SOIL FERTILITY STATUS AND RESPONSE OF HIGHLAND MAIZE (Zea mays L.) TO THE APPLICATION OF MINERAL AND ORGANIC FERTILIZERS IN AMBO AND TOKE-KUTAYE DISTRICTS, CENTRAL ETHIOPIA

Abstract

Maize is one of the most important food security crops widely cultivated for multiple nutritional benefits in sub-Saharan Africa including Ethiopia. Low soil fertility and insufficient use of fertilizers as well as inappropriate rate and timing of nitrogen application are among the major causes of low maize yield in Ethiopia. Under such conditions, identifying the nutrient status of the soil and improving the soil fertility could be an important avenue to enhance yields of highland maize in the country. However, to date, little or no research has been done to explicate the productivity and nutrient efficiency of highland maize in the area using different types and rates of fertilizers. Therefore, research was conducted in Ambo and Toke-Kutaye districts with the objective of assessing soil fertility status and determining the response of the crop to the application of fertilizers in these areas. In addition to the survey study, three field experiments were conducted. The experiments were laid out as randomized complete block design in a factorial arrangement and replicated three times per treatment. An improved highland maize hybrid variety AMH-851- ‘Jibat’ was used as a test crop. Data were collected on phenology, growth, yield components and yield of the crop. Prior to conducting the field experiments in Ambo and Toke-Kutaye districts, 110 surface (0–30 cm depth) and the sub-surface (30–60 cm depth) soil samples were collected randomly from both districts and analyzed for the major soil physical and chemical properties. The results revealed that in both districts, the texture of the soil is clayey; the bulk density of the surface soil ranges between 1.1 g cm–3 to 1.6 g cm–3 whereas that of the sub-surface soil ranges between 1.3 g cm–3 to 1.7 g cm–3. The pH values of the soils in Ambo district ranges between moderate acidity (5.42) to moderate alkalinity (7.61), whereas that of Toke-Kutaye district ranges between strongly (4.87) to slightly acidity (6.4). The available soil phosphorus, sulphur, boron, zinc, organic carbon, and total nitrogen contents of both districts were predominantly low. The availability of exchangeable potassium in soils of Ambo district is medium (0.37 cmol (+) kg–1) whereas that of Toke-Kutaye district is low (0.22 cmol (+) kg–1). The findings imply that to increase crop yield and enhance farmers’ livelihoods in the study area, adequate recommendations of xxi fertilizers containing the deficient nutrients, and organic carbon need to be formulated to enhance and sustain crop production. Based on the survey results the subsequent field experiment was conducted to determine the effects of different rates of nitrogen and phosphorus fertilizers on growth, yield components and yield of highland maize in Ambo and Toke-Kutaye districts during the 2019 and 2020 main cropping seasons. The treatments consisted of four rates of nitrogen (0, 46, 92, and 138 kg N ha–1) and five rates of phosphorus (0, 23, 46, 69, and 92 kg P2O5 ha–1). The results of the study showed that the combination of 92 kg N ha–1+ 69 kg P2O5 ha–1application resulted in the highest maize grain yields of 9659.57 kg ha–1 and 9252.94 kg ha–1 in Ambo and Toke-Kutaye districts, respectively. This was at statistical parity and followed by the interaction effect of applying 138 kg N ha–1 + 69 kg P2O5 ha–1, which significantly (p ≤ 0.05) increased the growth, yield components and yield of maize compared to the other treatments. It is concluded that applying 92 kg N ha–1 + 69 kg P2O5 ha–1 significantly enhanced grain yield, which was agronomically feasible and economically profitable in both districts. The third experiment was conducted to determine the effect of applying vermicompost and inorganic fertilizers on growth, yield components, and yield of highland maize. The treatments consisted of two rates of combined mineral NP fertilizer (0/0, 46/46 N/P2O5 ha–1), three rates of vermicompost (VC) (0, 4, and 8 t ha–1), and three rates of blanket recommended blended fertilizer (0, 50, and 100% recommended NPSB ha–1). The results revealed that the yield and yield components of maize significantly (p ≤ 0.01) increased in response to the application of the fertilizers. For Ambo district, combined application of 8 t ha–1 VC with 50% RD of the NPSB in conjunction with 46/46 N/P2O5 kg ha–1 increased grain yield (10295.53 kg ha–1) of the crop by 317% over the control treatment (2468.9 kg ha–1). Similarly, in Toke-Kutaye district combined application of 4 t ha–1 VC in conjunction with applying mineral fertilizer at 46/46 N/P2O5 kg ha–1+ 50% RD of the NPSB increased grain yield (9315.82 kg ha–1) significantly by 319% over the control treatment (2221.59 kg ha–1). Partial budget analysis showed that the highest net benefits of 133, 499.70 ETB ha–1 with acceptable marginal rates of return in response to applying 8 t VC ha–1in combination with 46/46 kg N/P2O5 ha–1+ 50% RD of NPSB in Ambo district. Likewise, in the Toke-Kutaye district, net benefit of 121023.57 ETB ha–1with acceptable marginal rates of return was obtained in response to applying 4 t VC ha–1in combination with 46/46 kg N/P2O5 ha–1+ 50% RD of NPSB ha–1. The results also showed that applying vermicompost increased xxii the contents of organic carbon, total N, available P, and pH of the soil in the study area. In conclusion, applying integrated mineral and organic fertilizers increased crop yields, generated higher income than sole N, P, or VC fertilizer and improved soil fertility as well as soil pH to enhance crop productivity in the districts on a sustainable basis. The fourth field experiment was conducted in the research field of Ambo Agricultural Research Center to determine the effect of rate and timing of N application on yield, yield components, and N use efficiency of highland maize. The treatments consisted of three rates of N (0, 46, and 92 kg ha– 1) and seven timing of applying the fertilizer to the crop (full dose at planting and full dose at knee-height of growth; ½ at planting and ½ at knee-height; ⅓rd at planting + ⅓rd at knee- height + ⅓rd at tasseling; ⅓rd at planting and ⅔rd at knee-height; ¼th at planting + ½ at knee- height + ¼th at tasseling; ¼th at planting and ¾th at knee-height). The results revealed that the grain yield of the crop and its yield components increased significantly in response to increasing the rate and the number of times of applying the fertilizer. Applying 46 kg N ha–1 and 92 kg N ha–1 in three split doses of ¼th at planting + ½ at knee-height + ¼th at tasseling resulted in the highest grain yield, yield components, protein content, N uptake and N use efficiency compared to applying the fertilizer rates only once at full dose and the farmers’ practice of twice split application of ½ at planting + ½ at knee-height. The highest grain yield (9891 kg ha–1), N use efficiency (53.7%), grain protein content (9.7%), and net income return (130411.65 ETB ha–1) were obtained in response to the application of 92 kg N ha–1 in three split doses. The results imply that farmers in the study area should integrate application of mineral and organic fertilizers as well as apply nitrogen fertilizer (92 kg N ha–1) in three split doses of ¼th at planting, ½ at knee-height stage of growth, and ¼th at tasseling to increase productivity of the crop and its grain quality on a sustainable basis