Introduction

Low levels of soil fertility because of land degradation and nutrient depletion has been a critical challenge to agricultural production in Ethiopia. On cultivated land, there is a persistent decrease in soil quality coming about because of diminished fallows and imperfect utilization of inputs. Continuous cultivation coupled with nutrient depletion, poor crop residue management, and reduced crop rotation resulted in poor soil fertility1. Most soils in the semi-arid areas of northeastern Ethiopia are intensively depleted of the plant nutrients especially total nitrogen, available phosphorus and organic carbon are characterized by low category for this reason they leading to substantial decline in crop productivity2.

Sorghum is one of the important food crops in Ethiopia that comprises 17% of the total cereal production in the country. It accounts for more than 655671.97 ha total cultivated area in Amhara Region3. But, the average yield of sorghum per unit area is not more than 1.2 t ha−13. Low, erratic, unevenly distributed rainfall and poor soil fertility are some of the causes of low crop productivity including sorghum in Ethiopia4.

Inorganic fertilizer is critically important to increase crop yield5,6. Suggested that fertilizer rates must be expanded to fulfill the regularly expanding need for nourishment. Micro-dosing refers to the application of small quantities of fertilizer at planting or as top dressing about three to four weeks after emergence. Micro-dosing fertilizer increases fertilizer use efficiency and improves yields, while minimizing input and investment cost. This is an effective method to apply fertilizer, because the fertilizer is applied 5 cm adjacent to the seeds, thereby ensuring a high rate of uptake. Micro-dosing of fertilizers was found to increase yields by 44% to 120% and farmers’ income by 52% to 134% compared to traditional application methods (basal application and top dressing)7. Similar research findings in Niger show that micro-dose method increased yield with low cost and efficient8. Likewise9, showed that farmers could boost their yields by 50% by applying about 9 kg of nitrogen per hectare compared to no application in Zimbabwe. In addition, rational use of fertilizer plays its own role to mitigate climate change10. Similarly, micro-dosing fertilizer application could increase the fertilizer use efficiency for the fertilizer is applied to the root zone of the plant and can easily be taken by the plant roots. However, there is no information on fertilizer application in micro-dosing in the study area. Therefore, this research was designed to evaluate micro-dosing fertilizer application techniques (N and P) on sorghum yields at moisture stressed areas of Sekota and Lasta Laibela districts of Amhara region.

Materials and method

Description of the study areas

The study was conducted for two years in 2014 and 2015 at Aybra-Sekota Shimshiha-Lasta Lalibela areas of Amhara Region, Ethiopia respectively (Fig. 1). The location of the study area was found within an altitude ranging from 1921 to1947 m.a.s.l. The study areas are characterized by small (450 mm to700 mm) with erratic rainfall.

Figure 1
figure 1

Location map of study area.

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Experimental design

The experiment was comprised of three NP rates (i.e. 1) 25% of the recommended NP 10.25 kg N ha−1 + 11.5 kg P2O5 ha−1, 2) 50% of the recommended NP = 20.5 kg N ha−1 + 23 kg P2O5 ha−1 and 3) 75% of the recommended NP = 30.75 kg N ha−1 + 34.5 kg P2O5 ha−1) factorially combined with three nitrogen application times (i.e. 1. Two splits: half at sowing and half at emergence, 2. Three splits: one third at sowing, One third at emergence and one third at 45 days after emergence, 3. Two splits: Half at sowing and half at 45 days after emergence) arranged in a completely randomized block design (RCBD) with three replications. In addition, control (without any nutrient) and recommended NP (100 kg ha−1 DAP and 50 kg ha−1 urea) were included to the treatments and made a total of 11 treatments. The recommended NP was applied to the planting rows by drilling (all P once at planting with half of N and the other half of N 45 days after planting). Immediately at planting. Whereas the other fertilizer treatments were applied in a micro-dosing to the spots where the seeds were planted (to the root zone 5 cm soil depth) as per the treatment setup and slightly covered by soil to avoid a direct contact of the seeds with the fertilizers. Urea and DAP were used as a source of nitrogen and phosphorus respectively. Urea was applied in split as per the treatments while DAP was applied once at planting. Each plot was having an area of 15m2 (3.75 m by 4 m). The space between blocks was 1 m and between plots was 0.5 m. The space between plants and rows was 15 cm and 75 cm; respectively. Misker sorghum variety was used as a test crop. Tie-ridge with 2 meter interval was uniformly applied for all treatments for moisture conservation. Similarly, cultivation and weeding were done uniformly for all treatments.

Data collected

The grain yield was measured after harvesting the above-ground biomass at full physiological maturity from the central rows of the plot excluding the border rows, sun drying, measuring the above-ground biomass (in kg per plot) and then threshing and separating the grains from the straws. The grain yield per plot was reported in kg and was converted to kilograms per hectare. The above-ground biomass yield in kg per plot was also converted to kg per ha.

Data analysis

Collected datas were subjected to statistical analysis using SAS statistical software version 9.0 and significant treatment effects were compared using the Fisher’s Least Significant Differences test at 5% level of significance.

Soil sampling and analysis

A composite soil sample was collected from 0–20 cm before sowing, air-dried and passed through 2 mm sieve to determine pH, ECe and passed through 0.5 mm for total nitrogen and organic carbon. The soil parameters were determined following the standard laboratory procedures. Soil pH was determined in H2O using 1:2.5 soils to solution ratio using a combined glass electrode pH meter11. Soil organic carbon was determined following the wet digestion method as described by12 while percent organic matter of the soils was determined by multiplying the percent organic carbon value by 1.724. Total N was analyzed by the Kjeldahl digestion and distillation procedure13.

Partial budget analysis

The cost benefits and marginal rate of returns of the treatments were analyzed based on the technique described by14. To estimate the economic parameters, the grain of sorghum was valued based on average market price collected from the local markets during the two consecutive production years. The average cost of Urea and DAP fertilizer and labor cost for each fertilizer application were collected from the two districts. The average yield was adjusted downward by 10% from the exact yield to reflect the difference between the experimental yield and yield of farmers. MRR (%) was calculated as changes in net benefit divided by changes in cost.

Ethics approval and consent to participate

It is to declare that we have all the ethical approval and consent from our Research Institute to participate in research paper writing and submission to any relevant journal.

Results and discussion

The soil pH of the surface soil for Aybra-Sekota and Shumshiha-Lasta Lalibela was 6.3 and 6.4 respectively (Table 1). Based on15, the reaction of the study areas is within slightly acidic class. The organic matter content of the soil was 1.0% for Aybra and 1.2% for Shumshiha-Lasta Lalibela. According to16 rating of organic matter it was rated as low. Similarly, the total nitrogen content was 0.01% for Aybra-Sekota and 0.02% for Shumshiha-Lasta Lalibela; which is extremely low according to rating given by15.

Table 1 Selected soil properties for the study areas.
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Effect of nitrogen and phosphorus fertilization on grain and biomass yields

Effects of nitrogen and phosphorus on sorghum grain yield

The maximum grain yield (2476.4 kg ha−1) was obtained from 34.5 kg P2O5 and 30.75 kg N ha−1, (N applied in three splits) while the minimum grain yield (1114.8 kg ha−1) was obtained from the control (without fertilizer) at Aybra-Sekota. Micro-dosing application increased the yield by 122% over the control and by 28.4% over the recommended NP (Table 2) at Aybra-Sekota. Similarly, the maximum grain yield (2476.6 kg ha−1) was obtained from 20.5 kg N ha−1 and 23 kg P2O5 ha−1 (Nitrogen applied in three splits) whereas the minimum yield (1023 kg ha−1) was obtained from the control (without fertilizer) at Shumshiha-Lasta Lalibela (Table 2). In addition to the yield advantages over the recommended NP, micro-dose application saved 25% fertilizer at Aybra and 50% fertilizer amount at Shumshiha-Lasta Laibela. The saved fertilizer amounts can be used for additional sorghum production on 1/3 ha at Aybra-Sekota and on one ha at Shumshiha in a micro-dose application. The result is in line with the findings of 7 and17 who reported that sorghum yield increment ranging between 44 to 120% compared to the control using micro-dose application. Similarly18, reported that application of micro-dose of 10 kg nitrogen ha−1 increased the yield by 30–100%. Three times split application of nitrogen with micro-dosing 1/3 at sowing, 1/3 at emergence and 1/3 at 45 days after emergence was more efficient than the other application methods.

Table 2 Effect of nitrogen and phosphorus fertilization on biomass and grain yield.
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Effects of nitrogen and phosphorus on sorghum biomass yield

At Aybra-Sekota significantly higher biomass yield (6668.2 kg ha−1) was obtained from 34.5 kg P2O5 and 30.75 kg N ha−1, (N applied in three splits) while the minimum biomass yield (4246.3 kg ha−1) was obtained from the control (Table 2). At Shumshiha-Lasta Lalibela the maximum biomass yield (7293 kg ha−1) were obtained from 23 kg P2O5 ad 20.5 kg N ha-1 (Table 2). This implies that micro-dose application increased the biomass yield by 57% over the control and by 21.6% over the recommended NP at Aybra-Sekota and by 85% over the control and 10% over the recommended NP at Shumshiha-Lasta Lalibela. The results are in line with the findings of [7, 17, and 18] who reported increased sorghum biomass due to micro-dose application.

Partial budget analysis

Partial budget analysis of Aybra-Sekota shows that application of 34.5 kg P2O5 and 30.75 kg N ha−1 (N applied in three splits) had the highest net benefit (14051.07 ETB ha−1) with MMR of 518.95% (Table 3). Whereas the partial budget analysis for Shumshiha-Lasta Lalibela shows that application of 20.5 kg N and 23 kg P2O5 ha−1 (N applied in three splits) resulted in the highest net benefit (17844.01 ETB ha−1) (Table 4) with MRR of 14942.3%.

Table 3 Partial budget analysis for Aybra-Sekota.
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Table 4 Partial budget analysis for Shumshiha-Lasta Lalibela.
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Conclusion and recommendation

Micro-dosing fertilizer application was found very important to increase the production and productivity of sorghum. Results from this study confirm that micro-dosing fertilizer application increases sorghum yield than row application. Hence, at Aybra-Sekota, 30.75 kg N ha−1 and 34.5 kg ha−1 P2O5 increased sorghum yield by 28.4% over the recommended rate of 100 kg ha−1 DAP and 50 kg ha−1 urea whereas, 23 P2O5 kg ha−1 and 20.55 kg ha−1 N increased the sorghum yield by 15% over the recommended NP (100 DAP and 50 urea kg ha−1) at Shimshiha-Lasta Lalibela areas. Micro-dosing fertilizer application is simple and cheap with low risk to resource-poor farmers in the dry areas of Wag-Lasta. Therefore, the application of 34.5 kg ha−1 P2O5 and 30.75 kg ha−1 N (N applied in three splits) for Aybra-Sekota and 23 P2O5 kg ha−1 and 20.5 kg ha−1 N (N applied in three splits) for Shumshiha- Lasta Lalibela are recommended for higher sorghum yield and economic utilization of the fertilizers.

Abbreviations

DAP: Di Ammonium Phosphate, ETB: Ethiopian Birr, RCBD: Randomized completed block design, MRR: Marginal Rate of Return, SAS, Statistical Analysis Software, NP: Nitrogen and Phosphorus.