. The added N and P might have played a vital role in cell division. The tested inter-row spacing predominately influenced the tiller number of plants, where the significantly highest tiller number (12.1) were found in the row spacing of 75cm while the lowest tiller number (8.88) in the row spacing of 55 cm. Higher number of tillers for wider row-spacing, most likely related to Ahmed & Demisie, 2025 Bulgarian Journal of Soil Science® 2025 Volume 10. Issue 2. www.bsss.bg 143 better access to space, nutrients, water, and light in wider spacing. Mosavi (2009) also reported that decrease in number of tillers with increasing plant population per unit area. When the rate of NPS was increased from 0 to 150 kg NPS ha-1, the panicle length increased significantly. However, this parameter reduced when the rate of NPS was increased above 150 kg NPS ha-1. Application of 150 kg NPS ha-1 had resulted in about 26.28% higher panicle length over control treatment (Table 3). Our results supported by findings of Weldegebriel et al. (2018) and Gebrekorkos et al. (2017) who reported that increase NPS fertilizer increased panicle length. Similarly, increasing inter-row spacing significantly (P<0.01) increased panicle length. The maximum panicle length (23.51cm) was measured for the widest inter-row spacing (75 cm), while the minimum (21.53 cm) was measured for the narrowest (55 cm) spacing. The widely spaced plants have higher number of panicle length because they are more effective in mobilizing photosynthetic for panicle length and grain filling compared to closely spaced plants (Hasanuzzaman et al., 2009). Apart from panicle length, the panicle weight is one of yield components that determine the grain yield of sorghum. In response to increasing the rate of NPS, the panicle weight increased significantly. It shows that the impact of the essential nutrients in enhancing the seed holding capacity of the panicle. It was also observed that the panicle weight increased with the increase in inter-row spacing. Rajput et al. (1983) also reported that heavier panicle was obtained from widely spaced (less populated) plants than the densely populated plants. The higher panicle weight due to wider row spacing was probably caused by greater availability of growth resources with less inter competition. The thousands kernel weight is very important measure of seed quality, indicating application of the optimum amount of fertilizer and keeping the right plant row-spacing is crucial for better seed quality. Thousand kernel weights were significantly (P<0.01) affected by NPS with the highest values registered for the plants grown under highest rates (200 kg ha-1); however there were no statistical significant differences in this parameter due to the three higher NPS rates (100, 150 and 200kg ha-1). Chimdessa (2016) also reported a significant difference on thousand-kernel weight of maize due to the effect of blended fertilizer. The more kernel weight could be due to contribution of the nutrients in photosynthesis process and translocation of the assimilates to storage organs (seeds). Similarly, thousand kernel weights were significantly (P<0.01) affected by inter-row spacing with the highest values were obtained (39.92g) with a row spacing of 75cm, while decreases of 5.83% and 7.01 % were observed with spacings of 65 and 55cm, respectively. The higher thousands kernel weight noted in wider-rows might be due to a more efficient utilization of water, nutrients, and light due to minimal inter-row competition and lower plant population. The result showed that grain yield of sorghum was highly significantly (P≤0.001) influenced by the main effect of blended NPS fertilizer and inter-row spacing. The maximum grain yield (3336.81 kg ha-1) was recorded under rate of 150 kg NPS ha-1 which was statistically in parity with 200kg NPS ha-1, while the lowest grain yield (1730.21 kg ha-1) was obtained for the control (Table 3), representing an increase of 98.82% compared to the nil-treated plots. 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Benefit-SBN Sesame Business Network Ethiopia. https://www.wur.nl/en/show/2017-sorghum-training-manual.htm Weldegebriel, R. (2020) Effect of blended fertilizer application on yield, nutrient and protein content of sorghum (sorghum bicolor (l.) moench) varieties under rain-fed condition in north western Tigray, Ethiopia. International Journal of Life Sciences, 8(1), 51-58. Ahmed & Demisie, 2025 Bulgarian Journal of Soil Science® 2025 Volume 10. Issue 2. www.bsss.bg 151 Zhao, F. J., Hawkesford, M. T., Warrilow, A. G. S., McGrath, S. P., Clarkson, D. T. (1996). Responses of two wheat varieties to sulphur addition and diagnosis of Sulphur deficiency. Plant and Soil, 181, 317 – 327. Zheng, H.F., Ying, H., Yin, Y.L., Wang, Y.C., He, G., Bian, Q.Q., Cui, Z.L., Yang, Q.H. (2019). Irrigation leads to greater maize yield at higher water productivity and lower environmental costs: A global meta-analysis. Agriculture, Ecosystems & Environment, 273, 62–69. 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