Effects of integrated fertilizer application on selected soil properties and yield attributes of common bean (Phaseolus vulgaris L.) on different soil types.

In Ethiopia, common bean (Phaseolus vulgaris L.) productivity remains low because of low soil fertility. However, both plant production and soil fertility benefit from integrated application of fertilizers. Thus, this study investigates the effect of integrated application of inorganic, organic and biofertilizers on selected soil properties and yield components of common bean. A field experiment was conducted at three sites in southern Ethiopia, under two consecutive cropping season (2021 and 2022). The experiment was conducted using a randomized complete block design (RCBD) with three replications. The treatments included three levels of inorganic fertilizer (Triple Superphosphate, TSP), applied at 0, 42.5, and 85 kg TSP ha⁻1 for Kokate; 0, 29, and 58 kg TSP ha⁻1 for Hawassa; and 0, 35.5, and 71 kg TSP ha⁻1 for Alage, tailored to the specific conditions of each site. Additionally, the experiment incorporated three levels of organic inputs 0, 5 t biochar ha⁻1, and 5 t compost ha⁻1 as well as Rhizobium inoculation (HB-429) applied at 500 g ha⁻1. These treatments were designed to assess the combined effects of inorganic, organic and biofertilizers on soil health and crop performance. Results showed that the integrated application of inorganic, and organic fertilizers significantly (p ≤ 0.05) improved soil pH, soil organic carbon, and available P compared with the sole fertilizer application plots. Similarly, the integrated use of inorganic, organic and biofertilizers increased nodule numbers, seed weight, grain yield, and biomass yield. We also found that 23 and 24 % higher grain yield were achieved with integrated applications of TSP fertilizer with compost on Hawassa and Alage sites than sole inorganic fertilizer application. On the other hand, the integrated application of TSP fertilizer with biochar increased by 18 % grain yield on Kokate over the sole application of inorganic fertilizer. The highest economic benefit of 69,460 and 63,250 ETB was obtained from the integrated application of TSP fertilizer with compost at Hawassa and Alage sites, respectively. The highest economic benefit for the Kokate site was 53,583 ETB at TSP fertilizer with biochar application. Overall, the study confirms that site-specific integrated soil fertility management appears to be a prerequisite for sustainable and profitable common bean production over sole fertilizer application in southern Ethiopia.

Optimizing fertilization schemes to narrow the maize yield gap in smallholder farming systems in southern Ethiopia.

Maize (Zea mays L.) is an important food crop in Ethiopia, but productivity is low mainly due to low soil fertility and suboptimal fertilization. Therefore, this study aims to determine the yield, nutrient use efficiency and economic feasibility of maize production under various fertilizer applications and test the suitability of the Quantitative Evaluation of the Fertility in Tropical Soils (QUEFTS) model for predicting maize yield response to fertilization in Sidama region, southern Ethiopia. On-farm experiments were conducted at six sites (Site 1-6) of Sidama region, southern Ethiopia during the 2019 growing season. The experiments were laid out in a randomized complete block design (RCBD) with three replications. The experiment was a nutrient omission trial with seven treatments: control, two full NPK treatments and four nutrient omission treatments with contrasting N and P rates. Omitting N resulted in 5-28 % yield loss and omitting P resulted in 4-44 % yield loss compared to the lower rate of full NPK treatment across all study sites. Whereas omitting K resulted in 21 % yield loss only at sites 2 and 3. An increase in maize yield was mainly associated with an increase in both nutrient uptake and nutrient use efficiency of NPK. The results showed the need to revise blanket recommendations since the highest mean grain yields and net economic returns with acceptable marginal rates of return were obtained with NPK application or higher levels of NP (N2P2 treatment). In addition, the present QUEFTS model validation study revealed the good fit between QUEFTS model predicted maize grain yields (6.3 t ha-1) to the average actual yields (7.4 t ha-1) and this was also confirmed by small average values of RMSE = 1.5 t ha-1 and PBIAS = 6.9 %. Thus, the model can be a promising option for development of site specific fertilizer recommendations under smallholder farming systems in the region.