Application of Blended (NPSB) and Urea Fertilizers Levels for Wheat Production across Soil Types and Agro-Ecologies of South- Eastern Ethiopia

Area descriptions

The experiment was carried out on farmers’ fields and research stations for three cropping seasons during 2017- 2019 at Gedeb-Hasasa and Lemu-Bilbilo districts in Arsi zone of Oromia, South-eastern Ethiopia. Geographically, the study area at Gedeb-Hasasa is located between 070 07’ 10.1” to 070 03’ 130” N, and 0390 11’ 54.8” to 0390 07’ 911” E with an elevation ranging from 2372-2407 meters above sea level; and Lemu-Bilbilo is located between 070 36’ 870” to 070 27’ 530” N, and 0390 14’ 270” to 0390 15’ 133” E with an elevation ranging from 2526-2873 meters above sea level.

The average weather data recorded on the weather station located near the study areas from the years 2017 - 2019 indicate that the total annual rainfall for Gedeb-Hasasa district were 496.1, 571.5 and 640.0 mm respectively, and the annual mean minimum and maximum daily air temperature for the consecutive years were (7.3, 6.9, 7.0 0C) and (17.9, 18.1, 21.0 0C) respectively. Similarly, the total annual rainfall for Lemu-Bilbilo district were 956.6, 803.5 and 990.6 mm respectively, and the annual mean minimum and maximum daily air temperature for the consecutive years were (4.7, 2.9, 3.3 0C) and (18.5, 20.3, 20.5 0C) respectively.

Design and Treatments

The experiment was set in combined RCBD by varying levels of NPSB fertilizer (0, 100, 150, 200, 250 kg ha-1), urea (0, 150, 250, 350 kg ha-1) and recommended NP with three replications. The size of each experimental gross plot was 2.6 m * 4 m (10.4 m2). The bread wheat variety used for the experiment at Gedeb-Hasasa and Lemu-Bilbilo were Wane and Lemu, respectively. Both fertilizers which varied depending on treatments were applied as side banding at sowing time, urea was applied two times in split half at planting and the remaining at 35 days after planting, the other agronomic practices were kept uniform for all treatments.

Soil Sampling and Analysis

Surface soil, 0 - 20 cm depth, were collected from the entire experimental field before planting and after harvesting. The soil was daily air dried and made fine by using mortar and pestle. The fined soil was passed through 2mm sieve and the soil pH, Available P, Total N and Organic matter were determined at Kulumsa Agricultural soil Laboratory. Soil pH (H2O) was measured by using a pH meter in a 1:2.5 soil: water ratio. Soil organic carbon was estimated by the Walkley-Black wet oxidation method. Total nitrogen was determined by the micro-Kjeldahl digestion, distillation and titration method, and available P was determined using the standard Olsen extraction method. Accordingly, the soil analysis result taken before planting at Gedeb-Hasasa and Lemu-Bilbilo districts indicated that the pH value were 5.88 and 5.62 (moderate) [12], available phosphorus 14.36 (high) and 9.03 (medium) [13], total N 0.14 (medium) and 0.27 (high), and Organic matter 2.36 and 3.36 %, low [14], respectively (Table 1).

Yield Data Collection

Data of seedling density, tiller per plant, plant height, number of spike per 50cm, spike length, number of seed per spike, grain yield, above ground biomass, and thousand seed grain weight and hectoliter weight were collected from each plot. Grain and above ground biomass yield were analyzed gravimetrically by using sensitive balance and recorded in units of gram.

Statistical Analysis

The ANOVA procedure of statistical analysis system SAS Institute [15] was used for performing the significance of differences in grain and above ground biomass yields. A post hoc separation of means was done by least significant difference (LSD) test after main effects was found significant at P < 0.05.

Effect of Fertilizer Application on Soil Chemical Properties

The soil analysis result at post-harvest at Gedeb- Hasasa district showed that the application of treatments significantly (p < 0.01) affected pH, total N, organic matter, and available P for samples taken from experimental sites of wheat crop. Application of different fertilizer levels had significant effects on post-harvest pH and organic carbon contents. A significant improvement was not observed in soil chemical contents except available P and total N compared to the contents of the soil before treatment application (Table2).

, * = significant at p < 0.01 and p < 0.001 Table 2: Effect of fertilizer levels on soil chemical properties after harvesting wheat in Gedeb-Hasasa district.

Similarly, the soil analysis result after harvest revealed that the application of treatments significantly (p < 0.01) affected total N, organic carbon, and available P for samples taken from experimental sites of wheat crop. Soil pH of wheat field was significantly (p < 0.05) affected by different fertilizer treatments. Different fertilizer treatments had significant effects on post harvest soil organic carbon content. A significant decrement was observed in pH content of soil compared to the contents of the soil before treatment application at Lemu-Bilbilo district (Table 3).

*, , * = significant at p < 0.05, p < 0.01 and p < 0.001 Table 3: Effect of fertilizer levels on soil chemical properties after harvesting wheat in Lemu-Bilbilo district.

Effect of NPSB and Urea Fertilizers on Grain Yield and Yield Components of Wheat

Agronomic maximum grain and above ground biomass yield (6170 and 13510 kg ha-1) in 2017 and minimum (4038 and 10908 kg ha-1) in 2018 cropping season were obtained, respectively at Gedeb-Hasasa district up on the application of NPSB and urea fertilizers. Similarly, significant grain and above ground biomass yield (6440 and 14846 kg ha-1) were obtained from the application of 250 + 350 kg ha-1 NPSB + urea rate, respectively (Table 4).

Agronomic maximum grain and above ground biomass yield (6584 and 12709 kg ha-1) in 2019 and minimum (5229 and 10674 kg ha-1) in 2018 cropping season were obtained, respectively at Lemu-Bilbilo district up on the application of NPSB and urea fertilizers. Similarly, significant grain and above ground biomass yield (6629 and 13372 kg ha-1) were obtained from the application of 250 and 350 kg ha-1 NPSB and urea fertilizers rate (Table 4).

Maximum harvest index, HLW and thousand seed weight (44.8 %, 78.8 ghL-1 and 42.4 g) in 2017 and minimum (39.1 % and 75.6 ghL-1) in 2019, and (38.43 g) in 2018 cropping season were obtained, respectively at Gedeb-Hasasa district up on the application of NPSB and urea fertilizers. Similarly, significant value of harvest index and thousand seed weight (43.1% and 42.2g) were obtained from the application of (200, 150) and (250, 150) kg ha-1 NPSB and urea fertilizers respectively. HLW was not significantly different across the fertilizer rates (Table 5).

The highest value of harvest index (45.1%) in 2018 and 2019, HLW (83.8 ghL-1) in 2017 and thousand seed weight (46.8 g) in 2018 and minimum (41.5%) in 2017, (78.2 ghL-1) in 2019 and (44.6 g) in 2019 cropping season were obtained, respectively at Lemu-Bilbilo district up on the application of NPSB and urea fertilizers. Similarly, significant value of harvest index (44.8%) at the control and thousand seed weight (46.5 g) was obtained from the application of (100, 250) kg ha-1 NPSB and urea fertilizers respectively. The value of HLW was not significantly different across the fertilizer rates (Table 5).